Heterotrimeric G protein subunits differentially respond to endoplasmic reticulum stress in Arabidopsis

Canonical heterotrimeric G proteins in eukaryotes are major components that localize at plasma membrane and transmit extracellular stimuli into the cell. Genome of a seed plant Arabidopsis thaliana encodes at least one Gα (GPA1), one Gβ (AGB1), and 3 Gγ (AGG1, AGG2 and AGG3) subunits. The loss-of-function mutations of G protein subunit(s) cause multiple defects in development as well as biotic and abiotic stress responses. However, it remains elusive how these subunits differentially express these defects. Here, we report that Arabidopsis heterotrimeric G protein subunits differentially respond to the endoplasmic reticulum (ER) stress. An isolated homozygous mutant of AGB1, agb1-3, was more sensitive to the tunicamycin-induced ER stress compared to the wild type and the other loss-of-function mutants of G protein subunits. Moreover, ER stress responsive genes were highly expressed in the agb1-3 plant. Our results indicate that AGB1 positively contributes to ER stress tolerance in Arabidopsis.

真核生物中的经典异源三聚体G蛋白（heterotrimeric G proteins）是定位于质膜、将胞外刺激信号转导至细胞内的核心组分。种子植物拟南芥（Arabidopsis thaliana）的基因组至少编码1个Gα亚基（GPA1）、1个Gβ亚基（AGB1）以及3个Gγ亚基（AGG1、AGG2与AGG3）。G蛋白亚基的功能丧失突变会导致植株发育、生物胁迫与非生物胁迫响应出现多重缺陷，但目前尚不清楚这些亚基如何差异化介导此类缺陷的产生。本研究发现，拟南芥异源三聚体G蛋白亚基对内质网（endoplasmic reticulum, ER）胁迫存在差异化响应。本研究中分离得到的AGB1纯合突变体agb1-3，相较于野生型及其他G蛋白亚基功能丧失突变体，对衣霉素（tunicamycin）诱导的内质网胁迫更为敏感；且agb1-3植株中内质网胁迫响应基因的表达水平显著上调。本研究结果表明，AGB1对拟南芥的内质网胁迫耐受性具有正向调控作用。