关键词: 谷子, 种子萌发吸水期, 转录物组分析, 苯丙烷生物合成途径, 苯丙氨酸代谢途径

Abstract:

【Objective】 Foxtail millet (Setaria italica L.) is a hardy cereal and known for its tolerance against drought and barrenness, which originated in China. In this study, the transcriptome of foxtail millet was analyzed in germinating seeds during different uptake of water phases, which is to get a lot of differently expressed genes, and find the important metabolic pathways, key genes and metabolites of regulating germination in foxtail millet. 【Method】The cDNA libraries of Jingu 20 were constructed in germinating seeds during rapid initial uptake of water, plateau phase, further increase in water uptake for the transcriptome analysis. The cluster analysis of gene expression was performed by K-Means. Differential expression analysis used DESeq. The functional annotations of differentially expressed genes were obtained by using COG, GO, KEGG, and so on. The key metabolism pathways and genes that regulated germination in foxtail millet were found during different water uptake phase through KEGG enrichment of DEGs. The reliability of sequencing results was confirmed by qRT-PCR. The contents of metabolites were assayed by HPLC.【Result】The genome-wide gene expression profile was obtained by RNA-sequencing during rapid initial uptake of water, plateau phase and further increase in water uptake. A total of 33 643 genes were expressed. Nine co-expression clusters with distinctive patterns were identified. There were 3 893, 4 612 and 8 472 DEGs in rapid initial uptake of water and plateau phase, plateau phase and further increase in water uptake, rapid initial uptake of water and further increase in water uptake, respectively. The KEGG pathway enrichment analysis showed that these DEGs of the three comparisons were significantly associated with phenylpropanoid biosynthesis,phenylalanine metabolism, starch and sucrose metabolism. The DEGs between rapid initial uptake of water and plateau phase, between rapid initial uptake of water and further increase in water uptake were also enriched in plant hormone signal transduction. And the number of genes enriched in the metabolism pathway of phenylpropanoid biosynthesis and phenylalanine metabolism was the largest in the three comparisons. The peroxidase genes had the highest proportion among these genes of the two pathways. The results obtained from four phenylpropanoids-related genes tested by qRT-PCR were consistent with the trend of regulation identified by gene expression profile. In dormant seeds of foxtail millet, there was the preformed mRNAs of 4-coumarate-CoA ligase 3, which displayed firstly decreasing, then increasing and finally declining patterns during the uptake of water stage. The contents of phenylpropanoids-related metabolites in germination seeds of foxtail millet indicated that large amounts of sinapic acid were stored in dormant seeds. During uptake of water by a dry seed, the content of sinapic acid gradually decreased, but those of p-coumaric acid, caffeic acid and ferulic acid increased first and then decreased. 【Conclusion】DEGs of foxtail millet were significantly related with phenylpropanoid biosynthesis and phenylalanine metabolism in germinating seeds during different uptake of water stages. The upstream and downstream genes of phenylpropanoid biosynthesis, such as 4-coumarate-CoA ligase 3 and peroxidase, played regulation roles in response to water during germination of foxtail millet. Sinapic acid participated in the dormancy and germination of millet seeds, which were the medium product of phenylpropanoid biosynthesis pathway.

Key words: foxtail millet, water uptake phase of seed germination, transcriptome analysis, phenylpropanoid biosynthesis, phenylalanine metabolism