Abstract
BackgroundThe external colour of fruit is a crucial quality feature, and the external coloration of most citrus fruits is due to the accumulation of carotenoids. The molecular regulation of carotenoid biosynthesis and accumulation in pericarp is limited due to the lack of mutant. In this work, an orange-pericarp mutant (MT) which showed altered pigmentation in the pericarp was used to identify genes potentially related to the regulation of carotenoid accumulation in the pericarp.ResultsHigh Performance Liquid Chromatography (HPLC) analysis revealed that the pericarp from MT fruits had a 10.5-fold increase of β-carotene content over that of the Wild Type (WT). Quantitative real-time PCR (qRT-PCR) analysis showed that the expression of all downstream carotenogenic genes was lower in MT than in WT, suggesting that down-regulation is critical for the β-carotene increase in the MT pericarp. RNA-seq analysis of the transcriptome revealed extensive changes in the MT gene expression level, with 168 genes down-regulated and 135 genes up-regulated. Gene ontology (GO) and KEGG pathway analyses indicated seven reliable metabolic pathways are altered in the mutant, including carbon metabolism, starch and sucrose metabolism and biosynthesis of amino acids. The transcription factors and genes corresponding to effected metabolic pathways may involved in the carotenoid regulation was confirmed by the qRT-PCR analysis in the MT pericarp.ConclusionsThis study has provided a global picture of the gene expression changes in a novel mutant with distinct color in the fruit pericarp of pummelo. Interpretation of differentially expressed genes (DEGs) revealed new insight into the molecular regulation of β-carotene accumulation in the MT pericarp.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0435-3) contains supplementary material, which is available to authorized users.
Highlights
The external colour of fruit is a crucial quality feature, and the external coloration of most citrus fruits is due to the accumulation of carotenoids
The colourless phytoene is converted into the red lycopene by four desaturation reactions and by two isomerization reactions mediated by carotene isomerase (CRTISO) and 15cis-ζ-carotene isomerase (ZISO)
Overexpression of a Vitis vinifera R2R3-MYB transcription factor (MYB5b) in tomato resulted in an increased content of β-carotene [57]. These results indicated that the MYB genes may be involved in regulating carotenoid biosynthesis
Summary
The external colour of fruit is a crucial quality feature, and the external coloration of most citrus fruits is due to the accumulation of carotenoids. The molecular regulation of carotenoid biosynthesis and accumulation in pericarp is limited due to the lack of mutant. Structural genes of the carotenoid biosynthesis pathway have been isolated and characterized [14,15,16,17,18]. The plant hormone ABA is an end product of the carotenoid biosynthetic pathway generated by the enzymatic cleavage of 9-cis-epoxycarotenoid dioxygenase (NCEDs). Due to the importance of carotenoids, many efforts have been made to understand the molecular basis of the regulation of carotenoid biosynthesis and accumulation
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