FcLRR1 Regulates Hyphal Growth and Plant Infection in Fusarium circinatum

Pitch canker caused by the fungus Fusarium circinatum is a destructive disease that affects pines in Europe, South Africa, and North America, particularly along the southeastern and western coasts of the United States. This study systematically elucidated the function of the Leucine-rich repeat (LRR) protein FcLRR1 in the pine pitch canker pathogen Fusarium circinatum. A total of 13 LRR proteins were identified via bioinformatic analysis. Using a gene knockout system, we demonstrated that deletion of FcLRR1 significantly impaired vegetative growth, conidiation, and conidium germination; led to a complete loss of macroconidia production; and drastically reduced abiotic stress tolerance and virulence. Transcriptome profiling revealed 612 downregulated genes, which were significantly enriched in pathways such as starch and sucrose metabolism, indicating that FcLRR1 modulated energy supply and pathogenicity through carbon source utilization. Through genome-wide protein structure modeling and yeast two-hybrid assays, we identified and validated the interaction between FcLRR1 and ALG-11, among other candidate proteins, further supporting its involvement in carbon metabolism, cell wall integrity, and pathogenesis. This study represents the first functional characterization of an LRR-containing protein in a forest pathogenic fungus and provides a foundational basis for developing targeted disease control strategies.