A key bHLH transcription factor, CsbHLH18, negatively regulates catechin biosynthesis in response to water stress

Water stress, a common abiotic stress, greatly influences the growth and development of tea plants, and the biosynthesis and accumulation of connotation substances, ultimately affecting the tea’s final quality. To study the correlation between water stress and the biosynthesis of connotation substances in tea, firstly, water stress treatment was given to tea plants, and decreased catechins content was observed with increasing water stress duration. The expression of CsANR1, an important gene in the catechins synthesis pathway, decreased significantly, as verified by transcriptome data and RT-qPCR. WGCNA analysis of transcriptome data identified a bHLH gene that is highly negatively correlated with catechin content and CsANR1 expression, and named CsBhlh18 . CsBhlh18’s promoter analysis revealed that this gene can directly respond to water stress and indirectly respond to water stress by responding to abscisic acid. The transient overexpression of CsbHLH18 exhibited significantly decreased CsANR1 expression and ultimately catechins content in leaves. In contrast, silencing CsbHLH18 resulted in significantly increased CsANR1 expression and catechin content. Further experiments, including Y1H, dual luciferase analysis, and EMSA, demonstrated that CsBhlh18 has direct affinity with the CsANR1 promoter’s G-box sequence, negatively regulating its expression, and thereby inhibiting the biosynthesis and accumulation of catechins in tea plants. • Csbhlh18 , a key gene of the bHLH family, was found in water-stressed tea plants. • CsbHLH18 can also respond to abscisic acid, indirectly responding to water stress. • Csbhlh18 directly binds to the promoter of CsANR1 , thereby inhibiting its expression. • CsbHLH18 inhibits the CsANR1 expression, leading to decreased catechin content.