Transcription factor CsNAC25 mediating dual roles in tea plant secondary cell wall formation and trichome development

Trichomes are a key feature of tea plants (Camellia sinensis L.) and essential for tea flavor compound formation, but their developmental mechanisms are still unclear. This study identified a transcription factor, CsNAC25, which positively regulates trichome formation in the 'Qiancha 1' tea plant cultivar. Phylogenetic analysis showed that CsNAC25 shares the highest homology with Arabidopsis XND1, and in situ hybridization revealed its specific expression in xylem cells and in trichomes of tea plant. Overexpression of CsNAC25 significantly inhibited xylem cell differentiation, reduced lignin and cellulose content, and led to a marked increase in trichome density. Conversely, using virus-induced gene silencing to silence CsNAC25 in tea plants resulted in reduced trichome density and elevated lignin content. Quantitative real-time PCR analysis showed that the expression of key phenylpropanoid pathway genes, such as NtPAL2, Nt4CL1, NtCAD1, and NtCCR1, was significantly reduced in the overexpression lines. Conversely, in the CsNAC25-silenced tea cuttings, the expression of CsPAL1, Cs4CL2, CsCAD1, and CsCCR1 was drastically increased. Moreover, the expression of CsMYB1, a positive regulator of trichome development, was significantly decreased in the CsNAC25-silenced lines. Further yeast one-hybrid and dual luciferase assays showed that CsNAC25 binds to the CsCCR1 promoter and represses its expression, suggesting that CsNAC25 regulates trichome development possibly by modulating CsCCR1 and impacting resource allocation within the phenylpropanoid metabolic network. In summary, our findings indicate that CsNAC25 in tea plants plays a dual role in regulating the secondary cell wall formation and trichome development.