The Essentials of PgPG1, a Polygalacturonase-Encoding Gene for the Invasion of Pyrenophora graminea to Hordeum vulgare

Barley leaf stripe, caused by <i>Pyrenophora graminea</i>, significantly reduces yield. Polygalacturonase, a key fungal pectinase, facilitates cell wall degradation for nutrition acquisition and colonization. To determine whether <i>P. graminea</i> contains polygalacturonase (<i>PgPG</i>)-encoding genes and their role in pathogenicity, four <i>PgPG</i> genes (<i>PgPG1</i>-<i>PgPG4</i>) were identified in the <i>P. graminea</i> genome. Quantitative RT-PCR revealed that <i>PgPG1</i> had the highest inducible expression during barley infection, suggesting its critical vital role in pathogenesis. <i>PgPG1</i> was silenced and overexpressed in <i>P. graminea</i> QWC (wild-type) using CaCl₂-PEG4000-mediated protoplast transformation. The <i>PgPG1</i> RNAi mutants exhibited slower growth, while overexpression mutants grew faster. Relative to the wild-type, the disease incidence of Alexis, a highly susceptible barley variety, decreased by 62.94%, 42.19%, 45.74%, and 40.67% for RNAi mutants, and increased by 12.73%, 12.10%, 12.63%, and 10.31% for overexpression mutants. Pathogenicity analysis showed decreased disease incidence with <i>PgPG1</i> RNAi mutants and increased severity with overexpression mutants. Trypan blue staining and polygalacturonase activity assays confirmed that overexpression mutants caused more severe damage compared to wild-type and RNAi mutants. These findings indicate that <i>PgPG1</i> plays a vital role in the pathogenicity of <i>P. graminea</i> in barley and has great potential as a pathogen target gene to develop a durable resistance variety to <i>P. graminea</i>.