A Novel Biosynthetic Gene Cluster Across the Pantoea Species Complex Is Important for Pathogenicity in Onion.
A Novel Biosynthetic Gene Cluster Across the Pantoea Species Complex Is Important for Pathogenicity in Onion.
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DOI：
10.1094/mpmi-08-22-0165-r
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发表时间：
2023-03
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洋葱中心腐烂病是由至少四种洋葱腐烂菌(P.ananatis、P.agregans、P.allii和P.stewartii subsp.)引起的。吲哚)。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的泛亚植物中是常见的仍不清楚。在这项工作中，我们报道了洋葱致病决定因素在P.stewartii亚种。吲哚青霉和大蒜青霉。我们鉴定了两个不同的次生代谢物生物合成基因簇，分别存在于不同的洋葱致病P.stewartii亚种中。消炎药。其中一个簇与已报道的磷酸盐生物合成簇相似，另一个簇是一个新的可能的磷酸酯生物合成基因簇，我们将其命名为Halophos。在蒜青霉菌株中也发现了Halophos基因簇。这两个簇都被预测为基于特征的磷酸烯醇式丙酮酸磷酸变位酶(PepM)基因的磷酸盐生物合成簇。P.stewartii亚种HiVir和Halophos簇中PepM基因的缺失。与相应的野生型和互补菌株相比，吲哚导致洋葱叶片和红洋葱鳞片的坏死损失，并导致细菌数量显著减少。在Halophos基因簇的11个基因(Hala-Halk)中，有7个(halb-halH)是洋葱坏死表型所必需的。洋葱非致病菌株PNA15-2(P.stewartii subsp.吲哚)通过外源表达最小的七个基因Halophos簇(halb-halH)获得了导致洋葱叶片坏死的能力。此外，表达完整的盐磷基因簇的PNA14-12的无细胞培养滤液引起洋葱叶片的坏死，这与分泌毒素的存在一致。基于蛋白质与那些具有实验确定的功能的蛋白质的相似性，我们能够预测盐磷生物合成的大部分步骤。总之，这些观察表明，磷酸盐毒素的产生似乎足以解释各种不同Pantoea菌株的毒力，尽管不同菌株拥有单一但不同的磷酸盐生物合成簇。总体而言，这是首次报道了洋葱致病因子在P.stewartii亚种。吲哚青霉和大蒜青霉。
Onion center rot is caused by at least four species of Pantoea (P. ananatis, P. agglomerans, P. allii, and P. stewartii subsp. indologenes). Critical onion pathogenicity determinants for P. ananatis were recently described but whether those determinants are common among other onion-pathogenic Pantoea species remains unknown. In this work, we report onion pathogenicity determinants in P. stewartii subsp. indologenes and P. allii. We identified two distinct secondary metabolite biosynthetic gene clusters present separately in different strains of onion pathogenic P. stewartii subsp. indologenes. One cluster is similar to the previously described HiVir phosphonate biosynthetic cluster identified in P. ananatis and another is a novel putative phosphonate biosynthetic gene cluster, which we named “Halophos”. The Halophos gene cluster was also identified in P. allii strains. Both clusters are predicted to be phosphonate biosynthetic clusters based on the presence of a characteristic phosphoenolpyruvate phosphomutase (pepM) gene. The deletion of pepM gene from either HiVir or Halophos clusters in the P. stewartii subsp. indologenes caused loss of necrosis on onion leaves and red onion scales, and resulted in significantly lower bacterial populations compared to the corresponding wildtype and complemented strains. Seven (halB-halH) out of eleven genes (halA-halK) in the Halophos gene cluster are required for onion necrosis phenotypes. The onion non-pathogenic strain PNA15–2 (P. stewartii subsp. indologenes) gained the capacity to cause foliar necrosis on onion via exogenous expression of a minimal seven gene Halophos cluster (halB –halH). 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 Pantoea strains, although strains differ in possessing a single but distinct phosphonate biosynthetic cluster. Overall, this is the first report of onion pathogenicity determinants in P. stewartii subsp. indologenes and P. allii.