Drought shortens cotton fiber length by inhibiting biosynthesis, remodeling and loosening of the primary cell wall

Drought could severely impair the formation of cotton fiber length, yet the underlying mechanism is not fully understood. Here, the effects of drought on cotton fiber elongation processes including primary cell wall biosynthesis, remodeling and loosening and osmolyte accumulation were investigated from transcriptomic and physiological levels by using two upland cotton cultivars (Dexiamian 1 and Yuzaomian 9110). The results showed that the cotton fiber elongation was significantly stunted under drought, and the biggest reduction in fiber length appeared at 10 days post anthesis. The total osmolytes concentration of cotton fiber sap was increased by drought via promoting the accumulation of malate and K+, which was favorable to fiber elongation. Whilst the biosynthesis of fiber primary cell wall components including pectin, hemicellulose and cellulose was inhibited under drought by suppressing the expression of galacturonosyltransferase (GhGAUT) and galacturonosyltransferase-like (GhGATL), xylosyltransferase (GhXXT), and cellulose synthase (GhCesA) respectively, leading to reduced fiber cell wall biomass. Meanwhile, drought restricted the remodeling and loosening of fiber primary cell wall by suppressing the expression of genes related to primary cell wall decomposition including pectin methylesterase (GhPME), xyloglucan endotransglucosylase/hydrolase (GhXTH), and endoglucanase (GhEG), and alpha-expansin (GhEXPA). Taken together, it is concluded that the shortened fiber length induced by drought was caused by restricted primary fiber cell wall biosynthesis, remodeling, and loosening but not the lowered osmotic potential. Overall, our work provides new insights into understanding the mechanisms by which drought shortens cotton fiber length.