SlbHLH086/SlbHLH096-SlXTH23 module regulates the drought tolerance of tomato by altering cell wall components and thickness

SlXTH23 is identified to negatively respond to tomato drought stress. SlbHLH086 and SlbHLH096 directly bind and regulate the expression of SlXTH23 . SlbHLH086 interacts with SlbHLH096 and antagonistically regulate the expression of SlXTH23. bHLH086/bHLH096- XTH23 alters cell wall components and thickness to regulate drought tolerance. Drought imposes a severe impediment to plant growth and development, cause yield and quality to decline. Xyloglucan endotransglucosylase/hydrolase (XTH) is a kind of cell wall-modifying protein, and contributes to cell wall assembly. However, whether XTHs are involved in the drought stress of tomato ( Solanum lycopersicum L.), and its mechanism and upstream regulatory factors remain unclear. Here, SlXTH23 is identified to negatively respond to drought stress in tomato. SlXTH23 knockout tomato plants increase the content of cellulose and hemicellulose, as well as the thickness of secondary cell wall in roots, and enhance drought tolerance. In contrast, SlXTH23 overexpressed transgenic tomato plants are sensitive to drought stress. Two basic helix-loop-helix transcription factors, SlbHLH086 and SlbHLH096, are identified to directly bind and regulate SlXTH23 . Silencing SlbHLH086 alone or in combination with SlbHLH096 enhances drought tolerance by stimulating the expression of SlXTH23 and promoting the thickness of secondary cell wall in tomato roots. Silencing SlbHLH096 renders plants sensitive to drought stress. In addition, SlbHLH086 interacts with SlbHLH096, and SlbHLH086 prevents the inhibitory effect of SlbHLH096 on the expression of SlXTH23 . In summary, this study revealed the molecular mechanism that SlbHLH086/SlbHLH096- SlXTH23 module regulates the drought tolerance of tomato by altering cell wall components and thickness, providing a novel mechanistic insight for breeding drought tolerant tomato cultivars.