SmHSFA8 Enhances the Heat Tolerance of Eggplant by Regulating the SmEGY3-SmCSD1 Module and Promoting SmF3H-mediated Flavonoid Biosynthesis.

High temperature (HT) is a major environmental factor that restrains eggplant growth and production. Heat shock factors (HSFs) play a vital role in the response of plants to high-temperature stress (HTS). However, the molecular mechanism by which HSFs regulate heat tolerance in eggplants remains unclear. Previously, we reported that SmEGY3 enhanced the heat tolerance of eggplant. Herein, SmHSFA8 activated SmEGY3 expression and interacted with SmEGY3 protein to enhance the activation function of SmEGY3 on SmCSD1. Virus-induced gene silencing (VIGS) and overexpression assays suggested that SmHSFA8 positively regulated heat tolerance in plants. SmHSFA8 enhanced the heat tolerance of tomato plants by promoting SlEGY3 expression, HO production and HO-mediated retrograde signalling pathway. DNA affinity purification sequencing (DAP-seq) analysis revealed that SmHSPs (SmHSP70, SmHSP70B and SmHSP21) and SmF3H were candidate downstream target genes of SmHSFA8. SmHSFA8 regulated the expression of HSPs and F3H and flavonoid content in plants. The silencing of SmF3H by VIGS reduced the flavonoid content and heat tolerance of eggplant. In addition, exogenous flavonoid treatment alleviated the HTS damage to eggplants. These results indicated that SmHSFA8 enhanced the heat tolerance of eggplant by activating SmHSPs exprerssion, mediating the SmEGY3-SmCSD1 module, and promoting SmF3H-mediated flavonoid biosynthesis.