Abstract
BackgroundCitrus flavonoids are considered as the important secondary metabolites because of their biological and pharmacological activities. Chalcone synthase (CHS) is a key enzyme that catalyses the first committed step in the flavonoid biosynthetic pathway. CHS genes have been isolated and characterized in many plants. Previous studies indicated that CHS is a gene superfamily. In citrus, the number of CHS members and their contribution to the production of flavonoids remains a mystery. In our previous study, the copies of CitCHS2 gene were found in different citrus species and the sequences are highly conserved, but the flavonoid content varied significantly among those species.ResultsFrom seventy-seven CHS and CHS-like gene sequences, ten CHS members were selected as candidates according to the features of their sequences. Among these candidates, expression was detected from only three genes. A predicted CHS sequence was identified as a novel CHS gene. The structure analysis showed that the gene structure of this novel CHS is very similar to other CHS genes. All three CHS genes were highly conserved and had a basic structure that included one intron and two exons, although they had different expression patterns in different tissues and developmental stages. These genes also presented different sensitivities to methyl jasmonate (MeJA) treatment. In transgenic plants, the expression of CHS genes was significantly correlated with the production of flavonoids. The three CHS genes contributed differently to the production of flavonoids.ConclusionOur study indicated that CitCHS is a gene superfamily including at least three functional members. The expression levels of the CHS genes are highly correlated to the biosynthesis of flavonoids. The CHS enzyme is dynamically produced from several CHS genes, and the production of total flavonoids is regulated by the overall expression of CHS family genes.
Highlights
Citrus flavonoids are considered as the important secondary metabolites because of their biological and pharmacological activities
Phylogenetic analysis of the Chalcone synthase (CHS) family genes The CHS gene has been reported to be a member of the PKS (Polyketide synthase) superfamily in plants [37]
A phylogenetic tree of the CHS family genes was constructed using the ClustalW method based on the substitution of amino acid residues of the CHS and CHS-like genes derived from citrus genome sequence databases (NCBI, Phytozome and Orange Genome Annotation Project)
Summary
Citrus flavonoids are considered as the important secondary metabolites because of their biological and pharmacological activities. The copies of CitCHS2 gene were found in different citrus species and the sequences are highly conserved, but the flavonoid content varied significantly among those species. Flavonoids consist of over 7000 compounds and represent a large class of plant secondary metabolites [1,2,3]. More than 60 flavonoid compounds have been identified in citrus. Those flavonoids can be classified into four major types of substances named flavones, flavonols, flavanones, and flavanonols according to their basic structures [14, 15].
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