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 <i>Arabidopsis thaliana</i> encodes at least one Gα (<i>GPA1</i>), one Gβ (<i>AGB1</i>) and three Gγ (<i>AGG1, AGG2</i> and <i>AGG3</i>) 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 <i>AGB1, agb1-3</i>, 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 <i>agb1-3</i> plant. Our results indicate that <i>AGB1</i> positively contribute to ER stress tolerance in Arabidopsis.

真核生物中的经典异源三聚体G蛋白是定位于质膜、将胞外刺激传递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、1个Gβ亚基以及3个Gγ亚基，分别为GPA1、AGB1，以及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地引发此类缺陷。本研究发现，拟南芥异源三聚体G蛋白亚基对内质网（ER）胁迫存在差异化响应。相较于野生型及其他G蛋白亚基功能丧失突变体，纯合的AGB1突变体agb1-3对衣霉素诱导的内质网胁迫更为敏感。此外，内质网胁迫响应基因在agb1-3植株中的表达水平显著升高。本研究结果表明，AGB1正向参与拟南芥的内质网胁迫耐受过程。