Pan-genome Identification of CsYABBYs and Validation of Drought Stress Responses in Tea Plants

The YABBY family of transcription factors plays an important role in plant growth, development, and stress tolerance. To further explore how CsYABBY family members participate in the drought response mechanism in tea plants (Camellia sinensis L. O. Kuntze), we performed a family analysis based on the published pan-genomes of 22 tea varieties and identified a total of 27 CsYABBYs, including 4 near-core genes. Collinearity analysis and Ka/Ks results showed that four near-core genes, CsYABBY7, CsYABBY9, CsYABBY10, and CsYABBY11, were relatively conserved and under purifying selection during tea domestication. In addition, expression patterns showed their differential responses to drought stress. Functional experiments further confirmed that overexpression of CsYABBY7/10/11 could reduce the accumulation of reactive oxygen species and increase the activities of osmoregulatory substances and antioxidant enzymes, thereby enhancing drought resistance. Inhibition of these genes has the opposite effect. CsYABBY9 exhibits dosage-sensitive regulation, in which both overexpression and knockdown compromise drought tolerance.