Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, P.R. China.
Department of Plant Pathology, University of Georgia, Tifton, GA, U.S.A.
Mol Plant Microbe Interact. 2023 Mar;36(3):176-188. doi: 10.1094/MPMI-08-22-0165-R. Epub 2023 Mar 9.
Onion center rot is caused by at least four species of genus (, , , and subsp). Critical onion pathogenicity determinants for were recently described, but whether those determinants are common among other onion-pathogenic species remains unknown. In this work, we report onion pathogenicity determinants in subsp and We identified two distinct secondary metabolite biosynthetic gene clusters present separately in different strains of onion-pathogenic subsp. One cluster is similar to the previously described HiVir phosphonate biosynthetic cluster identified in and another is a novel putative phosphonate biosynthetic gene cluster, which we named Halophos. The Halophos gene cluster was also identified in strains. Both clusters are predicted to be phosphonate biosynthetic clusters based on the presence of a characteristic phosphoenolpyruvate phosphomutase () gene. The deletion of the gene from either HiVir or Halophos clusters in subsp. caused loss of necrosis on onion leaves and red onion scales and resulted in significantly lower bacterial populations compared with the corresponding wild-type and complemented strains. Seven ( to ) of 11 genes ( to ) in the Halophos gene cluster are required for onion necrosis phenotypes. The onion nonpathogenic strain PNA15-2 ( subsp. ) gained the capacity to cause foliar necrosis on onion via exogenous expression of a minimal seven-gene Halophos cluster (genes to . Furthermore, cell-free culture filtrates of PNA14-12 expressing the intact Halophos gene cluster caused necrosis on onion leaves consistent with the presence of a secreted toxin. Based on the similarity of proteins to those with experimentally determined functions, we are able to predict most of the steps in Halophos biosynthesis. Together, these observations indicate that production of the toxin phosphonate seems sufficient to account for virulence of a variety of different strains, although strains differ in possessing a single but distinct phosphonate biosynthetic cluster. Overall, this is the first report of onion pathogenicity determinants in subsp and [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
洋葱中心腐烂是由至少四个种属的物种引起的(、、、和 subsp)。最近描述了洋葱致病的关键决定因素，但这些决定因素是否在其他洋葱致病种属中普遍存在尚不清楚。在这项工作中，我们报告了洋葱致病决定因素在 subsp 和 我们在不同的洋葱致病 subsp 菌株中分别鉴定出两个不同的次生代谢物生物合成基因簇。一个簇与先前在 中描述的 HiVir 膦酸盐生物合成簇相似，另一个是新型的可能的膦酸盐生物合成基因簇，我们将其命名为 Halophos。Halophos 基因簇也在 菌株中被鉴定出来。这两个簇都基于特征性的磷酸烯醇丙酮酸磷酸变位酶()基因的存在，被预测为膦酸盐生物合成簇。从洋葱致病 subsp 的 HiVir 或 Halophos 簇中删除 基因会导致洋葱叶片和红洋葱鳞片坏死，并导致与相应的野生型和互补菌株相比，细菌数量显著减少。Halophos 基因簇的 11 个基因(至)中有 7 个(至)需要洋葱坏死表型。非致病洋葱菌株 PNA15-2(subsp.)通过外源性表达最小的七个基因 Halophos 簇(基因 至)获得了在洋葱上引起叶坏死的能力。此外，表达完整 Halophos 基因簇的 PNA14-12 的无细胞培养滤液在洋葱叶片上引起坏死，这与分泌毒素的存在一致。基于与具有实验确定功能的蛋白的相似性，我们能够预测 Halophos 生物合成的大部分步骤。总的来说，这些观察结果表明，毒素膦酸盐的产生似乎足以解释各种不同 菌株的毒力，尽管菌株在拥有单个但独特的膦酸盐生物合成簇方面存在差异。总的来说，这是第一次在 subsp 和 中报道洋葱致病决定因素。
