Cho Yongmin, Rhyu Haerim, Lee Suhyun, Kim Dohyun, Kim Dae Sung, Lee Jisun H J, Han Sang-Wook
Department of Plant Science and Technology, Chung-Ang University, Anseong 17546, Korea.
State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan 430062, China.
Plant Pathol J. 2025 Jun;41(3):341-351. doi: 10.5423/PPJ.OA.03.2025.0036. Epub 2025 Jun 1.
Acidovorax citrulli (Ac) is a Gram-negative phytopathogenic bacterium causing bacterial fruit blotch (BFB) on cucurbit crops, specifically in the watermelon industry. However, cultivars of watermelon that are resistant to Ac have not been identified. Therefore, virulence factors/mechanisms in Ac must be characterized to develop alternative control strategies. Functions of a histidinol dehydrogenase, which is an essential enzyme for histidine biosynthesis, remain elusive in Ac. This study aims to elucidate the roles of histidinol dehydrogenase in Ac (HisDAc) using phenotype assays and proteomic analysis. The virulence of a mutant lacking a histidinol dehydrogenase, hisDAc:Tn5(EV), was diminished in geminated-seed inoculation and leaf infiltration assays, and the bacterium was impossible to grow without histidine in minimal media. However, treatment with exogenous histidine completely restored the virulence of the mutant on watermelon and its growth in minimal media, demonstrating that HisDAc is required for histidine biosynthesis, which contributes to virulence and growth. The comparative proteomic analysis indicates that HisDAc is involved in not only amino acid metabolism but also other biological mechanisms, including cell wall/membrane/envelope functions. This suggests that HisDAc may have pleiotropic effects. It was also confirmed that when Escherichia coli was incubated with Ac strains in water, the population level of E. coli increased in the presence of the mutant but not in the presence of the wild-type. This study leads to new insights regarding enzymes related to the production of primary metabolites and provides a promising target to discover an anti-virulence reagent to control BFB.
西瓜嗜酸菌（Ac）是一种革兰氏阴性植物病原菌，可导致葫芦科作物发生细菌性果斑病（BFB），尤其是在西瓜产业中。然而，尚未鉴定出对Ac具有抗性的西瓜品种。因此，必须对Ac中的毒力因子/机制进行表征，以制定替代控制策略。组氨醇脱氢酶是组氨酸生物合成所必需的一种酶，其在Ac中的功能仍不清楚。本研究旨在通过表型分析和蛋白质组学分析阐明组氨醇脱氢酶在Ac（HisDAc）中的作用。在发芽种子接种和叶片浸润试验中，缺乏组氨醇脱氢酶的突变体hisDAc:Tn5(EV)的毒力减弱，并且该细菌在基本培养基中没有组氨酸时无法生长。然而，用外源组氨酸处理可完全恢复该突变体在西瓜上的毒力及其在基本培养基中的生长，表明HisDAc是组氨酸生物合成所必需的，而组氨酸生物合成有助于毒力和生长。比较蛋白质组学分析表明，HisDAc不仅参与氨基酸代谢，还参与其他生物学机制，包括细胞壁/膜/包膜功能。这表明HisDAc可能具有多效性作用。还证实，当大肠杆菌与Ac菌株在水中共同培养时，在存在突变体的情况下大肠杆菌的群体水平增加，而在存在野生型菌株的情况下则没有增加。本研究为与初级代谢产物产生相关的酶提供了新的见解，并为发现一种控制BFB的抗毒力试剂提供了一个有前景的靶点。
