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 3 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 contributes to ER stress tolerance in Arabidopsis.

真核生物中的经典异三聚体G蛋白（heterotrimeric G proteins）是定位于质膜、介导胞外刺激信号向胞内传递的关键组分。模式种子植物拟南芥（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型突变会导致植株发育、生物及非生物胁迫响应等多个方面出现缺陷，但目前仍不清楚这些亚基如何差异化调控上述缺陷的发生。本研究发现，拟南芥异三聚体G蛋白亚基对内质网（endoplasmic reticulum, ER）胁迫存在差异化应答反应。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蛋白亚基功能丧失型突变体，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植株中显著高表达。本研究结果表明，AGB1正调控拟南芥对内质网胁迫的耐受性。