Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Campus de Montegancedo, E-28223-Pozuelo de Alarcón (Madrid), Spain.
Mol Plant. 2012 Jan;5(1):98-114. doi: 10.1093/mp/ssr082. Epub 2011 Oct 6.
The Arabidopsis heterotrimeric G-protein controls defense responses to necrotrophic and vascular fungi. The agb1 mutant impaired in the Gβ subunit displays enhanced susceptibility to these pathogens. Gβ/AGB1 forms an obligate dimer with either one of the Arabidopsis Gγ subunits (γ1/AGG1 and γ2/AGG2). Accordingly, we now demonstrate that the agg1 agg2 double mutant is as susceptible as agb1 plants to the necrotrophic fungus Plectosphaerella cucumerina. To elucidate the molecular basis of heterotrimeric G-protein-mediated resistance, we performed a comparative transcriptomic analysis of agb1-1 mutant and wild-type plants upon inoculation with P. cucumerina. This analysis, together with metabolomic studies, demonstrated that G-protein-mediated resistance was independent of defensive pathways required for resistance to necrotrophic fungi, such as the salicylic acid, jasmonic acid, ethylene, abscisic acid, and tryptophan-derived metabolites signaling, as these pathways were not impaired in agb1 and agg1 agg2 mutants. Notably, many mis-regulated genes in agb1 plants were related with cell wall functions, which was also the case in agg1 agg2 mutant. Biochemical analyses and Fourier Transform InfraRed (FTIR) spectroscopy of cell walls from G-protein mutants revealed that the xylose content was lower in agb1 and agg1 agg2 mutants than in wild-type plants, and that mutant walls had similar FTIR spectratypes, which differed from that of wild-type plants. The data presented here suggest a canonical functionality of the Gβ and Gγ1/γ2 subunits in the control of Arabidopsis immune responses and the regulation of cell wall composition.
拟南芥异三聚体 G 蛋白控制对坏死和血管真菌的防御反应。在 Gβ亚基中受损的 agb1 突变体对这些病原体的敏感性增强。Gβ/AGB1 与拟南芥 Gγ 亚基（γ1/AGG1 和 γ2/AGG2）之一形成必需的二聚体。因此，我们现在证明 agg1 agg2 双突变体与 agb1 植物一样容易受到坏死真菌 Plectosphaerella cucumerina 的感染。为了阐明异三聚体 G 蛋白介导的抗性的分子基础，我们对 P. cucumerina 接种后 agb1-1 突变体和野生型植物进行了比较转录组分析。这项分析，连同代谢组学研究，表明 G 蛋白介导的抗性独立于对坏死真菌抗性所需的防御途径，例如水杨酸、茉莉酸、乙烯、脱落酸和色氨酸衍生代谢物信号转导，因为这些途径在 agb1 和 agg1 agg2 突变体中没有受损。值得注意的是，agb1 植物中许多失调的基因与细胞壁功能有关，agg1 agg2 突变体也是如此。G 蛋白突变体细胞壁的生化分析和傅里叶变换红外（FTIR）光谱学表明，agb1 和 agg1 agg2 突变体中的木糖含量低于野生型植物，并且突变体细胞壁具有相似的 FTIR 光谱类型，与野生型植物不同。这里提出的数据表明 Gβ和 Gγ1/γ2 亚基在控制拟南芥免疫反应和调节细胞壁组成方面具有典型的功能。
