Integrative transcriptomic and metabolomic analysis elucidates the regulatory role of VmSDG1 in secondary metabolism of Valsa mali
Yuan, Weiwei ; Zheng, Dian ; Liu, Hailong ; Tian, Xiangrong ; Meng, Yangguang ; Xu, Liangsheng ; Huang, Lili
DOI 10.1016/j.pmpp.2026.103216
Abstract
Apple Valsa canker (AVC), caused by Valsa mali (syn. Cytospora mali), is a destructive disease of apple trees in East Asia. While non-ribosomal peptide synthetases (NRPSs) are known virulence regulators in plant-pathogenic fungi, their specific roles in V. mali remain underexplored. We characterized an NRPS-like gene, VmSDG1, previously linked to the synthesis of a necrosis-inducing cyclic dipeptide, SDP1. To investigate its broader function, we compared wild-type strain 03-8 with a Delta VmSDG1 mutant using transcriptomic and metabolomic analyses. Transcriptome sequencing across four infection time points (0, 6, 12, and 24 hpi) revealed 61 genes consistently differentially expressed between the wild-type and mutant, while metabolome analysis of fermentation broths at 15 days post-inoculation identified 78 significantly differentially accumulated metabolites. Notably, unlike typical NRPS genes that function in a pathway-specific manner, VmSDG1 exerts broad regulatory effects on primary and secondary metabolism, as evidenced by co-enrichment of differentially expressed genes and metabolites in 14 KEGG pathways, including three key pathways: tryptophan metabolism, tyrosine metabolism, and phenylalanine metabolism. Within tryptophan metabolism, we found that the content of picolinic acid-the end product of the kynurenine pathway-was significantly reduced by approximately 20% in the Delta VmSDG1 mutant. Moreover, the exogenous application of picolinic acid has been confirmed to have phytotoxic effects on apple leaves. Elucidating NRPS-linked metabolic networks provides new insight into AVC pathogenicity and may inform targeted disease management strategies.