AtDIV2, an R-R-type MYB transcription factor of Arabidopsis, negatively regulates salt stress by modulating ABA signaling.

KEY MESSAGE: AtDIV2 integrates ABA signaling to negatively regulate salt stress in Arabidopsis. AmDIV (DIVARICATA) is a functional MYB transcription factor (TF) that regulates ventral identity during floral development in Antirrhinum. There are six members of DIV homologs in Arabidopsis; however, the functions of these proteins are largely unknown. Here, we characterized an R-R-type MYB TF AtDIV2, which is involved in salt stress responses and abscisic acid (ABA) signaling. Although universally expressed in tissues, the nuclear-localized AtDIV2 appeared not to be involved in seedling development processes. However, upon exposure to salt stress and exogenous ABA, the transcripts of AtDIV2 are markedly increased in wild-type (Wt) plants. The loss-of-function mutant div2 displayed much more tolerance to salt stress, and several salt-responsive genes were up-regulated. In addition, the div2 mutant showed higher sensitivity to ABA during seed germination. And the germination variance between the Wt and div2 mutant cannot be rectified by treatment with both ABA and sodium tungstate at the same time. ELISA results showed that the endogenous ABA content in the div2 mutant is clearly increased than that in Wt plants. Furthermore, the transcriptional expressions of several ABA-related genes, including ABA1 and ABI3, were elevated. Taken together, our results suggest that the R-R-type MYB TF AtDIV2 plays negative roles in salt stress and is required for ABA signaling in Arabidopsis.