CsSAD1-silenced in tea leaves impairs drought tolerance by decreasing plasma membrane H+-ATPase activity

Drought stress is a negative regulatory factor that leads to reduced yield and quality. Unsaturated fatty acids controlled by stearic acid desaturase play a key role in mediating membrane fluidity to cope with drought stress; however, the response of CsSAD1 to drought stress is poorly understood. In this study, CsSAD1-silenced leaves displayed weakened drought tolerance, accompanied by lower Fv/Fm and higher Malondialdehyde (MDA) levels. However, CsSAD1-overexpressing Arabidopsis exhibited an elevated tolerance to drought stress in pot experiments. Furthermore, CsSAD1-silenced leaves displayed reduced plasma membrane H+-ATPase activity, which promoted membrane potential depolarization and led to a massive K+ loss under Polyethylene glycol (PEG) stress. In contrast, CsSAD1-overexpressing Arabidopsis showed higher plasma membrane H+-ATPase activity and alleviated membrane potential depolarization, which in turn mitigated K+ loss under drought stress. Moreover, an exogenous supply of Na3VO4 (P-type ATPases inhibitor) further indicated that the difference in K+ efflux in the transgenic plants was dependent on the plasma membrane H+-ATPase. Therefore, silencing CsSAD1 in tea leaves inhibited plasma membrane H+-ATPase activity, which was the primary factor contributing to the maintenance of K+ homeostasis and, consequently, drought tolerance in tea plants.