GATA3‐COMT1‐Melatonin as Upstream Signaling of ABA Participated in Se‐Enhanced Cold Tolerance by Regulate Iron Uptake and Distribution in <i>Cucumis sativus</i> L

Selenium has the function of bio-stimulating hormone. However, the underlying physiological and molecular mechanisms of melatonin and abscisic acid as secondary messengers in improving cold tolerance by selenium are limited. This study investigated the effects of selenite on the cold stress of cucumber seedlings. The results showed that the content of endogenesis abscisic acid significantly changed with exogenous application of selenite under cold stress. Interestingly, we found that the content of iron significantly changed in this process. Iron uptake and distribution may be the important reason of selenium alleviates cold injury of cucumber seedlings. Whole genes transcriptome was used for screening key genes on leaf and root of cucumber seedlings. To determine the interrelation between abscisic acid and melatonin in selenite alleviating cold stress, abscisic acid inhibitor fluridone and melatonin synthesis inhibitor p-chlorophenylalanine were used for in-depth study. The results indicate that melatonin as upstream signal of ABA involved in selenium enhanced cucumber cold tolerance. The results of yeast single hybridization, EMSA, LUC, and overexpression transgenic showed that the transcription factor CsGATA3 regulates the expression of CsCOMT1 in vitro and in vivo and affects melatonin content. This study provides a theoretical basis for cucumber cultivation and breeding.