CsAHL20 negatively regulates epi-catechins biosynthesis under drought stress in Camellia sinensis

Catechins are an integral part of the beneficial compound profile of the tea, and their biosynthesis critically responds to several biotic and abiotic factors. Drought is one of the important abiotic factors affecting their biosynthesis. The molecular mechanism of their biosynthesis during drought stress remains unclear. A transcription factor, AHL, strongly responds to drought stress, and its exploration in tea plants could unveil the drought-associated mechanism of catechin biosynthesis. The results of CsAHL gene family identification and drought transcriptome data of tea plants marked a transcription factor, CsAHL20, possessing an AT-hook motif and the nucleus as its locality. This transcription factor was significantly up-regulated under drought and had a significant negative correlation with epi-catechins content. After overexpression of CsAHL20, the epi-catechins' biosynthesis key gene, CsANR, was significantly down-regulated along with significantly reduced epi-catechin contents. On the contrary, after silencing CsAHL20, CsANR was up-regulated, and epi-catechin contents were increased significantly. The dual-luciferase reporter assay and electrophoretic mobility shift assay showed that CsAHL20 could bind to the promoter of CsANR and inhibit its transcription. This study revealed that CsAHL20 inhibited the transcription of CsANR, thereby negatively regulating the epi-catechins biosynthesis under drought, which laid a foundation for improving the quality of tea.