Root Cortical Senescence Enhances Drought Tolerance in Cotton

The root cortical senescence (RCS) is closely associated with root absorptive function. However, characteristics and responses of RCS to drought stress in cotton have received little attention. This study subjected the drought-tolerant variety 'Guoxin 02' and the drought-sensitive variety 'Ji 228' to drought stress (8% PEG6000) and no-stress (0% PEG6000) treatments to determine the characteristics and responses of cotton RCS to drought stress. The results showed that the greater the distance from the root tip, the more severe the RCS occurrence under drought stress compared with non-stress treatment. The occurrence of RCS in 'Guoxin 02' increased by 14.03%-20.18% compared to 'Ji 228' under drought stress. The RCS was negatively correlated with root respiration but positively correlated with root length and leaf water potential. The silencing of RCS-related genes (GhSAG12 and GhbHLH121) can mitigate the drought-induced RCS phenomenon in cotton; however, reduced drought tolerance. Exogenous abscisic acid (ABA) treatment can promote RCS generation. Conversely, ABA synthesis exhibits contrasting effects. In summary, endogenous hormones regulated RCS, which reduced the root metabolic and seemingly achieved more resource redistribution to new roots, thereby fully utilize deep water resources. Thus, the study demonstrates the potential of RCS in improving the drought stress tolerance of cotton.