Arginine-Rich Motif-Tandem CCCH Zinc Finger BnaTZF1 Protein Enhances Drought Stress Tolerance by Post-transcriptional Regulation of Target mRNAs in Brassica napus

Drought stress severely threatens the productivity of Brassica napus. We revealed that two tandem CCCH zinc finger proteins, BnaTZF1A and BnaTZF1C, which are homologous to AtTZF1/2/3, function as crucial positive regulators of the drought response. Phenotypic, physiological, and cytological analyses revealed that overexpression of BnaTZF1A/1C improved the drought stress tolerance and led to late flowering, while knockdown of BnaTZF1A/1C dampened the drought tolerance. BnaTZF1A acts as an RNA-binding protein, binds to the 3'UTR stem-loop motifs of targets identified through RIP-seq and REMSA, including RALF and COP1-interactive protein, and is coregulated by BnaTZF1A and BnaTZF1C, resulting in depletion of target transcripts. BnaTZF1A also targeted BnaTZF1C mRNA and regulated its mRNA level to balance the stress signaling and fine-tune the drought stress response. Our results have unraveled the roles and possible regulatory mechanism of BnaTZF1 in response to drought stress, suggesting BnaTZF1A/1C as targets for improving drought stress tolerance in B. napus.