Abstract
Pummelo (Citrus maxima) is one of important fruit trees, which belongs to Citrus species. The fruits of different pummelo cultivars have different colors and differ in the contents of carotenoid. Our results clearly showed that ‘Huangjinmiyou’ (HJMY) has the highest content of β-carotene, followed by ‘Hongroumiyou’ (HRMY) and ‘Guanximiyou’ (GXMY). Lycopene is dominantly accumulated in HRMY. However, the molecular mechanism underlying the carotenoid accumulation in pummelo flesh is not fully understood. In this study, we used the RNA-Seq technique to investigate the candidate genes of carotenoid metabolism in the flesh of pummelo cv. GXMY and its mutants HRMY and HJMY in three development periods of fruit. After data assembly and bioinformatic analysis, a total of 357 genes involved in biosynthesis of secondary metabolites were isolated, of which 12 differentially expressed genes (DEGs) are involved in carotenoid biosynthesis. Among these 12 DEGs, phytoene synthase (PSY2), lycopene β-cyclase (LYCB2), lycopene Ɛ-cyclase (LYCE), carotenoid cleavage dioxygenases (CCD4), 9-cis-epoxycarotenoid dioxygenase (NCED2), aldehyde oxidase 3 (AAO3), and ABA 8′-hydroxylases (CYP707A1) are the most distinct DEGs in three pummelo cultivars. The co-expression analysis revealed that the expression patterns of several transcription factors such as bHLH, MYB, ERF, NAC and WRKY are highly correlated with DEGs, which are involved in carotenoid biosynthesis. In addition, the expression patterns of 22 DEGs were validated by real-time quantitative PCR (RT-qPCR) and the results are highly concordant with the RNA-Seq results. Our results provide a global vision of transcriptomic profile among three pummelo cultivars with different pulp colors. These results would be beneficial to further study the molecular mechanism of carotenoid accumulation in pummelo flesh and help the breeding of citrus with high carotenoid content.
Highlights
Carotenoid is the second most abundant compound in natural pigments and provides colorless, yellow, orange, and red colors for many fruits, flowers and vegetables [1]
HJMY has the highest content of β-carotene with a value of about 681.45 mg/kg fresh weight (FW), almost 34 times higher than that in GXMY and HRMY at an early development stage 40 days after flowering (DAF)
The β-carotene content decreases at 100 DAF and increases at 190 DAF in HJMY and HRMY, whereas it decreases during the entire development of GXMY
Summary
Carotenoid is the second most abundant compound in natural pigments and provides colorless, yellow, orange, and red colors for many fruits, flowers and vegetables [1]. It is clear that coloration of most citrus fruits is mainly caused by the accumulation of carotenoid [2,3,4]. In order to regulate coloration of citrus fruit genetically, several novel methods, such as gene cloning and transcriptomic and proteomic analysis, are used to isolate genes associated with carotenoid metabolism [2,6]. The carotenoid regulation mechanism in pummelo flesh was not well understood. It is helpful to identify genetic control of carotenoid metabolism with pummelo as materials. Pummelo, one of three basic species of citrus, shows lower heterozygosity than sweet orange, so it can overcome heterozygous loci in genetic analysis. “Feicui” by high-performance liquid chromatography (HPLC) and GC/MS and concluded that there are different tissue-biased patterns of carotenoid biosynthesis in pummelos with different flesh colors. There was no report on the molecular mechanism of carotenoid accumulation in pummelo flesh
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
