SUMOylation of rice DELLA SLR1 modulates transcriptional responses and improves yield under salt stress

DELLA proteins modulate GA signalling and are major regulators of plant plasticity to endure stress. DELLAs are mostly regulated at the post-translational level, and their activity relies on the interaction with upstream regulators and transcription factors (TFs). SUMOylation is a post-translational modification (PTM) capable of changing protein interaction and found to influence DELLA activity in Arabidopsis. We determined that SUMOylation of the single rice DELLA SLENDER RICE1 (SLR1) occurs in a lysine residue different from the one identified in Arabidopsis REPRESSOR OF GA (RGA), which suggests differential DELLA regulation by SUMOylation in monocots and dicots. Remarkably, artificially increasing SUMOylated SLR1 (SUMO1SLR1) levels attenuated the penalty of salt stress on plant yield. Gene expression analysis revealed that the overexpression of SUMOylated SLR1 regulates key dioxygenases that modulate active GA levels, namely GA20ox2 and GA2ox3, which could partially explain the sustained productivity upon salt stress imposition. Besides, SLR1 SUMOylation blocked the interaction with the growth regulator YAB4, which may fine-tune GA20ox2 expression. Mechanistically, we propose that SLR1 SUMOylation disrupts the interaction with members of several transcription factor families to modulate gene expression. We found that SLR1 SUMOylation represents a novel mechanism modulating DELLA activity, which attenuates the impact of stress on plant performance.