July 2012, Volume 54 Issue 7, Pages 434ĘC510.

Cover Caption: Ethylene and Endomembranes
About the cover: Ethylene inhibits the hypocotyl elongation in etiolated Arabidopsis seedlings. Using transmission electron microscopy and genetic analyses, Xu et al. (pp 434ĘC455) show that preventing basal level ethylene responses results in cortical endoplasmic reticulum proliferation, Golgi curvature, and cell wall separation in ein2 hypocotyl cells.


          Cell and Developmental Biology
The Basal Level Ethylene Response is Important to the Wall and Endomembrane Structure in the Hypocotyl Cells of Etiolated Arabidopsis Seedlings
Author: Chan Xu, Xiaoyan Gao, Xiaobin Sun and Chikuang Wen
Journal of Integrative Plant Biology 2012 54(7): 434-455
Published Online: May 17, 2012
DOI: 10.1111/j.1744-7909.2012.01130.x

The sub-cellular events that occur during the ethylene-modulated cell elongation were characterized by examining the ultra-structure of etiolated Arabidopsis seedling hypocotyl cells. Preventing the basal level ethylene response facilitated cell elongation, and the cells exhibited wall loosening and separation phenotype. Nearby the wall separation sites were frequently associated with an increase in the cortical rough endoplasmic reticulum (rER) membranes, the presence of paramural bodies, and the circular Golgi formation. The cortical rER proliferation and circular Golgi phenotype were reverted by the protein biosynthesis inhibitor cycloheximide. The cortical rER membranes were longer when the ethylene response was prevented and shortened with elevated ethylene responses. Proteomic changes between wild type and the ethylene-insensitive mutant ethylene insensitive2 (ein2) seedling hypocotyls indicated that distinct subsets of proteins involving endomembrane trafficking, remodeling, and wall modifications were differentially expressed. FM4-64 staining supported the proteomic changes, which indicated reduced endocytosis activity with alleviation of the ethylene response. The basal level ethylene response has an important role in endomembrane trafficking, biological materials transport and maintenance of the endomembrane organization. It is possible that endomembrane alterations may partly associate with the wall modifications, though the biological significance of the alterations should be addressed in future studies.

Xu C, Gao X, Sun X, Wen CK (2012) The basal level ethylene response is important to the wall and endomembrane structure in the hypocotyl cells of etiolated arabidopsis seedlings. J. Integr. Plant Biol. 54(7), 434–455.

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The Ca2+-dependent DNases are Involved in Secondary Xylem Development in Eucommia ulmoides
Author: Hui-Min Chen, Yu Pang, Jun Zeng, Qi Ding, Shen-Yi Yin, Chao Liu, Meng-Zhu Lu, Ke-Ming Cui and Xin-Qiang He
Journal of Integrative Plant Biology 2012 54(7): 456-470
Published Online: June 13, 2012
DOI: 10.1111/j.1744-7909.2012.01134.x

Secondary xylem development has long been recognized as a typical case of programmed cell death (PCD) in plants. During PCD, the degradation of genomic DNA is catalyzed by endonucleases. However, to date, no endonuclease has been shown to participate in secondary xylem development. Two novel Ca2+-dependent DNase genes, EuCaN1 and EuCaN2, were identified from the differentiating secondary xylem of the tree Eucommia ulmoides Oliv., their functions were studied by DNase activity assay, in situ hybridization, protein immunolocalization and virus-induced gene silencing experiments. Full-length cDNAs of EuCaN1 and EuCaN2 contained an open reading frame of 987 bp, encoding two proteins of 328 amino acids with SNase-like functional domains. The genomic DNA sequence for EuCaN1 had no introns, while EuCaN2 had 8 introns. EuCaN1 and EuCaN2 digested ssDNA and dsDNA with Ca2+-dependence at neutral pH. Their expression was confined to differentiating secondary xylem cells and the proteins were localized in the nucleus. Their activity dynamics was closely correlated with secondary xylem development. Secondary xylem cell differentiation is influenced by RNAi of endonuclease genes. The results provide evidence that the Ca2+-dependent DNases are involved in secondary xylem development.

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          Metabolism and Biochemistry
Arabidopsis Acetyl-Amido Synthetase GH3.5 Involvment in Camalexin Biosynthesis through Conjugation of Indole-3-Carboxylic Acid and Cysteine and Upregulation of Camalexin Biosynthesis Genes  
Author: Mu-Yang Wang, Xue-Ting Liu, Ying Chen, Xiao-Jing Xu, Biao Yu, Shu-Qun Zhang, Qun Li and Zu-Hua He
Journal of Integrative Plant Biology 2012 54(7): 471-485
Published Online: May 25, 2012
DOI: 10.1111/j.1744-7909.2012.01131.x

Camalexin (3-thiazol-2′-yl-indole) is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening and biochemical experiments. Camalexin is formed when indole-3-acetonitrile (IAN) is catalyzed by the cytochrome P450 monooxygenase CYP71A13. Here, we demonstrate that the Arabidopsis GH3.5 protein, a multifunctional acetyl-amido synthetase, is involved in camalexin biosynthesis via conjugating indole-3-carboxylic acid (ICA) and cysteine (Cys) and regulating camalexin biosynthesis genes. Camalexin levels were increased in the activation-tagged mutant gh3.5–1D in both Col-0 and cyp71A13–2 mutant backgrounds after pathogen infection. The recombinant GH3.5 protein catalyzed the conjugation of ICA and Cys to form a possible intermediate indole-3-acyl-cysteinate (ICA(Cys)) in vitro. In support of the in vitro reaction, feeding with ICA and Cys increased camalexin levels in Col-0 and gh3.5–1D. Dihydrocamalexic acid (DHCA), the precursor of camalexin and the substrate for PAD3, was accumulated in gh3.5–1D/pad3–1, suggesting that ICA(Cys) could be an additional precursor of DHCA for camalexin biosynthesis. Furthermore, expression of the major camalexin biosynthesis genes CYP79B2, CYP71A12, CYP71A13 and PAD3 was strongly induced in gh3.5–1D. Our study suggests that GH3.5 is involved in camalexin biosynthesis through direct catalyzation of the formation of ICA(Cys), and upregulation of the major biosynthetic pathway genes.

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          Molecular Physiology
Co-expression Analysis Identifies CRC and AP1 the Regulator of Arabidopsis Fatty Acid Biosynthesis
Author: Xinxin Han, Linlin Yin and Hongwei Xue
Journal of Integrative Plant Biology 2012 54(7): 486-499
Published Online: June 7, 2012
DOI: 10.1111/j.1744-7909.2012.01132.x

Fatty acids (FAs) play crucial rules in signal transduction and plant development, however, the regulation of FA metabolism is still poorly understood. To study the relevant regulatory network, fifty-eight FA biosynthesis genes including de novo synthases, desaturases and elongases were selected as “guide genes” to construct the co-expression network. Calculation of the correlation between all Arabidopsis thaliana (L.) genes with each guide gene by Arabidopsis co-expression dating mining tools (ACT) identifies 797 candidate FA-correlated genes. Gene ontology (GO) analysis of these co-expressed genes showed they are tightly correlated to photosynthesis and carbohydrate metabolism, and function in many processes. Interestingly, 63 transcription factors (TFs) were identified as candidate FA biosynthesis regulators and 8 TF families are enriched. Two TF genes, CRC and AP1, both correlating with 8 FA guide genes, were further characterized. Analyses of the ap1 and crc mutant showed the altered total FA composition of mature seeds. The contents of palmitoleic acid, stearic acid, arachidic acid and eicosadienoic acid are decreased, whereas that of oleic acid is increased in ap1 and crc seeds, which is consistent with the qRT-PCR analysis revealing the suppressed expression of the corresponding guide genes. In addition, yeast one-hybrid analysis and electrophoretic mobility shift assay (EMSA) revealed that CRC can bind to the promoter regions of KCS7 and KCS15, indicating that CRC may directly regulate FA biosynthesis.

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          Plant-environmental Interactions
The C2H2-type Zinc Finger Protein ZFP182 is Involved in Abscisic Acid-Induced Antioxidant Defense in Rice  
Author: Hong Zhang, Lan Ni, Yanpei Liu, Yunfei Wang, Aying Zhang, Mingpu Tan and Mingyi Jiang
Journal of Integrative Plant Biology 2012 54(7): 500-510
Published Online: June 13, 2012
DOI: 10.1111/j.1744-7909.2012.01135.x

C2H2-type zinc finger proteins (ZFPs) are thought to play important roles in modulating the responses of plants to drought, salinity and oxidative stress. However, direct evidence is lacking for the involvement of these ZFPs in abscisic acid (ABA)-induced antioxidant defense in plants. In this study, the role of the rice (Oryza sativa L. sub. japonica cv. Nipponbare) C2H2-type ZFP ZFP182 in ABA-induced antioxidant defense and the relationship between ZFP182 and two rice MAPKs, OsMPK1 and OsMPK5 in ABA signaling were investigated. ABA treatment induced the increases in the expression of ZFP182, OsMPK1 and OsMPK5, and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in rice leaves. The transient gene expression analysis and the transient RNA interference (RNAi) analysis in protoplasts showed that ZFP182, OsMPK1 and OsMPK5 are involved in ABA-induced up-regulation in the activities of SOD and APX. Besides, OsMPK1 and OsMPK5 were shown to be required for the up-regulation in the expression of ZFP182 in ABA signaling, but ZFP182 did not mediate the ABA-induced up-regulation in the expression of OsMPK1 and OsMPK5. These results indicate that ZFP182 is required for ABA-induced antioxidant defense and the expression of ZFP182 is regulated by rice MAPKs in ABA signaling.

Abstract (Browse 1914)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
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