3.6 Identification and functional enrichment analysis of DAMs
The samples at 24 hpi were further selected for widely targeted
metabolome analysis. A total of 910 metabolites were identified, which
could be divided into 11 classes
(Figure 4A and Supplementary Table
5). Among them, flavonoids were the largest group, accounting for
22.53% of the total identified metabolites. Less variations were
observed among biological replicates for each sample, but there were
great variations between samples of Payzawat and PI511890 based on PCA
analysis (Figure 4B).
A total of 132 DAMs (83 up-regulated and 49 down-regulated) were induced
in PI511890 by GSB pathogen inoculation
(Figure 4C), and 153 DAMs (73
up-regulated and 80 down-regulated) were detected in Payzawat. There
were 36 DAMs commonly detected in PI511890 and Payzawat after GSB
pathogen infection (Figure 4D). Interestingly, there were six DAMs
showing completely opposite accumulation patterns in Payzawat and
PI511890 (Figure
5A). Among them, oxalic acid and
methyl caffeate were reported to be involved in disease resistance. The
accumulation of oxalic acid was increased in resistant PI5111890 while
decreased in susceptible Payzawat after GSB pathogen inoculation. An
opposite accumulation pattern was observed for methyl caffeate. These
results suggested that methyl caffeate is probably not directly involved
in the GSB resistance. However, oxalic acid has the potential to be used
as a marker metabolite for GSB resistance in melon, especially at the
early stage.