University of North Carolina Chapel Hill, North Carolina
Body of Abstract: Salicylic acid (SA) and Jasmonic acid (JA) antagonism balances the plant growth-defense trade-off. Heterotrimeric Gα-Gβ-Gγ proteins are hubs that regulate SA and JA defense signaling. The Gα (GPA1) and Gβ subunit (AGB1) is required for defense against biotrophic (GPA1) and necrotrophic (AGB1) pathogens. We found that GPA1 and AGB1 protein interact in vivo with TCP14 and JAZ3, transcriptional regulators of SA and JA, respectively, and thereby control their sub-nuclear accumulation. GPA1 slows the proteasomal degradation of AGB1-TCP14-JAZ3 normally driven by both JA and the virulence effector HopBB1, thus boosting SA-based defense. GPA1 activity is regulated by JA-induced phosphorylation of multiple highly conserved residues located in its αE-helix, near the nucleotide-binding pocket, and within the N-terminal α-helix. The relevant phosphomimic mutants, do not affect GTP binding or hydrolysis, but favor GPA1 interaction with TCP14/JAZ3, thereby preventing their degradation. This additional mechanism of de-sequestering G protein partners to affect transcriptional regulation may extend to both yeast and human cells.