Figure 5 KEGG enrichment
analysis of DAMs and in-depth analysis of key metabolites. A :
Six DAMs (a-f) with opposite accumulation patterns in Payzawat and
PI511890. The horizontal axis indicates the value of
log2FoldChange. Blue bars represent the down-regulated
DAMs. Orange bars represent
up-regulated DAMs. B : Flavonoids specifically accumulated in
Payzawat and PI511890 after GSB pathogen infection. C : KEGG
enrichment analysis for DAMs. MRT and MST represent the samples of GSB
pathogen inoculated PI511890 and Payzawat, respectively. MRC and MSC
represent the controls of PI511890 and Payzawat, respectively.
3.7 Integration of
transcriptome and metabolome profiles
To systematically understand the defense response of melon to GSB
at both
transcriptomic
and metabolic levels, an integrated
transcriptome and metabolome
analysis was performed. A total of eight and 18 KEGG pathways were
significantly enriched in transcriptome and metabolome in PI511890 after
infection, respectively (Figure 6A). However, only phenylpropanoid
biosynthesis and flavonoid biosynthesis were commonly enriched for both
DEGs and DAMs in PI511890 after infection. Similarly, a total of 21 and
20 KEGG pathways were enriched for DEGs and DAMs in Payzawat after
infection, respectively (Figure 6A). Several pathways, including amino
acid metabolism (alanine, aspartate and glutamate metabolism,
phenylalanine metabolism, butanoate metabolism, glutathione metabolism),
carbohydrate metabolism (pentose phosphate pathway, glyoxylate and
dicarboxylate metabolism), and biosynthesis of other secondary
metabolites (phenylpropanoid biosynthesis, phenylalanine, tyrosine and
tryptophan biosynthesis, flavone and flavonol biosynthesis), were
commonly enriched in transcriptome and metabolome in Payzawat after
infection.
Since phenylpropanoid biosynthesis was the only pathway commonly
enriched for DEGs and DAMs in both PI511890 and Payzawat after GSB
pathogen infection, the profiles of genes and metabolites in this
pathway were further analyzed (Figure 6). Except for the gene encoding
chalcone isomerase (MELO3C016680.2 ) that was down regulated in
PI511890, the other genes were mainly upregulated in both PI511890 and
Payzawat after GSB pathogen infection. Accumulation of lignins decreased
in PI511890 but not changed in Payzawat. Accumulation of
eriodictyol specifically increased
in PI511890, while apigenin specifically increased in Payzawat.
Furthermore, glyoxylate and
dicarboxylate metabolism and metabolic pathways were also enriched in
transcriptome and metabolome, in which the accumulation of oxalic acid
in PI511890 was significantly upregulated in glyoxylate cycle and citric
acid cycle (TCA cycle)
(Supplementary Figure 5,
Supplementary Figure 6). These results demonstrated that eriodictyol and
oxalic acid have the potential to be used as marker metabolites for GSB
resistance in melon. Moreover, the inconsistency of gene expression
patterns and the related metabolite accumulation patterns suggested that
post-transcription regulation is widely involved in the defense response
of melon to GSB.