Alternative Splicing of CsCPL Relieves the Inhibitory Effect of CsCPL on Trichome Formation and Anthocyanin Biosynthesis in Tea Plants

The downy buds on tender branches of tea plants are used to produce high-quality green, black, dark, and white teas due to their abundance of polyphenols, theanine, caffeine, and aroma constituents. The trichomes covering the downy buds (known as 'háo' in Chinese) contribute significantly to beverage quality. However, the molecular and regulatory mechanisms underlying tea trichome development are still not fully elucidated. Here, we identify an R3 MYB transcription repressor involved in trichome formation, CsCAPRIC-like (CPL), which undergoes alternative splicing in tea plants to generate two transcripts: the conventional isoform CsCPL and the intron-retaining form CsCPL AS. The conventional isoform CsCPL competitively binds to CsGL3 (a bHLH component of the MYB‑bHLH‑WD40 complex), thereby preventing the formation of the CsMYB15-CsGL3-CsWD40 and CsMYB6-CsGL3-CsWD40 complexes, and further inhibiting the expression of two key downstream genes: CsGL2 (GLABRA2, HD-Zip IV transcription factor), responsible for trichome formation, and CsANS (anthocyanidin synthase), responsible for anthocyanin biosynthesis. Due to alternative splicing within the conserved CsGL3-binding motif, the CsCPL AS cannot bind to CsGL3, but can interact with the conventional isoform CsCPL to form a non-functional heterodimer. This interaction alleviates the inhibitory effect of CsCPL protein on the formation of MBW complexes, thereby reducing its inhibitory effect on trichome formation and anthocyanin biosynthesis. These findings reveal a unique mechanism for trichome formation mediated by alternative splicing of CsCPL, which is fundamental to tea plant growth and quality.