Phase separation of an FtAT-hook transcription factor regulates seed development under heat stress in Tartary buckwheat

Heat stress threatens current crop production systems and food security. The identification and utilization of elite thermotolerance genes and germplasms have emerged as cost-effective strategies to improve the thermotolerance of crops under global warming. This study identified a Tartary buckwheat (Fagopyrum tataricum) high-temperature-induced FtAT-hook transcription factor that undergoes phase separation and negatively controls seed development by increasing the transcript level of the sugar transporter gene FtERDL6 (Early response to dehydration like 6) and key genes for flavonoid synthesis (FtFLS). Additionally, FtASR, an abscisic acid stress-ripening protein, interacted with FtAT-hook to affect the phase separation of FtAT-hook under heat stress. The interaction between FtAT-hook and FtASR was conserved among other species. As a downstream biosynthetic product of FtFLS, kaempferitrin suppresses FtAT-hook phase separation via a negative feedback regulatory mechanism. Notably, the exogenous application of kaempferitrin significantly enhanced the FtASR-FtAT-hook interaction, leading to an increase in seed size under heat stress. These findings provide mechanistic insights into the design of flavonoid compounds to disturb protein phase separation and thereby change its function, and they offer strategies to safeguard food security under global warming.