March 2012, Volume 54 Issue 3, Pages 134C207.

Cover Caption: Cytosolic Localization of GLYR1
About the cover: Glyoxylate reductase isoform 1 (GLYR1) is a key enzyme in the -aminobutryate (GABA) pathway that is linked to a remarkable array of biological processes including stress response, signaling, and redox homeostasis. However, previously the intracellular localization of GLYR1 was unclear. Ching et al. (pp 152C168) show that GLYR1 in plant cells is localized to the cytosol and not peroxisomes, as previously proposed, by using Arabidopsis mesophyll cells co-expressing GFP-tagged GLYR1 and a Cherry-tagged peroxisomal protein.


          Invited Expert Reviews
Disease Resistance in Maize and the Role of Molecular Breeding in Defending Against Global Threat  
Author: Farhan Ali and Jianbing Yan
Journal of Integrative Plant Biology 2012 54(3): 134-151
Published Online: March 19, 2012
DOI: 10.1111/j.1744-7909.2012.01105.x

Diseases are a potential threat to global food security but plants have evolved an extensive array of methodologies to cope with the invading pathogens. Non-host resistance and quantitative resistance are broad spectrum forms of resistance, and all kinds of resistances are controlled by extremely diverse genes called “R-genes”. R-genes follow different mechanisms to defend plants and PAMP-induced defenses in susceptible host plants are referred to as basal resistance. Genetic and phenotypic diversity are vital in maize (Zea mays L.); as such, genome wide association study (GWAS) along with certain other methodologies can explore the maximum means of genetic diversity. Exploring the complete genetic architecture to manipulate maize genetically reduces the losses from hazardous diseases. Genomic studies can reveal the interaction between different genes and their pathways. By confirming the specific role of these genes and protein-protein interaction (proteomics) via advanced molecular and bioinformatics tools, we can shed a light on the most complicated and abstruse phenomena of resistance.

Ali F, Yan J (2012) Disease resistance in maize and the role of molecular breeding in defending against global threat. J. Integr. Plant Biol. 54(3), 134–151.

Abstract (Browse 2244)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Cell and Developmental Biology
Glyoxylate Reductase Isoform 1 is Localized in the Cytosol and Not Peroxisomes in Plant Cells
Author: Steven L. K. Ching, Satinder K. Gidda1, Amanda Rochon, Owen R. van Cauwenberghe, Barry J. Shelp and Robert T. Mullen
Journal of Integrative Plant Biology 2012 54(3): 152-168
Published Online: February 6, 2012
DOI: 10.1111/j.1744-7909.2012.01103.x

Glyoxylate reductase (GLYR) is a key enzyme in plant metabolism which catalyzes the detoxification of both photorespiratory glyoxylate and succinic semialdehdye, an intermediate of the γ-aminobutyrate (GABA) pathway. Two isoforms of GLYR exist in plants, GLYR1 and GLYR2, and while GLYR2 is known to be localized in plastids, GLYR1 has been reported to be localized in either peroxisomes or the cytosol. Here, we reappraised the intracellular localization of GLYR1 in Arabidopsis thaliana L. Heynh (ecotype Lansberg erecta) using both transiently-transformed suspension cells and stably-transformed plants, in combination with fluorescence microscopy. The results indicate that GLYR1 is localized exclusively to the cytosol regardless of the species, tissue and/or cell type, or exposure of plants to environmental stresses that would increase flux through the GABA pathway. Moreover, the C-terminal tripeptide sequence of GLYR1, -SRE, despite its resemblance to a type 1 peroxisomal targeting signal, is not sufficient for targeting to peroxisomes. Collectively, these results define the cytosol as the intracellular location of GLYR1 and provide not only important insight to the metabolic roles of GLYR1 and the compartmentation of the GABA and photorespiratory pathways in plant cells, but also serve as a useful reference for future studies of proteins proposed to be localized to peroxisomes and/or the cytosol.

Ching SLK, Gidda SK, Rochon A, van Cauwenberghe OR, Shelp BJ, Mullen RT (2012) Glyoxylate reductase isoform 1 is localized in the cytosol and not peroxisomes in plant cells. J. Integr. Plant Biol. 54(3), 152–168.

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          Plant-environmental Interactions
ROP11 GTPase is a Negative Regulator of Multiple ABA Responses in Arabidopsis  
Author: Zixing Li, Jun Kang, Ning Sui and Dong Liu
Journal of Integrative Plant Biology 2012 54(3): 169-179
Published Online: January 10, 2012
DOI: 10.1111/j.1744-7909.2012.01100.x

The phytohormone abscisic acid (ABA) plays crucial roles in plant development and plant responses to environmental stresses. Although ABA receptors and a minimal set of core molecular components have recently been discovered, understanding of the ABA signaling pathway is still far from complete. In this work, we characterized the function of ROP11, a member of the plant-specific ROP small GTPases family, in the ABA signaling process. ROP11 is preferentially expressed in guard cells in all plant organs with stomata. Expression of a constitutively active ROP11 (CA-ROP11) suppresses ABA-mediated responses, whereas reduced expression of ROP11 or expression of its dominant-negative form (DN-ROP11) causes the opposite phenotypes. The affected ABA-mediated responses by ROP11 include seed germination, seedling growth, stomatal closure, induction of ABA-responsive genes, as well as plant response to drought stress. Furthermore, we showed that ROP11 and its closest-related family member, ROP10, act in parallel in mediating these responses. ABA treatment does not affect ROP11 transcription and protein abundance; however, it causes the accumulation of CA-ROP11 in the nucleus. These results demonstrated that ROP11 is a negative regulator of multiple ABA responses in Arabidopsis.

Li Z, Kang J, Sui N, Liu D (2012) ROP11 GTPase is a negative regulator of multiple ABA responses in Arabidopsis. J. Integr. Plant Biol. 54(3),169–179.

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ROP11 GTPase Negatively Regulates ABA Signaling by Protecting ABI1 Phosphatase Activity from Inhibition by the ABA Receptor RCAR1/PYL9 in Arabidopsis
Author: Zixing Li, Zheng Li, Xiang Gao, Viswanathan Chinnusamy, Ray Bressan, Zhi-Xin Wang, Jian-Kang Zhu, Jia-Wei Wu and Dong Liu
Journal of Integrative Plant Biology 2012 54(3): 180-188
Published Online: January 18, 2012
DOI: 10.1111/j.1744-7909.2012.01101.x

The phytohormone abscisic acid (ABA) regulates many key processes in plants, such as seed germination, seedling growth, and abiotic stress tolerance. In recent years, a minimal set of core components of a major ABA signaling pathway has been discovered. These components include a RCAR/PYR/PYL family of ABA receptors, a group of PP2C phosphatases, and three SnRK2 kinases. However, how the interactions between the receptors and their targets are regulated by other proteins remains largely unknown. In a companion paper published in this issue, we showed that ROP11, a member of the plant-specific Rho-like small GTPase family, negatively regulates multiple ABA responses in Arabidopsis. The current work demonstrated that the constitutively active ROP11 (CA-ROP11) can modulate the RCAR1/PYL9-mediated ABA signaling pathway based on reconstitution assays in protoplasts. Furthermore, using luciferase complementation imaging, yeast two-hybrid assays, coimmunoprecipitation assays, and bimolecular fluorescence complementation assays, we
demonstrated that CA-ROP11 directly interacts with ABI1, a signaling component downstream of RCAR1/PYL9. Finally, we provided biochemical evidence that CAROP11 protects ABI1 phosphatase activity from inhibition by RCAR1/PYL9 and thus negatively regulates ABA signaling in plant cells. A model of how ROP11 acts to negatively regulate ABA signaling is presented.

Li Z, Li Z, Gao X, Chinnusamy V, Bressan R, Wang ZX, Zhu JK, Wu JW, Liu D (2012) ROP11 GTPase negatively regulates ABA signaling by protecting ABI1 phosphatase activity from inhibition by the ABA receptor RCAR1/PYL9 in Arabidopsis. J. Integr. Plant Biol. 54(3), 180–188.

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DICER-like Proteins and Their Role in Plant-herbivore Interactions in Nicotiana attenuata
Author: Tohir Ahmadovich Bozorov, Shree Prakash Pandey, Son Truong Dinh, Sang-Gyu Kim, Maria Heinrich, Klaus Gase and Ian T. Baldwin
Journal of Integrative Plant Biology 2012 54(3): 189-206
Published Online: February 7, 2012
DOI: 10.1111/j.1744-7909.2012.01104.x

DICER-like (DCL) proteins produce small RNAs that silence genes involved in development and defenses against viruses and pathogens. Which DCLs participate in plant-herbivore interactions remains unstudied. We identified and stably silenced four distinct DCL genes by RNAi in Nicotiana attenuata (Torrey ex. Watson), a model for the study of plant-herbivore interactions. Silencing DCL1 expression was lethal. Manduca sexta larvae performed significantly better on ir-dcl3 and ir-dcl4 plants, but not on ir-dcl2 plants compared to wild type plants. Phytohormones, defense metabolites and microarray analyses revealed that when DCL3 and DCL4 were silenced separately, herbivore resistance traits were regulated in distinctly different ways. Crossing of the lines revealed complex interactions in the patterns of regulation. Single ir-dcl4 and double ir-dcl2 ir-dcl3 plants were impaired in JA accumulation, while JA-Ile was increased in ir-dcl3 plants. Ir-dcl3 and ir-dcl4 plants were impaired in nicotine accumulation; silencing DCL2 in combination with either DCL3 or DCL4 restored nicotine levels to those of WT. Trypsin proteinase inhibitor activity and transcripts were only silenced in ir-dcl3 plants. We conclude that DCL2/3/4 interact in a complex manner to regulate anti-herbivore defenses and that these interactions significantly complicate the already challenging task of understanding smRNA function in the regulation of biotic interactions.

Bozorov TA, Pandey SP, Dinh ST, Kim SG, Heinrich M, Gase K, Baldwin IT (2012) Dicer-like proteins and their role in plant-herbivore interactions in Nicotiana attenuata. J. Integr. Plant Biol. 54(3), 189–206.

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