Auxin promotes cucumber resistance to high ambient temperature by enhancing photosystem and activating DNA repair pathways

Global warming poses a huge challenge for plants to withstand increasing ambient temperatures. Cucumber is a kind of worldwide vegetable crop which is very sensitive to high temperature (HT). The mechanism of auxin affecting plant resistance to high temperature is still unclear. This study showed the relationship between auxin and heat resistance of cucumber. Here, we found that exogenous auxin improved cucumber heat tolerance by promoting root activity and mitigating the accumulation of ROS at the cotyledon stage. Additionally, exogenous auxin delayed internode shortening and leaf senescence under HT at three true-leaf stage. Exogenous auxin maintains photosystem Ⅱ (PS Ⅱ) stability in the thermotolerant cucumber plants. Transcriptome results indicated that photosynthesis and DNA repair processes were activated by exogenous 2,4-dichlorophenoxyacetic acid (2,4-D). Moreover, glutathione metabolism and carotenoid biosynthesis process were involved in ROS scavenging after the 2,4-D treatment under HT. In addition, overexpression of auxin biosynthesis gene CsYUC10b elevated cucumber resistance to high temperatures and enhanced the photosystem activity and DNA repair ability. Thus, auxin promoted heat resistance in cucumber by enhancing PS Ⅱ and activating DNA repair pathways.