Transcriptome Analysis of Purple Pericarps in Common Wheat (Triticum aestivum L.)

Abstract

Wheat (Triticum aestivum L.) cultivars possessing purple grain arethought to be more nutritious because of high anthocyanin contents in the pericarp. Comparative transcriptome analysis of purple (cv Gy115) and white pericarps was carried out using next-generation sequencing technology. There were 23,642 unigenes significantly differentially expressed in the purple and white pericarps, including 9945 up-regulated and 13,697 down-regulated. The differentially expressed unigenes were mainly involved in encoding components of metabolic pathways, The flavonoid biosynthesis pathway was the most represented in metabolic pathways. In the transcriptome of purple pericarp in Gy115, most structural and regulatory genes biosynthesizing anthocyanin were identified, and had higher expression levels than in white pericarp. The largestunigene of anthocyanin biosynthesis in Gy115 was longer than the reference genes, which implies that high-throughput sequencing could isolate the genes of anthocyanin biosynthesis in tissues or organs with high anthocyanin content. Based on present and previous results, three unigenes of MYB gene on chromosome 7BL and three unigenes of MYC on chromosome 2AL were predicted as candidate genes for the purple grain trait. This article was the first to provide a systematic overview comparing the transcriptomes of purple and white pericarps in common wheat, which should be very valuable for identifying the key genes for the purple pericarp trait.

Fig 1. Distribution of lengths of the assembled unigenes in wheat pericarps.

Fig 2. Differentially expressed genes between opata and Gy115.

The genes were classified into three classes. Red genes are up-regulated if gene expression of right sample is larger than left sample. Green genes are down-regulated that gene expression of left sample is larger if right sample. Blue genes are not differentially expressed. The horizontal coordinates is the expression level of right and the vertical coordinates is the expression level of left sample.

Fig 3. Gene Ontology (GO) classifications of differentially expressed unigenes.

Unigenes were assigned to three categories: cellular components, molecular functions and biological process.

Fig 4. The expression differences of structural genes in the phenylalanine pathway.

Arrow shows the metabolic stream, abbreviation left or upward arrows represent the genes catalyzing the progress, the light abbreviation means these genes were found in assembly unigenes, the number represent the in crease time of the expression in purple pericarp against white pericarp.