Due to a labor shortage, the mechanical harvesting of tea plantations has become a focal point. However, mechanical harvest efficiency was hampered by droopy leaves, leading to a high rate of broken tea shoots and leaves. Here, we dissected the genetic structure of leaf droopiness in tea plants using genome-wide association studies (GWAS) on 146 accessions, combined with transcriptome from 2 accessions with contrasting droopy leaf phenotypes. A set of 16 quantitative trait loci (QTLs) containing 54 SNPs and 34 corresponding candidate genes associated with droopiness were then identified. Among these, CsEXL3 (EXORDIUM-LIKE 3) from Chromosome 1 emerged as a candidate gene. Further investigations revealed that silencing CsEXL3 in tea plants resulted in weaker vascular cell malformation and brassinosteroid-induced leaf droopiness. Additionally, brassinosteroid signal factor CsBES1.2 was proved to participate in CsEXL3-induced droopiness and vascular cell malformation via using the CsBES1.2-silencing tea plant. Notably, CsBES1.2 bound on the E-box of CsEXL3 promoter to transcriptionally activate CsEXL3 expression as CUT&TAG based ChIP-qPCR and ChIP-seq suggested in vivo and EMSA and Y1H indicated in vitro. Furthermore, CsEXL3 instead of CsBES1.2 decreased lignin content and the expressing levels of lignin biosynthesis genes. Overall, our findings suggest that CsEXL3 regulates droopy leaves, partially through the transcriptional activation of CsBES1.2, with the potential to improve mechanical harvest efficiency in tea plantations.

中文翻译：

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CsEXL3在CsBES1.2转录激活下调节茶树机械收获相关的下垂叶片

由于劳动力短缺，茶园机械采收成为焦点。然而，机械采收效率因叶片下垂而受到影响，导致茶芽和茶叶的破碎率很高。在这里，我们利用 146 个种质的全基因组关联研究 (GWAS)，结合 2 个具有对比下垂叶表型的种质的转录组，剖析了茶树叶片下垂的遗传结构。然后鉴定出一组 16 个数量性状基因座 (QTL)，其中包含 54 个 SNP 和 34 个与下垂相关的相应候选基因。其中，来自1号染色体的CsEXL3（EXORDIUM-LIKE 3）成为候选基因。进一步的研究表明，沉默茶树中的 CsEXL3 会导致较弱的维管细胞畸形和油菜素类固醇引起的叶子下垂。此外，通过使用CsBES1.2沉默茶树，油菜素类固醇信号因子CsBES1.2被证明参与CsEXL3诱导的下垂和血管细胞畸形。值得注意的是，CsBES1.2 结合在 CsEXL3 启动子的 E-box 上，以转录方式激活 CsEXL3 表达，如体内基于 CUT&TAG 的 ChIP-qPCR 和 ChIP-seq 以及体外 EMSA 和 Y1H 所示。此外，CsEXL3代替CsBES1.2降低了木质素含量和木质素生物合成基因的表达水平。总的来说，我们的研究结果表明，CsEXL3 部分通过 CsBES1.2 的转录激活来调节下垂的叶子，有可能提高茶园的机械收获效率。