Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Sciences, Cornell University, Ithaca, NY 14853, U.S.A.
Mol Plant Microbe Interact. 2018 Dec;31(12):1291-1300. doi: 10.1094/MPMI-04-18-0077-R. Epub 2018 Oct 24.
Pantoea ananatis, a cause of center rot of onion, is problematic in the United States and elsewhere. The bacterium lacks disease determinants common to most other bacterial pathogens of plants. A genomic island containing the gene pepM was detected within many onion-pathogenic strains of P. ananatis of diverse origins. The pepM gene of P. ananatis putatively encodes a protein that converts phosphoenolpyruvate to phosphonopyruvate, the first step in the biosynthesis of phosphonates and related molecules. This gene appears to be essential for center rot disease. Deletion of pepM rendered the mutant strain unable to cause lesions in leaves of growing onions and water-soaking of inoculated yellow onion bulbs. Furthermore, growth of the deletion mutant in onion leaves was significantly diminished compared with wild-type bacteria, and the mutant failed to cause cell death in tobacco. Complementation of the mutated strain with pepM restored the phenotype to wild-type capability. The pepM gene is the first pathogenicity factor identified that affects bacterial fitness as well as symptom development in both leaves and bulbs in a pathogen causing center rot of onion.
洋葱心腐病病原菌泛菌（Pantoea ananatis）在美国和其他地区造成了严重问题。该细菌缺乏大多数其他植物病原菌常见的疾病决定因素。在不同来源的多种洋葱致病性泛菌菌株中检测到一个含有 pepM 基因的基因组岛。泛菌的 pepM 基因可能编码一种将磷酸烯醇丙酮酸转化为磷烯丙氨酸的蛋白质，这是磷烷酸及其相关分子生物合成的第一步。该基因似乎对心腐病的发生是必需的。pepM 基因缺失使突变菌株无法在生长中的洋葱叶片上引起病变，也无法使接种的黄洋葱鳞茎水渍。此外，与野生型细菌相比，突变体在洋葱叶片上的生长明显减少，并且突变体不能引起烟草细胞死亡。用 pepM 基因对突变株进行互补恢复了表型，使其具有野生型的能力。pepM 基因是第一个鉴定出的致病性因子，它影响了导致洋葱心腐病的病原菌在叶片和鳞茎中细菌适应性和症状发展。
