Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base, Ministry of Science and Technology/Key Laboratory for Control Technology and Standard for Agro-product Safety and Quality, Ministry of Agriculture and Rural Affairs/Key Laboratory for Agro-product Safety Risk Evaluation (Nanjing), Ministry of Agriculture and Rural Affairs/Collaborative Innovation Center for Modern Grain Circulation and Safety/Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014, Jiangsu, P. R. China.
School of Food and Biological Engineering, Jiangsu Univeristy, Zhenjiang, 212013, Jiangsu, P. R. China.
J Microbiol. 2019 Aug;57(8):694-703. doi: 10.1007/s12275-019-9123-6. Epub 2019 May 11.
Dihydroxyacid dehydratase (DHAD), encoded by ILV3, catalyses the third step in the biosynthetic pathway of branched-chain amino acids (BCAAs), which include isoleucine (Ile), leucine (Leu), and valine (Val). Enzymes involved in BCAA biosynthesis exist in bacteria, plants, and fungi but not in mammals and are therefore attractive targets for antimicrobial or herbicide development. In this study, three paralogous ILV3 genes (FgILV3A, FgILV3B, and FgILV3C) were identified in the genome of Fusarium graminearum, the causal agent of Fusarium head blight (FHB). Deletion of FgILV3A alone or combined with FgILV3B or FgILV3C indicated an important role for FgILV3A in BCAA biosynthesis. FgILV3A deletion mutants lost the ability to grow on medium lacking amino acids. Exogenous supplementation of 1 mM Ile and Val rescued the auxotrophy of ΔFgIlv3A, though 5 mM was required to recover the growth defects in ΔFgIlv3AB and ΔFgIlv3AC strains, indicating that FgIlv3b and FgIlv3c exhibit redundant but accessory roles with FgIlv3a in BCAA biosynthesis. The auxotrophy of ΔFgIlv3A resulted in pleiotropic defects in aerial hyphal growth, in conidial formation and germination, and in aurofusarin accumulation. In addition, the mutants showed reduced virulence and deoxynivalenol production. Overall, our study demonstrates that FgIlv3a is crucial for BCAA biosynthesis in F. graminearum and a candidate fungicide target for FHB management.
二羟酸脱水酶（DHAD）由 ILV3 编码，催化支链氨基酸（BCAAs）生物合成途径的第三步，包括异亮氨酸（Ile）、亮氨酸（Leu）和缬氨酸（Val）。BCAA 生物合成中涉及的酶存在于细菌、植物和真菌中，但不存在于哺乳动物中，因此是开发抗菌或除草剂的有吸引力的目标。在这项研究中，在禾谷镰刀菌的基因组中鉴定出三个同源的 ILV3 基因（FgILV3A、FgILV3B 和 FgILV3C），禾谷镰刀菌是赤霉病（FHB）的病原体。单独缺失 FgILV3A 或与 FgILV3B 或 FgILV3C 联合缺失表明 FgILV3A 在 BCAA 生物合成中起着重要作用。FgILV3A 缺失突变体丧失了在缺乏氨基酸的培养基中生长的能力。外源性补充 1mM Ile 和 Val 挽救了 ΔFgIlv3A 的营养缺陷型，但需要 5mM 才能恢复 ΔFgIlv3AB 和 ΔFgIlv3AC 菌株的生长缺陷，表明 FgIlv3b 和 FgIlv3c 在 BCAA 生物合成中与 FgIlv3a 具有冗余但辅助作用。ΔFgIlv3A 的营养缺陷型导致气生菌丝生长、分生孢子形成和萌发以及金毒素积累的多效缺陷。此外，突变体表现出降低的毒力和脱氧雪腐镰刀菌烯醇的产生。总的来说，我们的研究表明 FgIlv3a 对禾谷镰刀菌的 BCAA 生物合成至关重要，是赤霉病管理的候选杀菌剂靶标。
