High air humidity enhances catechin accumulation in tea plants (Camellia sinensis L.) through a specific molecular pathway

Catechins are key components influencing the flavor and health benefits of tea. While environmental effects on catechin biosynthesis are widely studied, how air humidity regulates this process remains unclear. In this study, tea cuttings were cultivated in growth chambers under controlled humidity conditions, and their responses in catechin biosynthesis were investigated using HPLC, qPCR, and bioinformatics analyses. The results showed that 90% air humidity treatment significantly increased esterified catechin contents, including epigallocatechin gallate, epicatechin gallate, gallocatechin gallate. Moreover, high air humidity upregulated the expression of structural genes and transcription factors including CsCHS, CsC4H, CsANS, CsLAR1, CsDFR, CsANR2 and CsTCP , in contrast to the downregulation of microRNAs (miR529, miR3444b, miR2868, miR169a). Bioinformatics analysis combined with antisense oligodeoxynucleotide (asODN) confirmed the regulatory role of CsTCP22 on CsC4H/CsLAR1 in tea plants. Collectively, the study reveals that high air humidity promotes catechin biosynthesis through specific regulatory pathway, providing a reference for optimizing air humidity management in tea plantations to enhance tea quality. • High air humidity increases the catechins content in tea plants, including EGCG, GCG, ECG, total esterified catechins, and total catechins. • Esterified catechins and non-esterified catechins exhibit opposite response patterns to air relative humidity; • The miR396d- CsTCP22 - CsC4H/CsLAR1 module mediates the response of catechin biosynthesis to changes in air humidity.