Aquaporin CmPIP2;3 links H2O2 signal and antioxidation to modulate trehalose-induced cold tolerance in melon seedlings

Cold stress severely restricts the growth and development of cold-sensitive crops. Trehalose (Tre), known as the "sugar of life", plays key roles in regulating plant cold tolerance by triggering antioxidation. However, the relevant regulatory mechanism remains unclear. Here, we confirmed that Tre triggers apoplastic hydrogen peroxide (H2O2) production and thus plays key roles in improving the cold tolerance of melon (Cucumis melo var. makuwa Makino) seedlings. Moreover, Tre treatment can promote the transport of apoplastic H2O2 to the cytoplasm. This physiological process may depend on aquaporins. Further studies showed that a Tre-responsive plasma membrane intrinsic protein 2;3 (CmPIP2;3) had strong H2O2 transport function and that silencing CmPIP2;3 significantly weakened apoplastic H2O2 transport and reduced the cold tolerance of melon seedlings. Yeast library and protein-DNA interaction technology were then used to screen 2 Tre-responsive transcription factors, abscisic acid-responsive element (ABRE)-binding factor 2 (CmABF2) and ABRE-binding factor 3 (CmABF3), which can bind to the ABRE motif of the CmPIP2;3 promoter and activate its expression. Silencing of CmABF2 and CmABF3 further dramatically increased the ratio of apoplastic H2O2/cytoplasm H2O2 and reduced the cold tolerance of melon seedlings. This study uncovered that Tre treatment induces CmABF2/3 to positively regulate CmPIP2;3 expression. CmPIP2;3 subsequently enhances the cold tolerance of melon seedlings by promoting the transport of apoplastic H2O2 into the cytoplasm for conducting redox signals and stimulating downstream antioxidation.