Histological and molecular responses of Vigna angularis to Uromyces vignae infection.

Background: To advance the understanding of adzuki bean (Vigna angularis) resistance to infection with the rust-causing fungus Uromyces vignae (Uv), we comprehensively analyzed histological events and the transcriptome of Uv-infected adzuki bean.

Results: Compared with the susceptible cv. Baoqinghong (BQH), the resistant cv. QH1 showed inhibition of uredospore germination and substomatal vesicle development, intense autofluorescence of cells around the infection site, and cell wall deposit formation in response to Uv infection. In cv. QH1, gene set enrichment analysis (GSEA) showed enrichment of chitin catabolic processes and responses to biotic stimuli at 24 h post-inoculation (hpi) and cell wall modification and structural constituent of cytoskeleton at 48 hpi. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated enrichment of WRKY transcription factors (TFs), the calcium binding protein cml, and hydroquinone glucosyltransferase at both 24 and 48 hpi. In total, 1992 and 557 differentially expressed genes (DEGs) were identified at 24 and 48 hpi, respectively. Cell surface pattern-recognition receptors (PRRs), WRKY TFs, defense-associated pathogenesis-related (PR) proteins, and lignin and antimicrobial phenolic compound biosynthesis were significantly induced. Finally, we detected the chitinase (CHI) and phenylalanine ammonia-lyase (PAL) activity were higher in QH1 and increased much earlier than in BQH.

Conclusion: In cv. QH1, cell-surface PRRs rapidly recognize Uv invasion and activate the corresponding TFs to increase the transcription of defense-related genes and corresponding enzymatic activities to prevent fungal development and spread in host tissues.