A zinc finger protein BBX19 interacts with ABF3 to affect drought tolerance negatively in chrysanthemum

Drought is an environmental factor that can severely influence plant development and distribution, and greatly affect the yield and economic value of crops. We characterizedCmBBX19, a BBX family subgroup IV member gene, from the transcriptome database ofChrysanthemum morifoliumin response to drought stress. Drought stress and ABA treatments downregulated the expression ofCmBBX19. We generatedCmBBX19-overexpressing (CmBBX19-OX) lines andCmBBX19-suppressing lines (CmBBX19-RNAi), and found that suppressed expression ofCmBBX19led to enhanced drought tolerance compared with the wild-type (WT) controls, whileCmBBX19-OX lines exhibited reduced drought tolerance. Downstream gene analysis showed thatCmBBX19modulates drought tolerance mainly through inducing changes in the expression of ABA-dependent pathway genes, including protective protein, redox balance and cell wall biogenesis genes, such asresponsive to ABA 18,peroxidase 12, andcellulose synthase-like protein G2. Moreover, CmBBX19 was shown to interact with CmABF3, a master ABA signaling component, to suppress expression of these downstream genes. We conclude that BBX19-ABF3 module functions in the regulation of drought tolerance of chrysanthemum through an ABA-dependent pathway.