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Early View

  Letters to the Editor
Negative regulation of resistance protein©\mediated immunity by master transcription factors SARD1 and CBP60g
Author: Tongjun Sun, Wanwan Liang, Yuelin Zhang and Xin Li
Received: March 16, 2018         Accepted: July 10, 2018
Online Date: July 14, 2018
DOI: 10.1111/jipb.12698
   
      
    

Salicylic acid (SA) is an essential defence hormone in plants. Upon pathogen infection, induced biosynthesis of SA is mediated by Isochorismate synthase 1 (ICS1), whose gene transcription is controlled mainly through two redundant transcription factors, SAR Deficient 1 (SARD1) and Calmodulin©\binding protein 60©\like g (CBP60g). Although these master transcription factors regulate not only positive, but also negative regulators of immunity, how they control signaling events downstream of different immune receptors is unclear. Using autoimmune mutants activating immunity mediated by different receptors we show that, although the sard1 cbp60g double mutant almost fully suppresses the activation of defence mediated by suppressor of npr1©\1, constitutive 2 (snc2), it strikingly enhances snc1, which carries a gain©\of©\function mutation in an intracellular nucleotide©\binding leucine©\rich repeat (NLR) immune receptor. This negative regulation of immunity is achieved through the transcriptional regulation of negative regulators, such as Nudix hydrolase homolog 6 (NUDT6). Our study highlights the diverse roles, especially the negative ones, in the regulation of plant immunity by the two master immune transcription factors SARD1 and CBP60g.

Abstract (Browse 115)   |   References   |   Full Text HTML   |   Full Text PDF       
Essential role of NbNOG1 in ribosomal RNA processing
Author: Jiangbo Guo, Shaojie Han, Jinping Zhao, Cuihua Xin, Xiyin Zheng, Yule Liu, Yan Wang and Feng Qu
Received: April 21, 2018         Accepted: June 21, 2018
Online Date: June 26, 2018
DOI: 10.1111/jipb.12691
   
      
    

Nucleolar GTP©\binding protein 1 (NOG1) is a highly conserved GTPase first reported in Trypanosoma as required for ribosome biogenesis. We characterized NbNOG1, a Nicotiana benthamiana NOG1 ortholog sharing more than 45% amino acid identity with Trypanosoma, yeast, and human NOG1. N. benthamiana plants silenced for NbNOG1 were stunted and produced sterile flowers. NbNOG1 is functionally interchangeable with yeast NOG1 (ScNOG1), rescuing yeast lethality caused by loss of ScNOG1. Finally, NbNOG1 silencing caused over©\accumulation of pre©\rRNA processing intermediates, and concomitant loss of mature rRNAs. Collectively, these data support a role for NbNOG1 in ribosomal RNA processing.

Abstract (Browse 135)   |   References   |   Full Text HTML   |   Full Text PDF       
  Special Issue on Plant Synthetic Biology
On the role of the tricarboxylic acid cycle in plant productivity
Author: Youjun Zhang and Alisdair R. Fernie
Received: June 4, 2018         Accepted: June 18, 2018
Online Date: June 19, 2018
DOI: 10.1111/jipb.12690
   
      
    

The tricarboxylic acid (TCA) cycle is one of the canonical energy pathways of living systems, as well as being an example of a pathway in which dynamic enzyme assemblies, or metabolons, are well characterized. The role of the enzymes have been the subject of saturated transgenesis approaches, whereby the expression of the constituent enzymes were reduced or knocked out in order to ascertain their in vivo function. Some of the resultant plants exhibited improved photosynthesis and plant growth, under controlled greenhouse conditions. In addition, overexpression of the endogenous genes, or heterologous forms of a number of the enzymes, has been carried out in tomato fruit and the roots of a range of species, and in some instances improvement in fruit yield and postharvest properties and plant performance, under nutrient limitation, have been reported, respectively. Given a number of variants, in nature, we discuss possible synthetic approaches involving introducing these variants, or at least a subset of them, into plants. We additionally discuss the likely consequences of introducing synthetic metabolons, wherein certain pairs of reactions are artificially permanently assembled into plants, and speculate as to future strategies to further improve plant productivity by manipulation of the core metabolic pathway.

Abstract (Browse 106)   |   References   |   Full Text HTML   |   Full Text PDF       
  Metabolism and Biochemistry
Efficient iron plaque formation on tea (Camellia sinensis) roots contributes to acidic stress tolerance
Author: Xianchen Zhang, Honghong Wu, Lingmu Chen, Yeyun Li, Xiaochun Wan
Received: April 26, 2018         Accepted: July 19, 2018
Online Date: July 23, 2018
DOI: 10.1111/jipb.12702
   
      
    

Tea plants grow in acidic soil, but to date, their intrinsic mechanisms of acidic stress tolerance have not been elucidated. Here, we assessed the tea plant response to growth on NH4+ nutrient media having different pH and iron levels. When grown in standard NH4+ nutrient solution (iron insufficient, 0.35 mg L−1Fe2+), tea roots exhibited significantly lower nitrogen accumulation, plasma membrane H+©\ATPase activity, and protein levels; net H+ efflux was lower at pH 4.0 and 5.0 than at pH 6.0. Addition of 30 mg L−1Fe2+ (iron sufficient, mimicking normal soil Fe2+ concentrations) to the NH4+ nutrient solution led to more efficient iron plaque formation on roots and increased root plasma membrane H+©\ATPase levels and activities at pH 4.0 and 5.0, compared to the pH 6.0 condition. Furthermore, plants grown at pH 4.0 and 5.0, with sufficient iron, exhibited significantly higher nitrogen accumulation than those grown at pH 6.0. Together, these results support the hypothesis that efficient iron plaque formation, on tea roots, is important for acidic stress tolerance. Furthermore, our findings establish that efficient iron plaque formation is linked to increased levels and activities of the tea root plasma membrane H+©\ATPase, under low pH conditions.

Abstract (Browse 80)   |   References   |   Full Text HTML   |   Full Text PDF       
Crystal structure of Arabidopsis thaliana RabA1a
Author: Ji-Sook Yun, Sung Chul Ha, Shinae Kim, Yeon-Gil Kim, Hyeran Kim, and Jeong Ho Chang
Received: May 15, 2018         Accepted: July 11, 2018
Online Date: July 16, 2018
DOI: 10.1111/jipb.12700
   
      
    

RabGTPase is a member of the Ras superfamily of small GTPases, which share a GTP©\binding pocket containing highly conserved motifs that promote GTP hydrolysis. In Arabidopsis, the RabA group, which corresponds to the Rab11 group in animals, functions in the recycling of endosomes that control docking and fusion during vesicle transport. However, their molecular mechanisms remain unknown. In this study, we determined the crystal structures of the GDP©\bound inactive form and both GppNHp©\ and GTP©\bound active forms of RabA1a, at resolutions of 2.8, 2.6, and 2.6 Å, respectively. A bound sulfate ion in the active site of the GDP©\bound structure stabilized Switch II by bridging the interaction between a magnesium ion and Arg74. Comparisons of the two states of RabA1a with Rab11 proteins revealed clear differences in the Switch I and II loops. These results suggested that conformational change of the Switch regions of RabA1a, derived by GTP or GDP binding, could maintain subcellular membrane traffic through the specific interaction of effector molecules.

Abstract (Browse 83)   |   References   |   Full Text HTML   |   Full Text PDF       
  Cell and Developmental Biology
Rab©\H1b is essential for trafficking of cellulose synthase and for hypocotyl growth in Arabidopsis thaliana
Author: Ming He, Miao Lan, Baocai Zhang, Yihua Zhou, Youqun Wang, Lei Zhu, Ming Yuan, and Ying Fu
Received: April 22, 2018         Accepted: July 3, 2018
Online Date: July 5, 2018
DOI: 10.1111/jipb.12694
   
      
    

Cell©\wall deposition of cellulose microfibrils is essential for plant growth and development. In plant cells, cellulose synthesis is accomplished by cellulose synthase complexes located in the plasma membrane. Trafficking of the complex between endomembrane compartments and the plasma membrane is vital for cellulose biosynthesis; however, the mechanism for this process is not well understood. We here report that, in Arabidopsis thaliana, Rab©\H1b, a Golgi©\localized small GTPase, participates in the trafficking of CELLULOSE SYNTHASE 6 (CESA6) to the plasma membrane. Loss of Rab©\H1b function resulted in altered distribution and motility of CESA6 in the plasma membrane and reduced cellulose content. Seedlings with this defect exhibited short, fragile etiolated hypocotyls. Exocytosis of CESA6 was impaired in rab©\h1b cells, and endocytosis in mutant cells was significantly reduced as well. We further observed accumulation of vesicles around an abnormal Golgi apparatus having an increased number of cisternae in rab©\h1b cells, suggesting a defect in cisternal homeostasis caused by Rab©\H1b loss function. Our findings link Rab GTPases to cellulose biosynthesis, during hypocotyl growth, and suggest Rab©\H1b is crucial for modulating the trafficking of cellulose synthase complexes between endomembrane compartments and the plasma membrane and for maintaining Golgi organization and morphology.

Abstract (Browse 103)   |   References   |   Full Text HTML   |   Full Text PDF       
OsPKp¦Á1 encodes a plastidic pyruvate kinase that affects starch biosynthesis in the rice endosperm
Author: Yue Cai, Wenwei Zhang, Jie Jin, Xiaoming Yang, Xiaoman You, Haigang Yan, Liang Wang, Jie Chen, Jiahuan Xu, Weiwei Chen, Xingang Chen, Jing Ma, Xiaojie Tang, Fei Kong, Xiaopin Zhu, Guoxiang Wang, Ling Jiang, William Terzaghi, Chunming Wang and Jianmin Wan
Received: March 14, 2018         Accepted: June 25, 2018
Online Date: June 26, 2018
DOI: 10.1111/jipb.12692
   
      
    

Pyruvate kinase (PK) is a key enzyme in glycolysis and carbon metabolism. Here, we isolated a rice (Oryza sativa) mutant, w59, with a white©\core floury endosperm. Map©\based cloning of w59 identified a mutation in OsPKpα1, which encodes a plastidic isoform of PK (PKp). OsPKpα1 localizes to the amyloplast stroma in the developing endosperm, and the mutation of OsPKpα1 in w59 decreases the plastidic PK activity, resulting in dramatic changes to the lipid biosynthesis in seeds. The w59 grains were also characterized by a marked decrease in starch content. Consistent with a decrease in number and size of the w59 amyloplasts, large empty spaces were observed in the central region of the w59 endosperm, at the early grain©\filling stage. Moreover, a phylogenetic analysis revealed four potential rice isoforms of OsPKp. We validated the in vitro PK activity of these OsPKps through reconstituting active PKp complexes derived from inactive individual OsPKps, revealing the heteromeric structure of rice PKps, which was further confirmed using a protein–protein interaction analysis. These findings suggest a functional connection between lipid and starch synthesis in rice endosperm amyloplasts.

Abstract (Browse 104)   |   References   |   Full Text HTML   |   Full Text PDF       
Proteome analysis of peroxisomes from dark©\treated senescent Arabidopsis leaves
Author: Ronghui Pan, Sigrun Reumann, Piotr Lisik, Stefanie Tietz, Laura J. Olsen and Jianping Hu
Received: May 8, 2018         Accepted: May 29, 2018
Online Date: June 7, 2018
DOI: 10.1111/jipb.12670
   
      
    

Peroxisomes compartmentalize a dynamic suite of biochemical reactions and play a central role in plant metabolism, such as the degradation of hydrogen peroxide, metabolism of fatty acids, photorespiration, and the biosynthesis of plant hormones. Plant peroxisomes have been traditionally classified into three major subtypes, and in©\depth mass spectrometry (MS)©\based proteomics has been performed to explore the proteome of the two major subtypes present in green leaves and etiolated seedlings. Here, we carried out a comprehensive proteome analysis of peroxisomes from Arabidopsis leaves given a 48©\h dark treatment. Our goal was to determine the proteome of the third major subtype of plant peroxisomes from senescent leaves, and further catalog the plant peroxisomal proteome. We identified a total of 111 peroxisomal proteins and verified the peroxisomal localization for six new proteins with potential roles in fatty acid metabolism and stress response by in vivo targeting analysis. Metabolic pathways compartmentalized in the three major subtypes of peroxisomes were also compared, which revealed a higher number of proteins involved in the detoxification of reactive oxygen species in peroxisomes from senescent leaves. Our study takes an important step towards mapping the full function of plant peroxisomes.

Abstract (Browse 111)   |   References   |   Full Text HTML   |   Full Text PDF       
  Plant-abiotic Interactions
    No data
  Invited Expert Review
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  Molecular Physiology
The central circadian clock proteins CCA1 and LHY regulate iron homeostasis in Arabidopsis
Author: Gang Xu, Zhimin Jiang, Haiyang Wang and Rongcheng Lin
Received: May 4, 2018         Accepted: July 6, 2018
Online Date: July 10, 2018
DOI: 10.1111/jipb.12696
   
      
    

Circadian clock is the endogenous time©\keeping machinery that synchronizes an organism's metabolism, behavior, and physiology to the daily light©\dark circles, thereby contributing to organismal fitness. Iron (Fe) is an essential micronutrient for all organisms and it plays important roles in diverse processes of plant growth and development. Here, we show that, in Arabidopsis thaliana, loss of the central clock genes, CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), results in both reduced Fe uptake and photosynthetic efficiency, whereas CCA1 overexpression confers the opposite effects. We show that root Fe(III) reduction activity, and expression of FERRIC REDUCTION OXIDASE 2 (FRO2) and IRON©\REGULATED TRANSPORTER 1 (IRT1) exhibit circadian oscillations, which are disrupted in the cca1 lhy double mutant. Furthermore, CCA1 directly binds to the specific regulatory regions of multiple Fe homeostasis genes and activates their expression. Thus, this study established that, in plants, CCA1 and LHY function as master regulators that maintain cyclic Fe homeostasis.

Abstract (Browse 107)   |   References   |   Full Text HTML   |   Full Text PDF       
Alleviation by abscisic acid of Al toxicity in rice bean is not associated with citrate efflux but depends on ABI5©\mediated signal transduction pathways
Author: Wei Fan, Jia Meng Xu, Pei Wu, Zhi Xin Yang, He Qiang Lou, Wei Wei Chen, Jian Fen Jin, Shao Jian Zheng and Jian Li Yang
Received: April 14, 2018         Accepted: July 4, 2018
Online Date: July 5, 2018
DOI: 10.1111/jipb.12695
   
      
    

Under conditions of aluminum (Al) toxicity, which severely inhibits root growth in acidic soils, plants rapidly alter their gene expression to optimize physiological fitness for survival. Abscisic acid (ABA) has been suggested as a mediator between Al stress and gene expression, but the underlying mechanisms remain largely unknown. Here, we investigated ABA©\mediated Al©\stress responses, using integrated physiological and molecular biology approaches. We demonstrate that Al stress caused ABA accumulation in the root apex of rice bean (Vigna umbellata [Thunb.] Ohwi & Ohashi), which positively regulated Al tolerance. However, this was not associated with known Al©\tolerance mechanisms. Transcriptomic analysis revealed that nearly one©\third of the responsive genes were shared between the Al©\stress and ABA treatments. We further identified a transcription factor, ABI5, as being positively involved in Al tolerance. Arabidopsis abi5 mutants displayed increased sensitivity to Al, which was not related to the regulation of AtALMT1 and AtMATE expression. Functional categorization of ABI5©\mediated genes revealed the importance of cell wall modification and osmoregulation in Al tolerance, a finding supported by osmotic stress treatment on Al tolerance. Our results suggest that ABA signal transduction pathways provide an additional layer of regulatory control over Al tolerance in plants.

Abstract (Browse 90)   |   References   |   Full Text HTML   |   Full Text PDF       
  Functional Omics and Systems Biology
Genome©\wide screening of long non©\coding RNAs involved in rubber biosynthesis in Eucommia ulmoides  
Author: Huimin Liu, Yan Lu, Juan Wang, Jingjing Hu, Tana Wuyun
Received: March 2, 2018         Accepted: June 25, 2018
Online Date: June 26, 2018
DOI: 10.1111/jipb.12693
   
      
    

Increasing evidence indicates that long non©\coding RNAs (lncRNAs) play pivotal roles in regulatory networks controlling plant and animal gene expression. However, lncRNA roles in regulating rubber biosynthesis in Eucommia ulmoides, an emerging source of natural rubber (Eu©\rubber), are currently unknown. Here, we report on RNA deep©\sequencing of E. ulmoides fruits at two developmental stages. Based on application of a stringent pipeline, 29,103 lncRNAs and 9,048 transcripts of uncertain coding potential (TUCPs) were identified. Two differentially expressed (DE) TUCPs appear to simultaneously regulate 12 protein©\coding genes involved in Eu©\rubber biosynthesis (GIEBs), as well as 95 DE genes. Functional categorization of these 95 DE genes indicated their involvement in subcellular microstructures and cellular processes, such as cell wall, cell division, and growth. These DE genes may participate in the differentiation and development of laticifers, where Eu©\rubber is synthesized. A model is proposed in which “commanders” (DE TUCPs) direct the “builders” (DE genes) to construct a “storehouse” of materials needed for Eu©\rubber synthesis, and the “workers” (GIEBs) to synthesize Eu©\rubber. These findings provide insights into both cis©\ and trans©\polyisoprene biosynthesis in plants, laying the foundation for additional studies of this crucial process.

Abstract (Browse 114)   |   References   |   Full Text HTML   |   Full Text PDF       
  Molecular Ecology and Evolution
Tecia solanivora infestation increases tuber starch accumulation in Pastusa Suprema potatoes
Author: Pavan Kumar, Etzel Garrido, Kun Zhao, Yi Zheng, Saleh Alseekh, Erandi Vargas-Ortiz, Alisdair R. Fernie, Zhangjun Fei, Katja Poveda and Georg Jander
Received: May 4, 2018         Accepted: June 7, 2018
Online Date: June 11, 2018
DOI: 10.1111/jipb.12675
   
      
    

In response to infestation with larvae of the Guatemalan tuber moth (Tecia solanivora), some Solanum tuberosum (potato) varieties exhibit an overcompensation response, whereby the total dry mass of uninfested tubers is increased. Here, we describe early responses, within the first few days, of T. solanivora feeding, in the Colombian potato variety Pastusa Suprema. Non©\targeted metabolite profiling showed significant secondary metabolism changes in T. solanivora©\infested tubers, but not in uninfested systemic tubers. In contrast, changes in primary metabolism were greater in uninfested systemic tubers than in the infested tubers, with a notable 80% decline in systemic tuber sucrose levels within 1 d of T. solanivora infestation. This suggested either decreased sucrose transport from the leaves or increased sink strength, i.e., more rapid sucrose to starch conversion in the tubers. Increased sucrose synthesis was indicated by higher rubisco activase and lower starch synthase gene expression in the leaves of infested plants. Elevated sink strength was demonstrated by 45% more total starch deposition in systemic tubers of T. solanivora©\infested plants compared to uninfested control plants. Thus, rather than investing in increased defense of uninfested tubers, Pastusa Suprema promotes deposition of photoassimilates in the form of starch as a response to T. solanivora infestation.

Abstract (Browse 119)   |   References   |   Full Text HTML   |   Full Text PDF       

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