Yuan Zhixiang, Yu Yijie, Yang Tingmi, Xue Yuwei, Hu Jiangfei, Wambui Njoroge Hellen, Liu Zhuang, Wang Mingzhao, Liu Hongxia
State Key Laboratory of Agricultural and Forestry Biosecurity, Nanjing Agricultural University, Nanjing, China.
Changzhou Institute of Materia Medica Co., Ltd, Changzhou, China.
Mol Plant Pathol. 2025 Jul;26(7):e70118. doi: 10.1111/mpp.70118.
Pectobacterium actinidiae is one of the primary pathogens that causes summer canker disease in kiwifruit, yet its pathogenic mechanisms remain unknown. The exopolysaccharide PCAP-1a, isolated from the fermentation broth of P. actinidiae strain GX1, exhibits notable cytotoxicity and acts as a virulence factor facilitating host infection. Genome-wide analysis revealed a 21-gene cluster responsible for the biosynthesis of exopolysaccharides in GX1. Homologous recombination was used to systematically knock out these genes, which led to the identification of RmlA as a key protein in the synthesis of the PCAP-1a precursor. The deletion of the rmlA gene significantly affected the yield of PCAP-1a and resulted in a direct reduction in GX1 pathogenicity. Further studies revealed that mutations in the substrate binding site of RmlA weakened its capacity to bind G-1-P and dTTP, which led to markedly reduced pathogenicity in the corresponding complemented strains. This study indicates that the exopolysaccharide PCAP-1a serves as a virulence factor in the pathogenesis of GX1, and its biosynthesis depends on the polysaccharide synthesis gene rmlA and the substrate binding activity of its encoded protein.
猕猴桃溃疡病菌是导致猕猴桃夏季溃疡病的主要病原菌之一，但其致病机制尚不清楚。从猕猴桃溃疡病菌株GX1发酵液中分离得到的胞外多糖PCAP-1a具有显著的细胞毒性，是促进宿主感染的毒力因子。全基因组分析揭示了GX1中一个负责胞外多糖生物合成的21个基因的簇。利用同源重组系统敲除这些基因，从而鉴定出RmlA是PCAP-1a前体合成中的关键蛋白。rmlA基因的缺失显著影响了PCAP-1a的产量，并直接导致GX1致病性降低。进一步研究表明，RmlA底物结合位点的突变削弱了其与G-1-P和dTTP结合的能力，导致相应互补菌株的致病性显著降低。本研究表明，胞外多糖PCAP-1a在GX1致病过程中作为毒力因子，其生物合成依赖于多糖合成基因rmlA及其编码蛋白的底物结合活性。
