The BraBRI1-BraBZR1/BraBES1 module regulates proteoglycan- and brassinosteroid-induced thermotolerance in Pakchoi

As a globally cultivated leafy vegetable and an important economic crop, the production of Pakchoi (Brassica rapa ssp. chinensis var. communis) is increasingly threatened by high-temperature stress, often resulting in reduced yields and even complete loss. In this study, we systematically investigated the potential function of a proteoglycan, LEPS1, which was extracted from the spent substrate of Lentinula edodes, on regulating the thermotolerance of Pakchoi. We found that LEPS1 could significantly improve the thermotolerance of Pakchoi by modulating brassinosteroid (BR) signaling. Specifically, LEPS1 promotes BR biosynthesis and activates BR signal transduction; silencing of BR receptor BraBRI1 significantly downregulates LEPS1- and BR-induced thermotolerance in Pakchoi. We also found the core transcription factors BraBZR1 and BraBES1 directly binding to the promoters of heat-responsive gene and enhance their transcriptional activity, thereby improving the plant thermotolerance. Thus, our results revealed that the proteoglycan LEPS1 and BR enhances the thermotolerance of Pakchoi in a BraBRI1-BraBZR1/BraBES1 module dependent manner. These findings not only elucidated the molecular mechanisms through which the proteoglycan LEPS1 and BR induce thermotolerance, but also offer molecular targets and novel approaches to enhance the thermotolerance of Brassica crops.