TheCsGPA1-CsAQPsmodule is essential for salt tolerance of cucumber seedlings

Key message CsGPA1 interacts with CsTIP1.1 (a member of CsAQPs) and suppression ofCsGPA1results the reverse expression ofCsAQPsin leaves and roots, resulting in declining water content of cucumber seedlings under salt stress. Salt stress seriously affects cucumber growth and development. Whether the G-protein alpha subunit functions in cucumber during salt stress and its regulation mechanism remains unknown. We interrogatedCsGPA1-RNAi lines to identify the role ofCsGPA1during salt stress. Phenotypically, compared with wild type, leaves were severely withered, and root cells showed signs of senescence under salt stress for RNAi lines. Compared with WT, SOD and CAT activity, soluble protein and proline contents all decreased in RNAi lines, while malondialdehyde and relative electrical conductivity increased. Through screening the yeast two-hybrid library and combined with yeast two-hybrid and GST pull-down, the interaction of CsGPA1 with CsTIP1.1 was found the first time in a plant. Then, the expression of aquaporin (AQP) family genes was detected. The expression ofCsAQPgenes in leaves and roots was primarily up-regulated in WT under salt stress. However, interference byCsGPA1resulted in enhanced expression ofCsAQPsexcept forCsTIP3.2 in leaves, but reduced expression of someCsAQPsin roots under salt stress. Furthermore, principal component analysis ofCsAQPexpression profiles and linear regression analysis betweenCsGPA1andCsAQPsrevealed thatCsGPA1reversely regulated the expression ofCsAQPsin leaves and roots under salt stress. Moreover, the water content in leaves and roots of RNAi seedlings significantly decreased compared with WT under salt stress. Overall, CsGPA1 interacts with CsTIP1.1 and suppression ofCsGPA1results in opposite patterns of expression ofCsAQPsin leaves and roots, resulting in declining water content of cucumber under salt stress.