Comparative Metabolome and Transcriptome Analyses of Susceptible Asparagus officinalis and Resistant Wild A. kiusianus Reveal Insights into Stem Blight Disease Resistance

Phomopsis asparagi is one of the most serious fungal pathogens, which causes stem blight disease in Asparagus officinalis (AO), adversely affecting its production worldwide. Recently, the development of novel asparagus varieties using wild Asparagus genetic resources with natural P. asparagi resistance has become a priority in Japan due to the lack of resistant commercial AO cultivars. In this study, comparative metabolome and transcriptome analyses of susceptible AO and resistant wild Asparagus kiusianus (AK) 24 and 48 h postinoculated (AOI_24 hpi, AOI_48 hpi, AKI_24 hpi and AKI_48 hpi, respectively) with P. asparagi were conducted to gain insights into metabolic and expression changes associated with AK species. Following infection, the resistant wild AK showed rapid metabolic changes with increased levels of flavonoids and steroidal saponins and decreased asparagusic acid glucose ester content, compared with the susceptible AO plants. Transcriptome data revealed a total of 21  differentially expressed genes (DEGs) as the core gene set that displayed upregulation in the resistant AK versus susceptible AO after infection with P. asparagi. Kyoto Encyclopedia of Genes and Genomes pathway analysis of these DEGs identified 11 significantly enriched pathways, including flavonoid biosynthesis and primary metabolite metabolism, in addition to plant signaling and defense-related pathways. In addition, comparative single-nucleotide polymorphism and Indel distributions in susceptible AO and resistant AK plants were evaluated using the latest AO reference genome Aspof.V1. The data generated in this study are important resources for advancing Asparagus breeding programs and for investigations of genetic linkage mapping, phylogenetic diversity and plant defense-related genes.