CmSCL4 and CmR1MYB1 synergistically enhance the drought tolerance by regulation of ABA signaling in chrysanthemum

With water shortage worldwide, seeking drought resistance genes are of great value for molecular breeding. Here, we isolated a homologous AtSCL4/7 subfamily gene of GRAS transcription factor family from chrysanthemum and designated it as CmSCL4. CmSCL4 was responded to 20% PEG6000 treatment and its heterologous expression improved drought tolerance by up-regulating ABA signaling genes AtABI3 and AtABI4 in Arabidopsis. Moreover, the cotyledon greening rate, early seedling development and stomatal aperture of transgenic Arabidopsis are hypersensitivity to external ABA treatment. Meanwhile, overexpression and chimeric repression of CmSCL4 in chrysanthemum also conferred the increased or decreased drought tolerance and corresponding changes of the expression of CmABI4. Yeast two-hybrid screening of the cDNA library of chrysanthemum by CmSCL4 identified a MYB transcription factor as an important candidate partner, which was named as CmR1MYB1 hereafter. The interaction between CmSCL4 and CmR1MYB1 was further verified by in vitro pull-down, in vivo BiFC and Co-IP assays. CmR1MYB1 and CmSCL4 had similar expression patterns under 20% PEG6000 treatment. Heterologous expression of CmR1MYB1 in Arabidopsis also facilitated the expression levels of AtABI3 and AtABI4, resulted in the improved drought tolerance. These results demonstrated that CmSCL4 cooperates with CmR1MYB1 to modulate the dehydration tolerance of chrysanthemum, at least partially through the regulation of ABA-responsive genes.