March 2013, Volume 55 Issue 3, Pages 202C289.

Cover Caption: Organization of Actin Filaments
About the cover: Plant actin depolymerizing factor (ADF) binds to both monomeric and filamentous actin, and plays a key role in the organization of the actin cytoskeleton. In this issue, Dong et al. (pp. 250C261) demonstrate that charged residues Arg98 and Lys100 of ADF1 are essential for both G- and F-actin binding, and that basic residues on β-strand 5 (K82/A) and α-helix 4 (R135/A, R137/A) form another actin binding site for F-actin.


H2O2-induced Leaf Cell Death and the Crosstalk of Reactive Nitric/Oxygen Species  
Author: Yiqin Wang, Aihong Lin, Gary J. Loake and Chengcai Chu
Journal of Integrative Plant Biology 2013 55(3): 202-208
Published Online: March 5, 2013
DOI: 10.1111/jipb.12032

In plants, the chloroplast is the main reactive oxygen species (ROS) producing site under high light stress. Catalase (CAT), which decomposes hydrogen peroxide (H2O2), is one of the controlling enzymes that maintains leaf redox homeostasis. The catalase mutants with reduced leaf catalase activity from different plant species exhibit an H2O2-induced leaf cell death phenotype. This phenotype was differently affected by light intensity or photoperiod, which may be caused by plant species, leaf redox status or growth conditions. In the rice CAT mutant nitric oxide excess 1 (noe1), higher H2O2 levels induced the generation of nitric oxide (NO) and higher S-nitrosothiol (SNO) levels, suggesting that NO acts as an important endogenous mediator in H2O2-induced leaf cell death. As a free radical, NO could also react with other intracellular and extracellular targets and form a series of related molecules, collectively called reactive nitrogen species (RNS). Recent studies have revealed that both RNS and ROS are important partners in plant leaf cell death. Here, we summarize the recent progress on H2O2-induced leaf cell death and the crosstalk of RNS and ROS signals in the plant hypersensitive response (HR), leaf senescence, and other forms of leaf cell death triggered by diverse environmental conditions.

Wang Y, Lin A, Loake GJ, Chu C (2013) H2O2-induced leaf cell death and the crosstalk of reactive nitric/oxygen species. J. Integr. Plant Biol. 55(3), 202–208.

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          Cell and Developmental Biology
A Single Amino-Acid Substitution at Lysine 40 of an Arabidopsis thaliana-tubulin Causes Extensive Cell Proliferation and Expansion Defects
Author: Xue Xiong, Deyang Xu, Zhongnan Yang, Hai Huang and Xiaofeng Cui
Journal of Integrative Plant Biology 2013 55(3): 209-220
Published Online: December 7, 2012
DOI: 10.1111/jipb.12003

Microtubules are highly dynamic cytoskeletal polymers of α/β-tubulin heterodimers that undergo multiple post-translational modifications essential for various cellular functions in eukaryotes. The lysine 40 (K40) is largely conserved in α-tubulins in many eukaryote species, and the post-translational modification by acetylation at K40 is critical for neuronal development in vertebrates. However, the biological function of K40 of α-tubulins in plants remains unexplored. In this study, we show in Arabidopsis thaliana that constitutive expression of mutated forms of α-tubulin6 (TUA6) at K40 (TUA6K40A or TUA6K40Q), in which K40 is replaced by alanine or glutamine, result in severely reduced plant size. Phenotypic characterization of the 35S:TUA6K40A transgenic plants revealed that both cell proliferation and cell expansion were affected. Cytological and biochemical analyses showed that the accumulation of α- and β-tubulin proteins was significantly reduced in the transgenic plants, and the cortical microtubule arrays were severely disrupted, indicating that K40 of the plant α-tubulin is critical in maintaining microtubule stability. We also constructed 35S:TUA6K40R transgenic plants in which K40 of the engineered TUA6 protein is replaced by an arginine, and found that the 35S:TUA6K40R plants were phenotypically indistinguishable from the wild-type. Since lysine and arginine are similar in biochemical nature but arginine cannot be acetylated, these results suggest a structural importance for K40 of α-tubulins in cell division and expansion.

Xiong X, Xu D, Yang Z, Huang H, Cui X (2013) A single amino-acid substitution at lysine 40 of an Arabidopsis thaliana α-tubulin causes extensive cell proliferation and expansion defects. J. Integr. Plant Biol. 55(3), 209–220.

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Functional Diversity of CYCLOIDEA-like TCP Genes in the Control of Zygomorphic Flower Development in Lotus japonicus
Author: Shilei Xu, Yonghai Luo, Zhigang Cai, Xiangling Cao, Xiaohe Hu, Jun Yang and Da Luo
Journal of Integrative Plant Biology 2013 55(3): 221-231
Published Online: January 9, 2013
DOI: 10.1111/j.1744-7909.2012.01169.x

CYCLOIDEA (CYC)-like TCP genes play key roles in dorsoventral differentiation of zygomorphic flowers in Papilionoideae legumes. In this study, we analyzed the kew mutants whose flowers lost lateral identity, and investigated the diverse functions of three LjCYC genes during zygomorphic flower development in the model legume Lotus japonicus. We showed that kew1 and kew3 are allelic mutants of LjCYC3, a CYC-like TCP gene. Through transgenic experiments, it was shown that LjCYC1 possesses dorsal activity similar to LjCYC2, and that LjCYC3 alone is sufficient to confer lateral activity, and an epistatic effect between dorsal and lateral activities was identified. Sequence analysis revealed a striking alteration at the 3′ end of the LjCYC3 open reading frame (ORF) in comparison with those of LjCYC1 and LjCYC2 ORFs. Furthermore, it was found that LjCYC proteins could interact with each other and possess different activities by means of a transcriptional activity assay. Our data demonstrate that the sequence variation and the subsequent alteration of protein property play important roles in the functional diversity of different LjCYC genes in controlling zygomorphic flower development in Lotus japonicus.

Xu S, Luo Y, Cai Z, Cao X, Hu X, Yang J, Luo D (2013) Functional diversity of CYCLOIDEA-like TCP genes in the control of zygomorphic flower development in Lotus japonicus. J. Integr. Plant Biol. 55(3), 221–231.

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OsLEC1/OsHAP3E Participates in the Determination of Meristem Identity in Both Vegetative and Reproductive Developments of Rice  
Author: Jing-Jing Zhang and Hong-Wei Xue
Journal of Integrative Plant Biology 2013 55(3): 232-249
Published Online: February 14, 2013
DOI: 10.1111/jipb.12025

In the vegetative phase of plant development, the shoot apical meristem (SAM) produces leaf primordia in regular phyllotaxy, and transforms to the inflorescence meristem when the plant enters reproductive growth, which will undergo a series of identity differentiations and will finally form a complete and fertile panicle. Our previous studies indicated a tissue-specific expression pattern of the OsLEC1 (leafy cotyledon) gene, which is homologous to the Arabidopsis AtLEC1 gene and belongs to the CCAAT-binding protein HAP3 subfamily, during embryo development. Expression of additional OsLEC1 genomic sequences resulted in abnormalities in the development of leaves, panicles and spikelets. The spikelets in particular presented abnormities, including panicle and spikelet-like structures that occurred reiteratively inside prior spikelets, and the occasional spikelet structures that completely transformed into plantlets (a reproductive habit alteration from sexual to asexual called “pseudovivipary”). Analysis showed that OsLEC1 interacts with several SEPALLATA-like MADS transcription factors, suggesting that increased levels of the OsLEC1 protein might interfere with the normal interaction network of these MADS proteins and lead to defective spikelet development. The expression of OsMADS1 was dramatically reduced, and the DNA methylation level of cytosine in certain regions of the OsMADS1 promoter was increased under OsLEC1 overexpression. These results indicate that OsLEC1 affects the development of leaves, panicles and spikelets, and is a key regulator of meristem identity determination in both rice (Oryza sativa) vegetative and reproductive development.

Zhang JJ, Xue HW(2013) OsLEC1/OsHAP3E participates in the determination of meristem identity in both vegetative and reproductive developments of rice. J. Integr. Plant Biol. 55(3), 232–249.

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Arabidopsis AtADF1 is Functionally Affected by Mutations on Actin Binding Sites
Author: Chun-Hai Dong, Wei-Ping Tang and Jia-Yao Liu
Journal of Integrative Plant Biology 2013 55(3): 250-261
Published Online: January 9, 2013
DOI: 10.1111/jipb.12015

The plant actin depolymerizing factor (ADF) binds to both monomeric and filamentous actin, and is directly involved in the depolymerization of actin filaments. To better understand the actin binding sites of the Arabidopsis thaliana L. AtADF1, we generated mutants of AtADF1 and investigated their functions in vitro and in vivo. Analysis of mutants harboring amino acid substitutions revealed that charged residues (Arg98 and Lys100) located at the α-helix 3 and forming an actin binding site together with the N-terminus are essential for both G- and F-actin binding. The basic residues on the β-strand 5 (K82/A) and the α-helix 4 (R135/A, R137/A) form another actin binding site that is important for F-actin binding. Using transient expression of CFP-tagged AtADF1 mutant proteins in onion (Allium cepa) peel epidermal cells and transgenic Arabidopsis thaliana L. plants overexpressing these mutants, we analyzed how these mutant proteins regulate actin organization and affect seedling growth. Our results show that the ADF mutants with a lower affinity for actin filament binding can still be functional, unless the affinity for actin monomers is also affected. The G-actin binding activity of the ADF plays an essential role in actin binding, depolymerization of actin polymers, and therefore in the control of actin organization.

Dong CH, Tang WP, Liu JY (2013) Arabidopsis AtADF1 is functionally affected by mutations on actin binding sites. J. Integr. Plant Biol. 55(3), 250–261.

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          Metabolism and Biochemistry
Physiological and Molecular Features of Puccinellia tenuiflora Tolerating Salt and Alkaline-Salt Stress
Author: Xia Zhang, Liqin Wei, Zizhang Wang and Tai Wang
Journal of Integrative Plant Biology 2013 55(3): 262-276
Published Online: February 4, 2013
DOI: 10.1111/jipb.12013

Saline-alkali soil seriously threatens agriculture productivity; therefore, understanding the mechanism of plant tolerance to alkaline-salt stress has become a major challenge. Halophytic Puccinellia tenuiflora can tolerate salt and alkaline-salt stress, and is thus an ideal plant for studying this tolerance mechanism. In this study, we examined the salt and alkaline-salt stress tolerance of P. tenuiflora, and analyzed gene expression profiles under these stresses. Physiological experiments revealed that P. tenuiflora can grow normally with maximum stress under 600 mmol/L NaCl and 150 mmol/L Na2CO3 (pH 11.0) for 6 d. We identified 4,982 unigenes closely homologous to rice and barley. Furthermore, 1,105 genes showed differentially expressed profiles under salt and alkaline-salt treatments. Differentially expressed genes were overrepresented in functions of photosynthesis, oxidation reduction, signal transduction, and transcription regulation. Almost all genes downregulated under salt and alkaline-salt stress were related to cell structure, photosynthesis, and protein synthesis. Comparing with salt stress, alkaline-salt stress triggered more differentially expressed genes and significantly upregulated genes related to H+ transport and citric acid synthesis. These data indicate common and diverse features of salt and alkaline-salt stress tolerance, and give novel insights into the molecular and physiological mechanisms of plant salt and alkaline-salt tolerance.

Zhang X, Wei L, Wang Z, Wang T (2013) Physiological and molecular features of Puccinellia tenuiflora tolerating salt and alkaline-salt stress. J. Integr. Plant Biol. 55(3), 262–276.

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          Plant-environmental Interactions
Hydrogen Sulfide Regulates Ethylene-induced Stomatal Closure in Arabidopsis thaliana
Author: Zhihui Hou, Lanxiang Wang, Jing Liu, Lixia Hou and Xin Liu
Journal of Integrative Plant Biology 2013 55(3): 277-289
Published Online: February 14, 2013
DOI: 10.1111/jipb.12004

Hydrogen sulfide (H2S) is a newly-discovered signaling molecule in plants and has caused increasing attention in recent years, but its function in stomatal movement is unclear. In plants, H2S is synthesized via cysteine degradation catalyzed by D-/L-cysteine desulfhydrase (D-/L-CDes). AtD-/L-CDes::GUS transgenic Arabidopsis thaliana (L.) Heynh. plants were generated and used to investigate gene expression patterns, and results showed that AtD-/L-CDes can be expressed in guard cells. We also determined the subcellular localization of AtD-/L-CDes using transgenic plants of AtD-/L-CDes::GFP, and the results showed that AtD-CDes and AtL-CDes are located in the chloroplast and in the cytoplasm, respectively. The transcript levels of AtD-CDes and AtL-CDes were affected by the chemicals that cause stomatal closure. Among these factors, ACC, a precursor of ethylene, has the most significant effect, which indicates that the H2S generated from D-/L-CDes may play an important role in ethylene-induced stomatal closure. Meanwhile, H2S synthetic inhibitors significantly inhibited ethylene-induced stomatal closure in Arabidopsis. Ethylene treatment caused an increase of H2S production and of AtD-/L-CDes activity in Arabidopsis leaves. AtD-/L-CDes over-expressing plants exhibited enhanced induction of stomatal closure compared to the wild-type after ethylene treatment; however, the effect was not observed in the Atd-cdes and Atl-cdes mutants. In conclusion, our results suggest that the D-/L-CDes-generated H2S is involved in the regulation of ethylene-induced stomatal closure in Arabidopsis thaliana.

Hou Z, Wang L, Liu J, Hou L, Liu X (2013) Hydrogen sulfide regulates ethylene-induced stomatal closure in Arabidopsis thaliana. J. Integr. Plant Biol. 55(3), 277–289.

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