Vapor pressure deficit (VPD), defined as the difference between the actual water vapor pressure and the saturation vapor pressure in the air, is a core indicator of atmospheric aridity.  High VPD induces intensified water loss via plant transpiration, thereby constraining water uptake and photosynthetic capacity.  The dynamic functions and molecular regulatory mechanisms of plasma membrane intrinsic proteins (PIPs), key aquaporins mediating rapid transmembrane water transport, remain unclear during plant responses to high VPD stress.  In this study, we elucidated the regulatory role of SlPIP1;7 in regulating the multi-level adaptation strategy of tomato (Solanum lycopersicum) at the morphological, physiological, and molecular levels under high VPD conditions.  The results indicate that, compared to wild-type (WT) plants, SlPIP1;7 overexpressing (OE) plants exhibit superior growth performance under high VPD conditions.  The overexpression of SlPIP1;7 significantly enhances the reactive oxygen species (ROS) scavenging efficiency, effectively protecting plant cells from oxidative damage.  This protective mechanism for maintaining ROS homeostasis is closely associated with stomatal function.  The overexpression of SlPIP1;7 can regulate stomatal morphology, size, and aperture dynamics, thereby promoting efficient utilization of water and carbon dioxide and enhancing the overall physiological regulatory capacity of plants under stress conditions.  Additionally, we identified the ethylene response factor SlERF4 as an upstream regulatory factor in this adaptive network.  Yeast one-hybrid (Y1H) and dual-luciferase (LUC) assays demonstrate that the transcription factor SlERF4 can bind to the SlPIP1;7 promoter, enhancing its expression and functionality.  This interaction further underscores the pivotal role of SlPIP1;7 in combating high VPD stress.  In summary, our study elucidates the crucial function of SlPIP1;7 in plant response and acclimation to high VPD stress.  These findings expand our understanding of the molecular mechanisms underlying plant acclimation to environmental stresses and provide a reference for future breeding strategies aimed at developing drought-resistant crops.

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.