Prabhu S Ashok, Naicker Previn, Duong Tuan A, Govender Ireshyn Selvan, Engelbrecht Juanita, Backer Robert, Stoychev Stoyan Hristov, van den Berg Noëlani
Hans Merensky Chair in Avocado Research, University of Pretoria, Pretoria, South Africa.
Department of Biochemistry, Genetics and Microbiology, Faculty of Natural and Agricultural Sciences, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria, South Africa.
Front Microbiol. 2025 Aug 25;16:1632726. doi: 10.3389/fmicb.2025.1632726. eCollection 2025.
Phytophthora root rot caused by the hemibiotrophic oomycete, is a major biotic hindrance in meeting the ever-increasing demand for avocados. In addition, the pathogen is a global menace to agriculture, horticulture and forestry. Phosphite trunk injections and foliar sprays remain the most effective chemical management strategy used in commercial avocado orchards against the pathogen. Phosphite is known to counter both directly and indirectly through fortification of host defense. However, phosphite's direct mode of action is still not understood completely. This study identified a isolate GKB4 sensitive to phosphite (EC of 27.9 μg/mL) and investigated the direct impact of phosphite on this isolate through label-free quantitative SWATH-MS. Proteomics data analysis of untreated vs. phosphite-treated samples revealed that the xenobiotic affects the pathogen's growth by targeting the oxidoreductases whose abundance is significantly reduced. Further, perturbations in the energy metabolism and membrane/transmembrane proteins and transporters, and oxidative stress contribute to growth inhibition. The current study also identified increased putrescine biosynthesis, a polyamine, that when present at non-optimal concentrations could be cytostatic/cytotoxic. The differential expression of enzymes involved in the biosynthesis of secondary metabolites and the intermediates/precursors involved in their biosynthesis is an interesting finding that needs further investigation to ascertain their role in phosphite-induced stress. The pathogen's attempt to counter phosphite's growth-inhibitory effects-through upregulation of alternate bioenergetics pathways (amino acid catabolism and β-oxidation of fatty acids), mitochondrial translation and translocation machinery, peroxisomal proteins, and antioxidants-appears ineffective. This research furthers our limited understanding of the direct effects of phosphite on and has identified potential candidates for molecular functional investigation.
由半活体营养型卵菌引起的疫霉根腐病，是满足对鳄梨不断增长需求的主要生物障碍。此外，该病原体对农业、园艺和林业构成全球威胁。亚磷酸盐树干注射和叶面喷雾仍然是商业鳄梨果园用于对抗该病原体的最有效化学管理策略。已知亚磷酸盐可通过增强宿主防御直接和间接发挥作用。然而，亚磷酸盐的直接作用方式仍未完全了解。本研究鉴定出一株对亚磷酸盐敏感的分离株GKB4（EC为27.9μg/mL），并通过无标记定量SWATH-MS研究了亚磷酸盐对该分离株的直接影响。未处理与亚磷酸盐处理样品的蛋白质组学数据分析表明，这种外源化合物通过靶向丰度显著降低的氧化还原酶来影响病原体的生长。此外，能量代谢、膜/跨膜蛋白和转运蛋白的扰动以及氧化应激导致生长抑制。本研究还发现腐胺生物合成增加，腐胺是一种多胺，当其浓度非最佳时可能具有细胞生长抑制/细胞毒性作用。参与次生代谢物生物合成的酶及其生物合成过程中的中间体/前体的差异表达是一个有趣发现，需要进一步研究以确定它们在亚磷酸盐诱导的应激中的作用。病原体试图通过上调替代生物能途径（氨基酸分解代谢和脂肪酸β氧化）、线粒体翻译和转运机制、过氧化物酶体蛋白和抗氧化剂来对抗亚磷酸盐的生长抑制作用，但似乎无效。这项研究进一步加深了我们对亚磷酸盐直接作用的有限理解，并确定了分子功能研究的潜在候选对象。
