Abstract
BackgroundBroccoli (Brassica oleracea var. italica), a member of Cruciferae, is an important vegetable containing high concentration of various nutritive and functional molecules especially the anticarcinogenic glucosinolates. The sprouts of broccoli contain 10–100 times higher level of glucoraphanin, the main contributor of the anticarcinogenesis, than the edible florets. Despite the broccoli sprouts’ functional importance, currently available genetic and genomic tools for their studies are very limited, which greatly restricts the development of this functionally important vegetable.ResultsA total of ∼85 million 251 bp reads were obtained. After de novo assembly and searching the assembled transcripts against the Arabidopsis thaliana and NCBI nr databases, 19,441 top-hit transcripts were clustered as unigenes with an average length of 2,133 bp. These unigenes were classified according to their putative functional categories. Cluster analysis of total unigenes with similar expression patterns and differentially expressed unigenes among different tissues, as well as transcription factor analysis were performed. We identified 25 putative glucosinolate metabolism genes sharing 62.04–89.72% nucleotide sequence identity with the Arabidopsis orthologs. This established a broccoli glucosinolate metabolic pathway with high colinearity to Arabidopsis. Many of the biosynthetic and degradation genes showed higher expression after germination than in seeds; especially the expression of the myrosinase TGG2 was 20–130 times higher. These results along with the previous reports about these genes’ studies in Arabidopsis and the glucosinolate concentration in broccoli sprouts indicate the breakdown products of glucosinolates may play important roles in the stage of broccoli seed germination and sprout development.ConclusionOur study provides the largest genetic resource of broccoli to date. These data will pave the way for further studies and genetic engineering of broccoli sprouts and will also provide new insight into the genomic research of this species and its relatives.
Highlights
Consumption of fruits and vegetables has long been associated with better health and lower incidence of a variety of diseases such as coronary heart disease, cancers, etc [1,2]
The sequencing data has been deposited into national center for biotechnology information (NCBI) gene expression omnibus (GEO) and the accession number is GSE53298
Our study found that putative orthologs of bHLH56, PIF1, PIF3, PIF4, PIF5, PIL1, PIF7, SPT were expressed in broccoli seed germination and sprout development, suggesting their similar roles in light signaling during this period
Summary
Consumption of fruits and vegetables has long been associated with better health and lower incidence of a variety of diseases such as coronary heart disease, cancers, etc [1,2]. A diet rich in cruciferous vegetables especially broccoli Epidemiological studies prior to 1996 showed an inverse relationship between cancer risk and cruciferous vegetable intake [3,4]. Glucosinolates are a major group of sulfur-rich secondary metabolites in Cruciferae, which are well-known by their breakdown products to display several bioactivities, including plant defense against pathogens and insects as well as anticarcinogenesis in mammals [8]. Based on their precursor amino acids, glucosinolates are divided into three major categories: aliphatic, indolic and aromatic glucosinolates [9,10]. Despite the broccoli sprouts’ functional importance, currently available genetic and genomic tools for their studies are very limited, which greatly restricts the development of this functionally important vegetable
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