<scp>CsWRKY75</scp> ‐ <scp>CsABF4</scp> module regulated beta‐amylases‐mediated starch degradation to enhance drought resistance in tea plants ( <i>Camellia sinensis</i> )

Drought, one of the major abiotic stresses, profoundly limits the growth, yield, and quality formation of tea plants. Here, we revealed that β-amylases (BAM)-mediated starch degradation and their transcriptional regulators play an important role in drought resistance of tea plants. Drought stress significantly induced the expression of CsBAM1a, CsBAM1b, CsBAM3, and CsBAM9, followed by starch degradation and accumulation of soluble sugars as osmoprotectants for enhancement of drought tolerance in tea plants. Recombinant CsBAM1a protein showed strong starch-degrading activity, whereas silencing CsBAM1a in tea plants substantially suppressed starch degradation. CsABF4 directly bound to the ABA-responsive elements in the promoters of CsBAM1a, CsBAM1b, CsBAM3, and CsBAM9, activating their transcription and promoting starch degradation in tea plants. Overexpression of CsBAM1a and CsABF4 significantly enhanced the drought resistance of transgenic Arabidopsis plants. In addition, CsWRKY75 also directly bound to CsBAM1a, CsBAM1b, and CsBAM9 promoters and activated their transcription. Alternatively, CsWRKY75 participated in the CsABF4 regulation of four CsBAM genes transactivation by directly activating CsABF4. These findings provide new insights into the regulation of drought stress responses and suggest potential strategies for improving drought resistance by modulating starch remobilization in tea plants.