Genome Analysis of Alternaria alstroemeriae L6 Associated with Black Spot of Strawberry: Secondary Metabolite Biosynthesis and Virulence

A pathogenic fungus was isolated from the leaves of strawberry black spot in Zhengzhou China. Based on morphological and phylogenetic analysis, the isolate was identified as <i>Alternaria alstroemeriae</i>. Hybrid sequencing and assembly yielded a high-quality 38.7 Mb genome with 12,781 predicted genes and 99.6% Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness. Functional annotation revealed enrichment in carbohydrate metabolism, secondary metabolite biosynthesis, and virulence-associated genes. Strain L6 harbored 45 biosynthetic gene clusters(BGCs), including 12 clusters for terpenes, 7 for non-ribosomal peptide synthetases, and 7 for polyketide synthases. Six BGCs showed high similarity to known pathways producing alternariol (phytotoxic/mycotoxic compound), alternapyrone (phytotoxin), choline (osmoprotectant), terpestacin (anti-angiogenic agent), clavaric acid (anticancer terpenoid), and betaenone derivatives (phytotoxins). CAZyme analysis identified 596 carbohydrate-active enzymes, aligning with L6's biotrophic lifestyle. Additionally, 996 secreted proteins were predicted, of which five candidate effectors contained the conserved RxLx [EDQ] host-targeting motif, suggesting potential roles in virulence. This genome resource highlights L6's exceptional secondary metabolites (SMs) diversity, featuring both plant-pathogenic toxins and pharmacologically valuable compounds, indicating that this endophytic fungus is a potential producer of metabolites meriting further exploration and development.