GhNRPB3 Negatively Regulates Drought and Salt Tolerance in Cotton

RNA polymerase II (Pol II) has been shown to participate in various biological processes in plants, but its function in response to abiotic stress in cotton remains unclear. This study aimed to elucidate the role of the third-largest subunit of Pol II (NRBP3) in the response of cotton to drought and salt stress through molecular biology and physiological methods. qPCR was used to analyze the expression pattern of GhNRBP3 in roots, stems, leaves, and cotyledons and to detect changes in its expression under drought, NaCl, and ABA treatments. Using virus-induced gene silencing (VIGS) technology, GhNRBP3-silenced plants were obtained, and their physiological indicators under drought and salt stress, as well as the expression levels of the drought stress-related genes GhRD22 and GhRD26, were measured. This study revealed that GhNRBP3 is widely expressed in roots, stems, leaves, and cotyledons and that its expression is significantly induced by drought, NaCl, and ABA treatments. Compared to wild-type plants, the drought resistance, survival rate, and peroxidase activity of the GhNRPB3-silenced plants significantly increased, whereas the malondialdehyde content significantly decreased. Moreover, the expression levels of the drought-responsive genes GhRD22 and GhRD26 significantly increased. The salt tolerance of the GhNRPB3-silenced plants also increased, as reflected by decreased leaf wilting and significant increases in root growth parameters (including root length, root area, and root volume). These results indicate that GhNRBP3 plays a crucial role in mediating the adaptation of cotton to drought and salt stress by regulating the expression of stress-related genes.