The study reveals that drought stress increases the expression of CsMPK4a, a mitogen-activated protein kinase, in tea leaves. CsMPK4a interacts with the WD40-repeat protein CsWD40, phosphorylating it at specific sites (Ser-216, Thr-221, and Ser-253). This phosphorylation disrupts CsWD40's interaction with key transcription factors responsible for flavonoid biosynthesis, leading to reduced flavonoid production.
Experiments introducing dephosphorylated (CsWD403A) and phosphorylated (CsWD403D) variants of CsWD40 into Arabidopsis plants further confirmed this regulatory mechanism. Dephosphorylated CsWD40 enhanced flavonoid production, while phosphorylated CsWD40 significantly decreased it.
Additionally, transient overexpression of these variants in tea leaves under stress conditions mirrored these results, indicating the phosphorylation state of CsWD40 plays a crucial role in modulating flavonoid biosynthesis. This detailed analysis provides new insights into how tea plants respond to drought at the molecular level, highlighting potential targets for improving stress tolerance.
Dr. Liping Gao, one of the corresponding authors, stated, "Our findings uncover a critical regulatory mechanism that affects flavonoid biosynthesis in tea plants under drought stress. Understanding this pathway opens up new possibilities for breeding drought-resistant tea varieties with optimized flavonoid content."
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