January 2006, Volume 48 Issue 1, Pages 1-120.


Cover Caption:
Cortical microtubules are known to play important roles in cell morphogenesis, but it is not clear whether they are essential for normal cell wall synthesis. In this issue, Burk et al. show that disruption of normal cortical microtubules by expression of an excess amount of green fluorescent protein-tagged a-tubulin 6 in transgenic Arabidopsis plants causes a dramatic reduction in overall cell wall synthesis. This finding demonstrates that the transverse orientation of cortical microtubules along the elongation axis is essential for both cell morphogenesis and normal synthesis of plant cell walls. The cover images show flowers with severely reduced length of stamen filaments from transgenic plants with altered cortical microtubule organization (bottom right) compared with the wild type (top left). See pages 85-98 for more details.

 

          Research Articles
Recent Progress in Arabidopsis Research in China: A Preface  
Author: Zhi-Hong Xu
Journal of Integrative Plant Biology 2006 48(1): 1-4
      
    In 2002, a workshop on Arabidopsis research in China was held in Shanghai, when a small group of Chinese plant scientists was working on this model species. Since then, we have witnessed the rapid growth of Arabidopsis research in China. This special issue of Journal of Integrative Plant Biology is dedicated exclusively to the Fourth Workshop on Arabidopsis Research in China, scheduled on November 30, 2005, in Beijing. In addition to reports collected in this special issue, the Chinese Arabidopsis community has been able to make significant contributions to many research fields. Here, I briefly summarize recent advances in Arabidopsis research in China. Fatty acid homeostasis has long been thought as an important mechanism to regulate cellular signaling in a variety of organisms, but little is known about the direct physiological consequence of this regulation in higher plants. The characterization of the MOD1 gene demonstrated that de novo fatty acid synthesis is fundamental for plant growth and development by regulating various cellular signaling activities, such as apoptosis. The MOD1 gene encodes an enoyl-acyl carrier protein reductase, which is a subunit of the fatty acid synthase complex. The mod1 mutation causes premature cell death and a variety of developmental defects (Mou et al. 2000). Analogously, a loss-of-function mutation in the PEAMT gene, which encodes a rate-limiting enzyme involved in an early step of membrane phospholipid phosphatidylcholine biosynthesis, causes a pleiotropic phenotype and temperature-sensitive male sterility, as well as hypersensitivity to salinity, highlighting the importance of this class of complex lipids in plant cellular signaling (Mou et al. 2002). In efforts to elucidate the molecular mechanism of leaf development, ERECTA was defined to act in the ASYMMETRIC LEAVES1 (AS1)-AS2 pathway, in which AS1 and AS2 may form a complex (Xu et al. 2003). Surprisingly, AS1and AS2 act synergistically with the RNA-dependent RNA polymerase RDR6 to repress BREVIPEDICELLUS (BP) and MicroRNA165/166 (miRNA165/166), which likely target class III HD-ZIP proteins (Li et al. 2005). Therefore, this highly interactive network plays a key role in specifying leaf adaxial identity. A systematic characterization of BP function is also reported in this issue (Wang et al. 2006). The WUSCHEL (WUS) gene is well known as a key component of shoot meristem development. A gain-of-function mutation in WUS causes the formation of ectopic floral buds along inflorescence stems, thus revealing a novel function of the homeodomain protein in floral meristem development (Xu et al. 2005). During reproductive development, the SLOW WALKER1 (SWA1) gene, encoding a WD40 protein involved in rRNA biogenesis, was found to be essential for the cell cycle progression during gametogenesis. The swa1 mutation causes asynchronous development of megagametophytes, leading to the developmental arrest of embryo sacs at various stages. In addition, SWA1 also appears to play a role in root development (Shi et al. 2005). Genome-wide identification and characterization of Arabidopsis S-locus F-box-like (AtSFL) genes have shed light on the molecular functions of these Antirrhinum orthologs in plant growth and development. It is interesting to note that mutations in several AtSFL genes cause defective embryogenesis or female gametogenesis (Wang et al. 2004). De novo synthesis of the phytohormone auxin has been thought to be primarily through a tryptophan (Trp)-dependent pathway. However, a Trp-independent pathway was identified and characterized, in which indole-3-glycerol phosphate appears to act as a branch-point compound in this novel pathway (Ouyang et al. 2000). More recently, an indole-3-acetic acid (IAA) carboxyl methyltransferase (IAMT1) was shown to convert IAA into methyl-IAA ester, thereby regulating auxin homeostasis. A gain-of-function mutation in IAMT1 causes dramatic hyponastic leaf phenotypes, consistent with a decreased expression level of several TCP genes that are known to regulate leaf curvature (Qin et al. 2005). In auxin signaling, the BUD1/MAPKK7 gene was characterized as a negative regulator of polar auxin transport and the gain-of-function mutant bud1 displays pleiotropic phenotype characteristics of the auxin-deficient syndrome (Dai et al. 2006). This study provides the first line of evidence showing the involvement of the conserved mitogen-activated protein kinase signaling cascade in the control of auxin signal transduction. In parallel with these findings, Auxin Response Factor (ARF) 10 and ARF16, two key regulators controlling root cap development, were found to be targeted by miRNA160. Overexpression of miRNA160 displays a phenotype similar to that of an arf10/arf16 double mutant, characteristics of uncontrolled cell divisions and blocked cell differentiation in the root distal region, thereby causing the formation of a tumor-like root apex and the loss of gravity sensing. Interestingly, the repression of ARF10 and ARF16 by miRNA160 appears to be auxin independent (Wang et al. 2005). Previous genetic and molecular studies indicate that auxin-mediated lateral root development requires multiple components, such as the transcription factor NAC1 and an F-box protein TIR1. However, two recent studies suggest that the regulatory network is more complicated than expected. Overexpression of the novel transcription factor gene NAC2 promotes the formation of lateral roots, a phenotype similar to that of NAC1. In contrast with NAC1, NAC2 is regulated by auxin, ethylene, and abscisic acid (ABA), as well as by salt stress. Moreover, the salt regulation of NAC2 requires functional auxin and ethylene pathways, although its physiological significance remains unclear. It was proposed that NAC2 functions in regulating lateral root development by the integration of environmental and endogenous stimuli (He et al. 2005). A second new player in lateral root development is the auxin-inducible gene CEGENDUO (CEG), which encodes a novel F-box protein. The formation of lateral roots is promoted in a ceg-knockout mutant, but inhibited in transgenic plants overexpressing CEG. Therefore, CEG appears to negatively regulate lateral root formation in an auxin-dependent manner (Dong et al. 2006). Although polar transport of auxin has been well documented, very little is known about the transport of other plant hormones. Equilibrative nucleoside transporters (ENTs) are a class of evolutionarily conserved proteins that are involved in the transport of nucleosides in all eukaryotic organisms. Molecular and biochemical studies identified eight ENT genes in the Arabidopsis genome (Li et al. 2003). A recent study suggests that AtENT8/SOI33 and AtENT3 appear to function as transporters of cytokinin, a phytohormone derived from nucleosides (Sun et al. 2005). Equally exciting findings were also made in studies on brassinosteroid signaling. Brassinosteroids have long been appreciated as key regulators of cell elongation. However, brassinosteroids were also found to be important for cell division in a CycD3-dependent manner (Hu et al. 2000). Moreover, brassinosteroids were found not only to alter the expression of PIN genes, which encode auxin efflux carrier proteins, but also to promote functional localization of PIN2 modulated by ROP. Consistent with these observations, brassinosteroids were manifested to promote plant tropisms by modulating polar auxin transport (Li et al. 2005). Remarkably, a novel membrane steroid-binding protein (MSBP1) was found to be capable of binding various steroids, including 24-epi-brassinolide, in an in vitro assay. Transgenic studies suggest that the MSBP1 expression level is well correlated with the steroid-binding capacity, reduced cell elongation, and shorter hypocotyls, as well as sensitivities to exogenous progesterone and 24-epi-brassinolide. Thus, the light-responsive MSBP1 acts as a negative regulator of steroid signaling by controlling cell elongation and hypocotyl elongation (Yang et al. 2005). This study identifies the first functional steroid-binding protein in higher plants. Cryptochrome1 (CRY1) is a blue light receptor that mediates light signaling, presumably through its C-terminal domain. In an effort to characterize the N-terminal domain of CRY1 functionally, Sang et al. (2005) revealed that this domain was essential for dimerization of the photoreceptor, which, in turn, was required for light activation of the C-terminal domain. Intriguingly, CRY1 and CRY2 were also shown to be involved in the control of stomatal opening, which is physiologically connected to both water evaporation and photosynthesis in plants (Mao et al. 2005). Calcium has been implied in many aspects of cellular signaling in plants. The PPF1 gene, encoding a putative calcium ion carrier, is functional in both plant and human cells. The PPF1 gene appears to play an important role in multiple signaling pathways, particularly in the control of the flowering time. Indeed, whereas overexpression of PPF1 caused a late flowering phenotype, suppression of PPF1 expression resulted in an opposite phenotype (Wang et al. 2003). On the other hand, biochemical and physiological studies have demonstrated the presence of the Ca2+-permeable channels in the plasma membranes of pollens and pollen tubes. Moreover, dynamic actin microfilaments have been shown to control Ca2+ channel activity, which may, consequently, regulate cytoplasmic Ca2+, thus playing crucial roles in the regulation of pollen germination and tube growth (Wang et al. 2004). Cytosolic free Ca2+ in the regulation of stomatal movement has also been documented. Extracellular calmodulin was found to induce an increased level of H2O2 and cytosolic free Ca2+, leading to a reduction in stomatal aperture. Genetic analysis indicates that the extracellular calmodulin-modulated intracellular signaling is involved in the activation of a heterotrimeric G-protein (Chen et al. 2004). Epigenetic control of plant growth and development has been emerging as a main theme in recent years. In addition to the functional characterization of several microRNAs highlighted above, two recent studies have provided important insights into the epigenetic regulation in Arabidopsis. In root development, the identity of epidermal cells is determined by a small group patterning genes. Hyperacetylation of the core histones H3 and H4, manipulated by trichostatin A (TSA; an inhibitor of histone deacetylase) treatment or a mutation in a histone deacetylase gene, altered the expression of these patterning genes, thereby causing misspecified identity of certain epidermal cells (Xu et al. 2005). In a genetic screen for suppressors of ros1, which causes transcriptional silencing of a transgene and a homologous endogenous gene (Gong et al. 2002), two allelic mutants, namely ror1-1 and ror1-2, were identified. The ROR1 gene, encoding a protein similar to DNA replication protein A2, is involved in epigenetic gene silencing, likely in a DNA methylation-independent manner (Xia et al. 2006). In efforts in functional genomics programs, an ORFeome collection, representing 1 282 Arabidopsis transcription factor (TF) genes, was generated. Using a 70-mer-oligo array, the expression profiles of 66 MADS-box transcription factor genes and the relative distribution of expression abundance of 858 transcription factors were analyzed (Gong et al. 2004). A database of Arabidopsis transcription factors (DATF), representing 1 826 TF genes from 56 families, has been established at Peking University (Guo et al. 2005; see also http://datf.cbi.pku.edu.cn). Among these TF genes, two families, AP2/EREBP (Feng et al. 2005) and MYB (Chen et al. 2005), have been analyzed systematically and intensively. In addition, more than 125 000 T-DNA activation tagging lines were generated. These lines were generated using a 35S enhancer vector (PKU lines; 85 000 lines) and a chemical-inducible vector (IGDB lines; 40 000 lines), of which approximate 30 000 lines have been released to academic users (Qin et al. 2003; Zhang et al. 2005). Whereas these tremendous efforts and impressive achievements have been made during the past few years at a remarkably encouraging pace, the Arabidopsis research community keeps growing and becoming stronger in China. Therefore, we have every reason to believe in a great future for this young and energetic community. Acknowledgements I am grateful to Drs Jia-Yang Li, Yong-Biao Xue, Kang Chong, Hong-Wei Xue, Wei-Cai Yang and Jian-Ru Zuo for critically reading the manuscript. I would apologize to colleagues whose work is not cited in this minireview owing to space limitations.(Author for correspondence.College of Life Sciences, Peking University, Beijing 100871, China.Tel: +86 (0)10 6275 1200; Fax: +86 (0)10 6275 1207; E-mail: xuzh@pku.edu.cn)
Abstract (Browse 4550)       
Gene Discovery and Functional Analyses in the Model Plant Arabidopsis  
Author: Cai-Ping Feng and John Mundy
Journal of Integrative Plant Biology 2006 48(1): 5-14
      
    The present mini-review describes newer methods and strategies, including transposon and T-DNA insertions, TILLING, Deleteagene, and RNA interference, to functionally analyze genes of interest in the model plant Arabidopsis. The relative advantages and disadvantages of the systems are also discussed.(Author for correspondence.Tel: +45 3532 2130; Fax: +45 3532 2128; E-mail: mundy@my.molbio.ku.dk)
Abstract (Browse 3360)       
Requirement of KNAT1/BP for the Development of Abscission Zones in Arabidopsis thaliana  
Author: Xiao-Qun Wang, Wei-Hui XU, Li-Geng Ma, Zhi-Ming Fu, Xing-Wang Deng, Jia-Yang Li and Yong-Hong Wang
Journal of Integrative Plant Biology 2006 48(1): 15-26
DOI: 10.1111/j.1744-7909.2006.00181.x
      
    The KNAT1 gene is a member of the Class I KNOX homeobox gene family and is thought to play an important role in meristem development and leaf morphogenesis. Recent studies have demonstrated that KNAT1/BP regulates the architecture of the inflorescence by affecting pedicle development in Arabidopsis thaliana. Herein, we report the characterization of an Arabidopsis T-DNA insertion mutant that shares considerable phenotypic similarity to the previously identified mutant brevipedicle (bp). Molecular and genetic analyses showed that the mutant is allelic to bp and that the T-DNA is located within the first helix of the KNAT1 homeodomain (HD). Although the mutation causes a typical abnormality of short pedicles, propendent siliques, and semidwarfism, no obvious defects are observed in the vegetative stage. A study on cell morphology showed that asymmetrical division and inhibition of cell elongation contribute to the downward-pointing and shorter pedicle phenotype. Loss of KNAT/BP function results in the abnormal development of abscission zones. Microarray analysis of gene expression profiling suggests that KNAT1/BP may regulate abscission zone development through hormone signaling and hormone metabolism in Arabidopsis.(Author for correspondence.State Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China. Tel: +86 10 6488 9377; Fax: +86 10 6487 3428; E-mail: yhwang@genetics.ac.cn)
Abstract (Browse 3589)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
DELAYED FLOWERING, an Arabidopsis Gene That Acts in the Autonomous Flowering Promotion Pathway and Is Required for Normal Development  
Author: Ming-Jie Chen, Zheng Yuan and Hai Huang
Journal of Integrative Plant Biology 2006 48(1): 27-34
DOI: 10.1111/j.1744-7909.2006.00185.x
      
    The control of flowering time in higher plants is one of the most important physiological processes and is critical for their reproductive success. To investigate the mechanisms controlling flowering time, we screened for Arabidopsis mutants with late-flowering phenotypes. One mutant, designated delayed flowering (dfr) in the Landsberg erecta (Ler) ecotype, was identified with delayed flowering time. Genetic analysis revealed that dfr is a single gene recessive nuclear mutant and the mutation was mapped to a locus tightly linked to UFO on chromosome 1. To our knowledge, no gene regulating flowering time has been reported yet in this region. The dfr mutant plant showed a delayed flowering time under the different growth conditions examined, including long- and short-day photoperiods and gibberellic acid GA3 treatments, suggesting that DFR is a gene involved in the autonomous flowering promotion pathway. The Arabidopsis gene FLOWERING LOCUS C (FLC) plays a central role in repressing flowering and its transcripts are undetectable in wild-type Ler. However, FLC expression was upregulated in the dfr mutant, suggesting that DFR is a negative regulator of FLC. In addition, the dfr mutant plant displayed altered valve shapes of the silique and the number of trichomes and branches of each trichome were both reduced, indicating that the DRF gene is also required for normal plant development. Moreover, dfr leafy-5 (lfy-5) double mutant plants showed a much later flowering time than either dfr or lfy-5 single mutants, indicating that DFR and LFY act synergistically to promote flowering in Arabidopsis.(Author for correspondence.Tel: 021 5492 4088; Fax: 021 5492 4015; E-mail:hhuang@sippe.ac.cn)
Abstract (Browse 3678)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Ectopic Expression of a Phytase Gene from Medicago truncatula Barrel Medic Enhances Phosphorus Absorption in Plants  
Author: Kai Xiao, Jian-Heng Zhang, Maria Harrison and Zeng-Yu Wang
Journal of Integrative Plant Biology 2006 48(1)
DOI: 10.1111/j.1744-7909.2006.00189.x
      
    Retraction Statement I recently submitted two papers to the Journal of Integrative Plant Biology and they have been published in 2006, Vol. 48 (1), 35每43 (K. Xiao, J.-H Zhang, M. Harrison and Z.-Y Wang. Ectopic Expression of a Phytase Gene from Medicago truncatula Barrel Medic Enhances Phosphorus Absorption in Plants) and 2006, Vol. 48 (2), 204每211 (K. Xiao, M. Harrison and Z.-Y Wang. Cloning and haracterization of a Novel Purple Acid Phosphatase Gene (MtPAP1) from Medicago truncatula Barrel Medic). These two papers in the Journal of Integrative Plant Biology contain data that were in two papers that had been submitted earlier to the journals Planta (K. Xiao, M. Harrison and Z.-Y Wang. 2005. Transgenic expression of a novel M. truncatula phytase gene results in improved acquisition of organic phosphorus by Arabidopsis, Vol. 222, 27每36) and Plant Science (K. Xiao, H. Katagi, M. Harrison and Z.-Y. Wang. 2006. Improved phosphorus acquisition and biomass production in Arabidopsis by transgenic expression of a purple acid phosphatase gene from M. truncatula by 170:191每202). I am very sorry that the papers with some duplicate data, which was firstly used in the papers published in Planta and Plant Science, were re-published in the Journal of Integrative Plant Biology. When I submitted the manuscripts to the Journal of Integrative Plant Biology, the co-authors M. Harrison and Z.-Y. Wang were not involved and therefore were not aware of the submissions until after these papers were published. Therefore, it is my fault to cause these adverse results. Here I am regretful to have made some damage to their reputations. As the corresponding author for the Journal of Integrative Plant Biology papers, here I retract the papers published in the Journal of Integrative Plant Biology (2006, Vol. 48 (1), 35每43 and 2006, Vol. 48 (2), 204每211). I apologize for any adverse consequences and inconveniences that may have resulted from the publications of these papers. Sincerely Kai Xiao College of Agronomy Hebei Agricultural University
Abstract (Browse 3836)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Physiological and Molecular Features of the Pathosystem Arabidopsis thaliana L.-Sclerotinia sclerotiorum Libert  
Author: Fu-Ming Dai, Tong Xu, Gerhard A Wolf and Zu-Hua He
Journal of Integrative Plant Biology 2006 48(1): 44-52
DOI: 10.1111/j.1744-7909.2006.00204.x
      
    The fungal pathogen Sclerotinia sclerotiorum Libert causes rot diseases on many crops worldwide and large economic losses occur frequently because of a lack of resistant varieties. The pathogenesis of S. sclerotiorum and the molecular basis of plant responses to the pathogen are poorly understood. In the present investigation, the process of S. sclerotiorum infection in Arabidopsis thaliana L., a plant that is highly susceptible to this fungus, was analysed. In addition, the defense activation in the host was investigated. A convenient inoculation method using millet grain was developed for S. sclerotiorum in Arabidopsis. The fungus rapidly infected the plants, probably through ball- or cushion-like infection structures. Visible symptoms developed within 24 h and plants were killed 72 h after inoculation. Cellulase, the main enzyme that caused host tissues to rot, was secreted by S. sclerotiorum in a pH-dependent manner. Oxalic acid, another pathogenic factor secreted by the fungus, induced necrotic lesions on the leaves. Infection with S. sclerotiorum strongly induced the production of the pathogenesis-related (PR) proteins 汕-1,3-glucanase and chitinase in Arabidopsis. Furthermore, the PR gene PDF.1 was induced, but not PR1, indicating that the pathogen activated basal defense of jasmonic acid/ethylene dependence, which is consistent with its necrotrophic characteristics. This pathosystem for Arabidopsis-S. sclerotiorum could provide an approach for the analysis of the interactions between S. sclerotiorum and other crops, thereby facilitating genetic manipulation techniques for controlling this pathogen.(Author for correspondence.Tel: 021 5492 4121; Fax: 021 5492 4015; E-mail: zhhe@sibs.ac.cn)
Abstract (Browse 3320)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Actomyosin is Involved in the Organization of the Microtubule Preprophase Band in Arabidopsis Suspension Cultured Cells  
Author: Chun-Li Li, Zhi-Ling Chen and Ming Yuan
Journal of Integrative Plant Biology 2006 48(1): 53-61
DOI: 10.1111/j.1744-7909.2006.00214.x
      
    The microtubule preprophase bands (PPBs) participate in the sequence of events to position cell plates in most plants. However, the mechanism of PPB formation remains to be clarified. In the present study, the organization of PPBs in Arabidopsis suspension cultured cells was investigated by confocal laser scanning microscopy combined with pharmacological treatments of reagents specific for the cytoskeleton elements. Double staining of F-actin and microtubules (MTs) showed that actin filaments were arranged randomly and no colocalization with cortical MTs was observed in the interphase cells. However, cortical actin filaments showed colocalization with MTs during the formation of PPBs. A broad actin band formed with the broad MT band in the initiation of PPB and narrowed down together with the MT band to form the PPB. Nevertheless, broad MT bands were formed but failed to narrow down in cells treated with the F-actin disruptor latrunculin A. In contrast, in the presence of the F-actin stabilizer phalloidin, PPB formation did not exhibit any abnormality. Therefore, the integrity, but not the dynamics, of the actin cytoskeleton is necessary for the formation of normal PPBs. Treatment with 2, 3-butanedine monoxime, a myosin inhibitor, also resulted in the formation of broad MT bands, indicating that actomyosin may be involved in the rearrangement of MTs to form the PPBs. Double staining of MTs and myosin revealed that myosin concentrated on the PPB region during PPB formation. It is suggested that the actin cytoskeleton at the PPB site may serve as a rack to transport cortical MTs by using myosin when the broad MT band narrows down to form the PPB.(Author for correspondence.Tel: 010 6273 3436; Fax: 010 6273 3491; E-mail: mingyuan@cau.edu.cn)
Abstract (Browse 3036)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Analysis of Global Expression Profiles of Arabidopsis Genes Under Abscisic Acid and H2O2 Applications  
Author: Peng-Cheng Wang, Yan-Yan Du, Guo-Yong An, Yun Zhou, Chen Miao and Chun-Peng Song
Journal of Integrative Plant Biology 2006 48(1): 62-74
DOI: 10.1111/j.1744-7909.2006.00213.x
      
    To gain insight into the coordination of gene expression profiles under abscisic acid (ABA) and H2O2 applications, global changes in gene expression in response to ABA and H2O2 in Arabidopsis seedlings were investigated using GeneChip (Santa Clara, CA, USA) arrays. Among over 24 000 genes present in the arrays, 459 transcripts were found to be significantly increased, whereas another 221 decreased following H2O2 treatment compared with control. Similar to treatment with H2O2, ABA treatment elevated the transcription of 391 genes and repressed that of 322 genes. One hundred and forty-three upregulated genes and 75 downregulated genes were shared between the two treatments and these genes were mainly involved in metabolism, signal transduction, transcription, defense, and resistance. Only two genes, which encode an APETALA2/dehydration-responsive element binding protein (AP2/DREBP) family transcriptional factor and a late embryogenesis-abundant protein, were downregulated by H2O2, but upregulated by ABA. These results suggest that, similar to ABA, H2O2 plays a global role in gene transcription of Arabidopsis seedlings. The transcriptional responses induced by the application of exogenous ABA and H2O2 overlapped substantially. These two treatments regulated most of the downstream genes in a coordinated manner.(Author for correspondence.Tel: 0378 285 5010; Fax: 0378 285 3079; E-mail: songcp@henu.edu.cn)
Abstract (Browse 4085)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Further Analysis of the Function of AtBHLH29 in Regu- lating the Iron Uptake Process in Arabidopsis thaliana  
Author: Juan Zhang, Hui-Fen Zhu, Hui Liang, Kun-Fan Liu, Ai-Min Zhang, Hong-Qing Ling and Dao-Wen Wang
Journal of Integrative Plant Biology 2006 48(1): 75-84
DOI: 10.1111/j.1744-7909.2006.00210.x
      
    Using T-DNA insertion and chemical mutants, two recent studies have shown that AtBHLH29, encoding a putative basic helix-loop-helix (BHLH) protein, is involved in regulating the iron uptake process in Arabidopsis thaliana. Herein, we report that RNA interference (RNAi) mutants can be used to reveal more accurately the genetic function of AtBHLH29. We compared the iron deficiency responses of seven RNAi strains that contained decreasing amounts of AtBHLH29 transcripts. Under high iron conditions (50 米mol/L iron), only in the most severe RNAi strains (R101, R111, and R119) was plant growth significantly retarded. However, these mutants could still survive and produce seeds. This suggests that the function of AtBHLH29 is beneficial, but not absolutely essential, to plant growth when iron supply is not limiting. Under low iron conditions (less than 10 米mol/L iron), the R111 and R119 strains died prematurely, demonstrating that AtBHLH29 is absolutely necessary for plant survival when iron supply is restricted. The transcription of AtBHLH29 was essential for the expression of AtFRO2 (encoding the ferric chelate reductase). In contrast, the expression of AtIRT1 (encoding the high-affinity iron transporter) was not so strongly dependent upon the transcription of AtBHLH29. By transient expression, we found that the AtBHLH29-GUS fusion protein was targeted specifically to the nucleus in plant cells. Interestingly, the nuclear localization of AtBHLH29-GUS was abolished when the four consecutive arginine residues located in the basic region of the putative AtBHLH29 protein were replaced by alanine residues by mutagenesis. The implications of our findings on further studies of the mechanism underlying the function of AtBHLH29 are discussed.(Author for correspondence.Tel (Fax): 010 6485 4467; E-mails: hqling@genetics.ac.cn; dwwang@genetics.ac.cn)
Abstract (Browse 3560)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Disruption of Cortical Microtubules by Overexpression of Green Fluorescent Protein-Tagged 汐-Tubulin 6 Causes a Marked Reduction in Cell Wall Synthesis  
Author: David H. Burk, Ruiqin Zhong, W. Herbert Morrison III and Zheng-Hua Ye
Journal of Integrative Plant Biology 2006 48(1): 85-98
DOI: 10.1111/j.1744-7909.2006.00202.x
      
    It has been known that the transverse orientation of cortical microtubules (MTs) along the elongation axis is essential for normal cell morphogenesis, but whether cortical MTs are essential for normal cell wall synthesis is still not clear. In the present study, we have investigated whether cortical MTs affect cell wall synthesis by direct alteration of the cortical MT organization in Arabidopsis thaliana. Disruption of the cortical MT organization by expression of an excess amount of green fluorescent protein-tagged 汐-tubulin 6 (GFP-TUA6) in transgenic Arabidopsis plants was found to cause a marked reduction in cell wall thickness and a decrease in the cell wall sugars glucose and xylose. Concomitantly, the stem strength of the GFP-TUA6 overexpressors was markedly reduced compared with the wild type. In addition, expression of excess GFP-TUA6 results in an alteration in cell morphogenesis and a severe effect on plant growth and development. Together, these results suggest that the proper organization of cortical MTs is essential for the normal synthesis of plant cell walls.(Author for correspondence.Department of Plant Biology, University of Georgia, Athens, Georgia 30602, USA. Tel: +1 706 542 1832; Fax: +1 706 542 1805; E-mail: zhye@plantbio.uga.edu)
Abstract (Browse 2848)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
An Integrative Analysis of the Effects of Auxin on Jasmonic Acid Biosynthesis in Arabidopsis thaliana  
Author: Jun Liu and Xiu-Jie Wang
Journal of Integrative Plant Biology 2006 48(1)
DOI: 10.1111/j.1744-7909.2006.00206.x
      
    Auxin and jasmonic acid (JA) are two plant phytohormones that both participate in the regulation of many developmental processes. Jasmonic acid also plays important roles in plant stress response reactions. Although extensive investigations have been undertaken to study the biological functions of auxin and JA, little attention has been paid to the cross-talk between their regulated pathways. In the few available reports examining the effects of auxin on the expression of JA or JA-responsive genes, both synergetic and antagonistic results have been found. To further investigate the relationship between auxin and JA, we adopted an integrative method that combines microarray expression data with pathway information to study the behavior of the JA biosynthesis pathway under auxin treatment. Our results showed an overall downregulation of genes involved in JA biosynthesis, providing the first report of a relationship between auxin and the JA synthesis pathway in Arabidopsis seedlings.(Author for correspondence.Institute of Genetics and Development Biology, the Chinese Academy of Sciences, Beijing 100101, China. Tel: +86 (0)10 6484 0941; Fax: +86 (0)10 6487 3428; E-mail: xjwang@genetics.ac.cn)
Abstract (Browse 3247)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Identification and Quantitative Analysis of Significantly Accumulated Proteins During the Arabidopsis Seedling De-etiolation Process  
Author: Bai-Chen Wang, Ying-Hong Pan, Da-Zhe Meng and Yu-Xian Zhu
Journal of Integrative Plant Biology 2006 48(1)
DOI: 10.1111/j.1744-7909.2006.00215.x
      
    Proteomic analysis was performed on seedlings after different light treatments. A total of (1 350㊣31) protein spots was separated and visualized on each silver nitrate-stained two-dimensional gel using protein samples prepared from light-grown or etiolated seedlings with or without 6每9 h light treatment. Twenty-five protein spots (encoded by 19 genes) that were significantly accumulated upon light treatment were identified using the matrix-assisted laser desorption ionization time-of-flight mass spectrometry method. Functional proteomics indicated that these proteins involved mainly in chloroplast development, energy metabolism, cell cycle progression and membrane electron transport. For 18 of the protein-coding genes we identified through an internet search, the transcript levels of 17 genes matched roughly with their protein content in etiolated and green seedlings, suggesting that these genes were regulated by light mainly at the transcriptional level. Despite a very significant increase in the amount of proteins upon light treatment, similar RNA levels were found in dark-grown or green seedlings for the carbonic anhydrase gene At3g05100, indicating a possible post-transcriptional regulatory mechanism. Elucidation of light-induced protein accumulation will undoubtedly enhance our understanding of plant photomorphogenesis.(Author for correspondence.Email: zhuyx@water.pku.edu.cn )
Abstract (Browse 3229)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Parental RNA is Significantly Degraded During Arabidopsis Seed Germination  
Author: Qing Li, Jian-Xun Feng, Pei Han and Yu-Xian Zhu
Journal of Integrative Plant Biology 2006 48(1)
DOI: 10.1111/j.1744-7909.2006.00216.x
      
    Germination is the first and maybe the foremost growth stage in the life cycle of a plant. Herein, we report that initiation of germination in the Arabidopsis Columbia ecotype was accompanied by a sharp decrease in the amount of extractable total RNA. At the beginning of our germination experiment, we were usually able to obtain 35每40 µg total RNA from 100 mg dry seeds. However, after 3 d of cold stratification, we could only obtain less than 5 µg total RNA from the same amount of starting material. Young seedlings contained approximately 100 µg total RNA per 100 mg fresh tissue. Further studies showed that inhibition of de novo RNA synthesis by actinomycin D prevented the degradation of parental RNA and, in the meantime, significantly delayed the germination process. Several ribonuclease-like genes that were highly expressed in dry seeds, and especially during the cold stratification period, were discovered. We propose that these enzymes are involved in the regulation of parental RNA degradation. These results indicate that parental RNA metabolism may be an important process for Arabidopsis seed germination.(Author for correspondence.E-mail:zhuyx@water.pku.edu.cn)
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