Structural and Phylogenetic Characterization of Polygalacturonase Genes Pg1 and Pgx1 from Two Fusarium Oxysporum Isolates Causing Wilt in Pea and Tomato

Fusarium oxysporum possesse a significant threat to many vegetables, including pea (Pisum sativum) and tomato (Solanum lycopersicum), causing vascular wilt. Two F. oxysporum isolates, FP and FT, were isolated from wilted pea and tomato plants in fields with a 90% disease incidence. The identity of the isolates was confirmed through conidia morphology, multi-locus phylogeny (ITS, LSU, Ef1 alpha) and pathogenicity assays. Both exhibited strong pectinolytic activity, with the F. oxysporum FT isolate showing a higher degradation index. Full-length sequences of endo-polygalacturonase (pg1) and exo-polygalacturonase (pgx1) genes were cloned, sequenced and analysed to assess structural variation and phylogenetic relationships. The pg1 displayed greater sequence variation than the pgx1. Both genes exhibited high sequence similarity with known pathogenic F. oxysporum strains and distinct polymorphisms among other Fusarium species. Homology modelling and molecular dynamics simulations confirmed the structural and functional stability of PG1 and PGX1 proteins, with a predicted active site for substrate binding supporting roles in infection. This study provides structural and phylogenetic insights into the F. oxysporum polygalacturonases and the efficiency of the enzymes for the degradation of pectic substances of the host tissue for penetration and establishment of infection into the host.