Abstract
The plant metabolome is considered as a bridge between the genome and the phenome and is essential for the interaction between plant growth and the plant environment. Here, we used the liquid chromatography-tandem mass spectrometry method to perform a widely targeted metabolomics analysis of 150 millet germplasm and simultaneous identification and quantification of 330 annotated metabolites. Comparing the metabolic content of different millets revealed significant natural variation of both primary and secondary metabolites, including flavonoids, phenolamides, hydroxycinnamoyl derivatives, nucleotides, and lipids, in the millets from India and the north and south of China; among them, some of the flavonoids are the most prominent. A total of 2.2 TB sequence data were obtained by sequencing 150 accessions of foxtail millet using the Illumina platform. Further digging into the genetic basis of metabolites by mGWAS analysis found that cyanidin 3-O-glucoside and quercetin O-acetylhexside are concentratedly located at 43.55 Mb on chromosome 5 and 26.9 Mb on chromosome 7, and two Lc were mined as candidate genes, respectively. However, the signals of luteolin 7-O-glucoside and kaempferol 3-O-glucoside were also detected at 14.36 Mb on chromosome 3, and five glycosyltransferase genes on this loci were deemed to regulate their content. Our work is the first research to use mGWAS in millet, and it paves the way for future dissection of complex physiological traits in millet.
Highlights
As a healthy food material for the development of functional foods and natural antioxidant resources, foxtail millet (Setaria italica) is an important grain crop
We identified 155 primary metabolites, including 31 amino acids with their derivatives, 24 nucleotides and their derivatives, 5 carbohydrates, 23 organic acids, and 72 lipids, and a number of secondary metabolites, including 42 flavone O-glycosides, 22 flavone C-glycosides, 13 flavonol O-glycosides, 9 flavanones, 6 anthocyanins, 6 flavonolignans, 12 hydroxycinnamic acid derivatives, 11 hydroxycinnamoyl quinates, 15 phenolamides, 5 phytohormones, 14 benzoic acid derivatives, 4 coumarins, 3 alkaloids, 4 vitamins, and 9 others (Supplementary Figure 1A)
The metabolites in clade 5, clade 6, and clade 8, displayed lower levels in millet from the south and/or north of China when compared to the millet in India, and were mainly represented by C-glycosyl-flavone O-glycosides, flavone di-O-glycosides, nucleoside phosphate, and glycerophospholipids (Figure 1C), disclosing significant natural variation in both primary and secondary metabolites in millets from different areas
Summary
As a healthy food material for the development of functional foods and natural antioxidant resources, foxtail millet (Setaria italica) is an important grain crop. Investigation of the metabolome in rice and maize core collections has demonstrated significant natural variation of secondary metabolites, such as flavonoids, phenolamides, hydroxycinnamic acid derivatives, and terpenoids, in these species (Chen et al, 2014; Dong et al, 2014; Wen et al, 2014). Flavonoids, such as flavone mono-C-hexosides, malonylated flavone O-hexosides, and flavone 5-O-glycosides, accumulated in relevantly lower levels in the rice subspecies japonica than that in indica, while phenolamides, such as Np-coumaroyl spermidine and N-sinapoyl agmatine/putrescine, accumulated at significantly higher levels in japonica than in indica (Dong et al, 2014; Wen et al, 2014). Investigations of natural variation in metabolic traits, as well as their relationship with complex agronomic traits in foxtail millet are lacking
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