RsERF40contributes to cold stress tolerance and cell expansion of taproot in radish (Raphanus sativusL.)

The growth and development of taproots are inhibited by cold stress in radish (Raphanus sativusL.). Ethylene-responsive element binding factors (ERF) are key participators in the cold stress response and growth regulation of plants. However, the function of ERFgenes in cold tolerance and root development in radish remains elusive. Here, we showed that the secondary growth of radish taproots was inhibited by cold stress. Comparative transcriptome analysis demonstrated that the RsERF40gene is an important regulator of the cold stress response and root growth regulation. The cold tolerance of transgenic Arabidopsisplants overexpressing the RsERF40gene was significantly improved. Overexpressing RsERF40in the cold-sensitive radish genotype and silencing RsERF40in the cold-tolerant radish genotype indicated that RsERF40was beneficial for alleviating oxidative damage under cold stress in radish. Transgenic Arabidopsisseedlings showed an increase in the elongation and radial growth of dark-grown roots. RT-qPCR analysis showed that the expression of the cold-related genes (CORs) RsCOR78and RsCOR413PM1and the cell wall strengthening-related genes RsCESA6and RsEXPB3was upregulated in transgenic Arabidopsisseedlings. Yeast one-hybrid (Y1H) and dual-luciferase reporter assays (DLA) revealed that RsERF40 directly regulates RsCOR78, RsCOR413PM1, RsCESA6and RsEXPB3expression, illustrating that RsERF40 enhances cold tolerance and taproot growth by modulating osmotic adjustment and cell wall mechanical strength in radish. In this study, the RsERF40-regulon was firstly found to be a new cold response pathway independent of the CBF-COR pathway conferring cold stress tolerance with increasing radish taproot growth. These results provided novel insight into the molecular mechanism underlying cold stress response and would facilitate the genetic improvement of cold tolerance in radish and other root vegetable crops.