Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot in crucifers, produces a membrane‐bound yellow pigment called xanthomonadin to protect against photobiological and peroxidative damage, and uses a quorum‐sensing mechanism mediated by the diffusible signal factor (DSF) family signals to regulate virulence factors production. The Xcc gene XCC4003, annotated as Xcc fabG3, is located in the pig cluster, which may be responsible for xanthomonadin synthesis. We report that fabG3 expression restored the growth of the Escherichia coli fabG temperature‐sensitive mutant CL104 under non‐permissive conditions. In vitro assays demonstrated that FabG3 catalyses the reduction of 3‐oxoacyl‐acyl carrier protein (ACP) intermediates in fatty acid synthetic reactions, although FabG3 had a lower activity than FabG1. Moreover, the fabG3 deletion did not affect growth or fatty acid composition. These results indicate that Xcc fabG3 encodes a 3‐oxoacyl‐ACP reductase, but is not essential for growth or fatty acid synthesis. However, the Xcc fabG3 knock‐out mutant abolished xanthomonadin production, which could be only restored by wild‐type fabG3, but not by other 3‐oxoacyl‐ACP reductase‐encoding genes, indicating that Xcc FabG3 is specifically involved in xanthomonadin biosynthesis. Additionally, our study also shows that the Xcc fabG3‐disrupted mutant affects Xcc virulence in host plants.

中文翻译：

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一种新型的3-氧代酰基-ACP还原酶（FabG3）参与了油菜黄单胞菌pv的黄单孢菌素生物合成。桔梗。

Xanthomonas campestris pv。campestris（Xcc）是十字花科植物中黑腐病的病原体，可产生一种称为黄嘌呤酮的膜结合黄色色素，可防止光生物和过氧化损伤，并使用由可扩散信号因子（DSF）家族信号介导的群体感应机制调节毒力因子的产生。所述XCC基因XCC4003，注释为XCC fabG3，位于在猪簇，其可以是负责xanthomonadin合成。我们报告fabG3的表达恢复了非允许条件下大肠杆菌fabG温度敏感突变体CL104的生长。体外分析表明，尽管FabG3的活性比FabG1低，但FabG3可以催化脂肪酸合成反应中3-氧羰基酰基载体蛋白（ACP）中间体的还原。此外，fabG3缺失不影响生长或脂肪酸组成。这些结果表明，Xcc fabG3编码3-氧代酰基-ACP还原酶，但对于生长或脂肪酸合成不是必需的。然而，XCC fabG3敲除突变体废除xanthomonadin生产，这可以通过野生型只恢复fabG3，而不是由其它3-氧代酰基-ACP还原酶编码基因，表明XCC FabG3具体涉及xanthomonadin生物合成。此外，我们的研究还表明XCC fabG3 -disrupted突变影响XCC毒力在寄主植物。