SIZ1-mediated SUMOylation of HAT1 enhances plant thermotolerance in Arabidopsis.

Heat stress poses a great threat to plant survival. Although great progress has been made in identifying multiple important regulatory factors in response to heat stress, the post-translational regulatory mechanisms in the process are largely unknown. SUMOylation is an important post-translational modification of proteins and plays key roles in the heat stress response. Here, we identified HAT1 as a novel substrate of SUMO E3 ligase SAPAND MIZ1DOMAIN-CONTAINING LIGASE1 (SIZ1). Further analysis revealed that high temperature induces the accumulation of the SIZ1 protein, which promotes its interaction with HAT1 and SUMOylation of HAT1, thereby facilitating the degradation of HAT1. Moreover, HAT1 can directly bind to the promoters of heat shock proteins to suppress their transcriptional activity. Thereby, SIZ1 mediates the SUMOylation of HAT1 to inhibit the repression of HAT1 on the expression of heat shock proteins under heat stress, thereby positively regulating heat tolerance. Taken together, our findings prove a new molecular module SIZ1-HAT1 by which plants dynamically regulate heat stress response and identify HAT1 as a brake to prevent excessive heat stress response. It provides referenceable theoretical knowledge and highly promising molecular targets for the future development of smart crops with coordinated enhancement of growth and thermotolerance.