The role of Arabidopsis heterotrimeric G-protein subunits in MLO2 function and MAMP-triggered immunity.
The role of Arabidopsis heterotrimeric G-protein subunits in MLO2 function and MAMP-triggered immunity.
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DOI：
10.1094/mpmi-03-13-0077-r
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发表时间：
2013-09
期刊：
影响因子：
--
通讯作者：
Panstruga R
中科院分区：
文献类型：
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作者：
Lorek J;Griebel T;Jones AM;Kuhn H;Panstruga R
异三聚体 G 蛋白由 Gα、Gβ 和 Gγ 亚基组成，调节植物中的许多基本过程。尽管如此，植物的 G 蛋白信号传导成分比后生动物要简单得多。在动物中，配体与称为 GPCR 的 7 跨膜 (7TM) 细胞表面受体结合导致 G 蛋白激活，然而，植物 G 蛋白复合物的激活是组成型的，因此植物 7TM 蛋白的确切作用尚不清楚。 MLO 是最具特征性的 7TM 植物蛋白。虽然 MLO2 或 G 蛋白的基因消除会改变对病原体的抵抗力，但尚不清楚 G 蛋白是否直接通过 MLO2 耦合信号传导。在这里，我们利用拟南芥 mlo2 突变体的两种有据可查的表型（广谱白粉病抗性和自发胼胝质沉积）来评估 MLO2 蛋白与 G 蛋白复合物的关系。尽管我们的数据揭示了 Gβ 和 Gγ 亚基对抗真菌防御反应的调节，但我们的研究结果总体上与 MLO2 作为典型 GPCR 的作用不一致。我们发现，Gβ亚基缺陷的突变体在暴露于微生物相关分子模式（MAMP）flg22后表现出防御相关基因子集的延迟积累。此外，Gβ突变体被发现对细菌病原体丁香假单胞菌的喷雾接种高度敏感。总之，我们的数据不支持 MLO 蛋白作为 GPCR 的功能，但揭示了 Gβ 和 Gγ 亚基作为针对生物营养型和半生物营养型植物病原体的基础防御调节剂的作用。
Heterotrimeric G-proteins are composed of Gα, Gβ and Gγ subunits and regulate many fundamental processes in plants. Nonetheless plants have a considerably simpler repertoire of G-protein signaling components than metazoans. In animals, ligand binding to 7 transmembrane (7TM) cell surface receptors designated GPCRs leads to G protein activation, however, activation of the plant G protein complex is constitutive, therefore the exact role of plant 7TM proteins is unclear. MLOs are the best characterized 7TM plant proteins. While genetic ablation of either MLO2 or G proteins alters resistance to pathogens, it is unknown if G proteins directly couple signaling through MLO2. Here we exploited two well-documented phenotypes of Arabidopsis mlo2 mutants, broad-spectrum powdery mildew resistance and spontaneous callose deposition, to assess the relationship of MLO2 proteins to the G protein complex. Although our data reveal modulation of antifungal defence responses by Gβ and Gγ subunits, our findings are overall inconsistent with a role of MLO2 as a canonical GPCR. We discovered that mutants defective in the Gβ subunit show delayed accumulation of a subset of defence-associated genes following exposure to the microbe-associated molecular pattern (MAMP), flg22. Moreover Gβ mutants were found to be hypersusceptible to spray-inoculation with the bacterial pathogen, Pseudomonas syringae. In sum, our data do not support a function for MLO proteins as GPCRs, but unravel a role for Gβ and Gγ subunits as modulators of basal defence against biotrophic and hemibiotrophic phytopathogens.