SlMYB41 induced by exogenous brassinosteroids negatively regulates the cold resistance of tomato

Abstract

Abstract Brassinosteroids regulate plant development and response to stress. This study demonstrated that exogenous brassinosteroid application can increase plant cold-stress tolerance. However, the effects of exogenous brassinosteroids on the cold resistance of tomatoes require further investigation. Our results indicated that exogenous 24-epibrassinolide application increased brassinosteroid content and cold resistance in tomato (Solanum lycopersicum cv. Micro-Tom) plants. RNA-seq results showed that the expression of most genes encoding proteins in photosystems I and II and photosynthetic characteristics were downregulated and that the degree of downregulation in brassinosteroid-treated plants was weaker than that in untreated (MT) plants. Furthermore, the net photosynthetic rate and maximum photochemical efficiency of brassinosteroid-treated plants were significantly higher than those of MT plants under chilling stress. Chilling stress also regulated the expression levels of 60 transcription factors. The expression of 34 genes was downregulated, and 26 were upregulated. The degree of regulation in the brassinosteroid-treated plants was lower than in the MT plants. RNA-seq results showed that brassinosteroids induced SlMYB41 expression and rapidly so during cold stress. In addition, the degree of wilting was more severe in SlMYB41 overexpression plants than in MT plants under chilling stress. Additionally, the relative electrolyte leakage and malondialdehyde content in SlMYB41OE plants were significantly higher than in MT plants. The contents of O2− and H2O2 in MT plants were significantly lower than those in SlMYB41OE plants after chilling stress. The activities of SOD, POD and CAT were significant higher in MT plants than in SlMYB41OE plants. Expression levels of four cold-responsive genes were significantly lower in SlMYB41OE plants than in MT plants after chilling stress. These results indicated that SlMYB41 overexpression reduced chilling tolerance. Therefore, the increase of plant cold resistance by application brassinosteroid is not achieved through SlMYB41.