Skin color is one of the major traits of fruit appearance quality in pear (Pyrus), which affects the fruit commodity value. Russet skin protects pear fruits from environmental stresses and its formation process is closely linked to lignin accumulation. However, the molecular regulatory networks underlying russet skin formation in pear fruits involve complex secondary metabolic pathways and remain elusive. Here, we explored the regulatory mechanisms underlying lignin accumulation in pear skin based on transcriptome sequencing, co-expression network analysis, and gene expression profiling. We identified a WRKY transcription factor gene, PbWRKY24, that regulates russet skin formation in pear fruits. The relative expression of PbWRKY24 in russet pear skin was significantly correlated with lignin content. We then verified the function of PbWRKY24 in lignin accumulation via genetic transformation. DNA affinity purification sequencing revealed that PbWRKY24 directly binds to the promoter of a lignin biosynthesis gene, PbPRX4. This binding was confirmed by yeast one-hybrid, dual-luciferase, and electrophoretic mobility shift assays. Overexpression of PbPRX4 in pear skin stimulated lignin accumulation and consequently promoted russet skin formation. This study provides a glimpse into the intricate lignin biosynthesis mechanisms during russet skin formation in pear fruits, which is of practical significance to pear breeding for fruit quality.

中文翻译：

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转录因子 PbWRKY24 通过调节木质素积累促进梨果实赤褐色表皮的形成


皮色是梨 （Pyrus） 果实外观品质的主要特征之一，影响水果商品价值。赤褐色的果皮保护梨果实免受环境压力，其形成过程与木质素积累密切相关。然而，梨果实中赤褐色表皮形成的分子调控网络涉及复杂的次生代谢途径，仍然难以捉摸。在这里，我们基于转录组测序、共表达网络分析和基因表达谱探讨了梨皮木质素积累的调控机制。我们鉴定了一个 WRKY 转录因子基因 PbWRKY24，它调节梨果实赤褐色表皮的形成。PbWRKY24 在赤褐色梨皮中的相对表达量与木质素含量显著相关。然后，我们通过遗传转化验证了 PbWRKY24 在木质素积累中的功能。DNA 亲和纯化测序显示，PbWRKY24 直接与木质素生物合成基因 PbPRX4 的启动子结合。这种结合通过酵母单杂交、双荧光素酶和电泳迁移率变化测定得到证实。梨皮中 PbPRX4 的过表达刺激了木质素积累，从而促进了赤褐色皮肤的形成。本研究揭示了梨果实赤褐色表皮形成过程中错综复杂的木质素生物合成机制，对梨果实品质育种具有现实意义。