Arabidopsis extra large G-protein 2 (XLG2) interacts with the Gbeta subunit of heterotrimeric G protein and functions in disease resistance.
Arabidopsis extra large G-protein 2 (XLG2) interacts with the Gbeta subunit of heterotrimeric G protein and functions in disease resistance.
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DOI：
10.1093/mp/ssp001
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发表时间：
2009-05
期刊：
影响因子：
27.5
通讯作者：
Huifen Zhu;Guojing Li;L. Ding;Xiangqin Cui;H. Berg;S. Assmann;Yiji Xia
中科院分区：
文献类型：
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作者：
Huifen Zhu;Guojing Li;L. Ding;Xiangqin Cui;H. Berg;S. Assmann;Yiji Xia
异三聚体gtp结合蛋白由Galpha， Gbeta和gamma亚基组成，在将细胞表面受体感知的细胞外信号转导为细胞内生理反应中发挥重要作用。除了一种典型的半胱甘肽蛋白（GPA1）外，拟南芥还具有三种独特的半胱甘肽样蛋白，即XLG1、XLG2和XLG3，它们被发现定位于细胞核中，尽管它们的功能和作用方式在很大程度上仍然未知。通过转录组学分析，我们发现XLG2和XLG3在感染丁香假单胞菌后能快速诱导，而XLG1的转录水平不受病原菌感染的影响。反向遗传筛选显示，xlg2功能缺失突变导致对丁香假单胞菌的易感性增强。转录组分析显示，xlg2突变影响病原体触发的一小部分防御相关基因的诱导。而xlg1和xlg3突变体对紫丁香假单胞菌的抗性与野生型没有差异。此外，xlg2 xlg3双突变体和xlg1 xlg2 xlg3三突变体在抗病表型上与xlg2单突变体没有显著差异，这表明xlg1和xlg3在防御中的作用，如果有的话，不如xlg2显著。XLG2的组成性过表达导致多个防御相关基因的异常转录物的积累。通过共免疫沉淀试验，XLG2被发现与AGB1相互作用，AGB1是拟南芥中唯一的Gbeta亚基，之前被发现是对坏死性真菌病原体抗性的正调节因子。而3个xlg单突变体、xlg2、xlg3双突变体、xlg3三突变体和野生型植物对坏死性真菌病原菌灰霉病菌（Botrytis cinerea）和油菜互花菌（Alternaria brassicola）的抗性无显著差异。这些结果表明，XLG2和AGB1是不同于典型异源三聚体g蛋白复合物的组分，可能在调节防御反应中具有不同的功能。
Heterotrimeric GTP-binding proteins, which consist of Galpha, Gbeta, and Ggamma subunits, play important roles in transducing extracellular signals perceived by cell surface receptors into intracellular physiological responses. In addition to a single prototypical Galpha protein (GPA1), Arabidopsis has three unique Galpha-like proteins, known as XLG1, XLG2, and XLG3, that have been found to be localized in nuclei, although their functions and mode of action remain largely unknown. Through a transcriptomic analysis, we found that XLG2 and XLG3 were rapidly induced by infection with the bacterial pathogen Pseudomonas syringae, whereas the XLG1 transcript level was not affected by pathogen infection. A reverse genetic screen revealed that the xlg2 loss-of-function mutation causes enhanced susceptibility to P. syringae. Transcriptome profiling revealed that the xlg2 mutation affects pathogen-triggered induction of a small set of defense-related genes. However, xlg1 and xlg3 mutants showed no difference from wild-type plants in resistance to P. syringae. In addition, the xlg2 xlg3 double mutant and the xlg1 xlg2 xlg3 triple mutant were not significantly different from the xlg2 single mutant in the disease resistance phenotype, suggesting that the roles of XLG1 and XLG3 in defense, if any, are less significant than for XLG2. Constitutive overexpression of XLG2 leads to the accumulation of abnormal transcripts from multiple defense-related genes. Through co-immunoprecipitation assays, XLG2 was found to interact with AGB1, the sole Gbeta subunit in Arabidopsis, which has previously been found to be a positive regulator in resistance to necrotrophic fungal pathogens. However, no significant difference was found between three xlg single mutants, the xlg2 xlg3 double mutant, the xlg triple mutant, and wild-type plants in resistance to the necrotrophic fungal pathogens Botrytis cinerea or Alternaria brassicicola. These results suggest that XLG2 and AGB1 are components of a G-protein complex different from the prototypical heterotrimeric G-protein and may have distinct functions in modulating defense responses.