FtbHLH1, a transcription factor that interacts with FtATG8a, enhances the drought stress response in Tartary buckwheat

Tartary buckwheat (Fagopyrum tataricum) is a traditional cereal crop cultivated in hilly, arid, cool mountainous regions. The bHLH transcription factors play a pivotal role in regulating flavonoid metabolism and enhancing resistance to extreme environments in Tartary buckwheat. However, the functional characterization of bHLH genes in this species remains incomplete. Previous research identified FtbHLH1 as an interacting partner of the key autophagy protein FtATG8a through yeast library screening. Yeast two-hybrid, bimolecular fluorescence complementation, and luciferase complementation imaging assays confirmed that FtbHLH1 interacts with FtATG8a. This interaction depends on the AIM motifs (LEWYYL and QSWHFV) present in FtbHLH1, with both proteins co-localizing in the nucleus. The expression of FtbHLH1 was significantly induced by drought stress (P < 0.05), and its overexpression led to increased drought tolerance in transgenic Tartary buckwheat hairy roots. RNA sequencing revealed that FtbHLH1 up-regulated genes associated with stress response (e.g., FtCu/ZnSOD) as well as those involved in abscisic acid and methyl jasmonate biosynthesis and signaling pathways (e.g., FtCYP707As, FtRD29B, and FtJAZs). Further analysis indicated that the overexpression of FtbHLH1 enhances drought stress tolerance by altering the activities of antioxidant enzymes and promoting proline accumulation in both transgenic Arabidopsis and Tartary buckwheat hairy roots. This study provides theoretical support for selecting drought-resistant Tartary buckwheat varieties by elucidating the role of FtbHLH1 in the response to drought stress.