Abstract
The diverse fruit colors of peppers (Capsicum spp.) are due to variations in carotenoid composition and content. Mature fruit color in peppers is regulated by three independent loci, C1, C2, and Y. C2 and Y encode phytoene synthase (PSY1) and capsanthin-capsorubin synthase (CCS), respectively; however, the identity of the C1 gene has been unknown. With the aim of identifying C1, we analyzed two pepper accessions with different fruit colors: Capsicum frutescens AC08-045 and AC08-201, whose fruits are light yellow and white, respectively. Ultra-performance liquid chromatography showed that the total carotenoid content was six times higher in AC08-045 than in AC08-201 fruits, with similar composition of main carotenoids and slight difference in minor components. These results suggest that a genetic factor in AC08-201 may down-regulate overall carotenoid biosynthesis. Analyses of candidate genes related to carotenoid biosynthesis and plastid abundance revealed that both accessions carry non-functional alleles of CCS, golden2-like transcription factor (GLK2), and PSY1. However, a nonsense mutation (C2571T) in PRR2, a homolog of Arabidopsis pseudo response regulator2-like (APRR2), was present in only AC08-201. In a population derived from a cross between AC08-045 and AC08-201, a SNP marker based on the nonsense mutation co-segregated fully with fruit color, implying that the mutation in PRR2 may cause the white color of AC08-201 fruits. Transmission electron microscopy (TEM) of AC08-201 fruit pericarp also showed less developed granum structure in chloroplast and smaller plastoglobule in chromoplast compared to those of AC08-045. Virus-induced gene silencing (VIGS) of PRR2 significantly reduced carotenoid accumulation in Capsicum annuum ‘Micropep Yellow’, which carries non-functional mutations in both PSY1 and CCS. Furthermore, sequence analysis of PSY1, CCS, and PRR2 in other white pepper accessions of C. annuum and Capsicum chinense showed that they commonly have non-functional alleles in PSY1, CCS, and PRR2. Thus, our data demonstrate that the fruit color locus C1 in Capsicum spp. corresponds to the gene PRR2.
Highlights
Carotenoids, called tetraterpenoids, are derived from 8 isoprene units and contain 40 carbons in their polyene backbone
We showed that the white color of C. frutescens AC08201 is due to a nonsense mutation in pseudo response regulator2like (PRR2), as well as PSY1 and capsanthincapsorubin synthase (CCS) mutations
These results suggest that the color difference between the two accessions is due to their abundance rather than composition of carotenoids
Summary
Carotenoids, called tetraterpenoids, are derived from 8 isoprene units and contain 40 carbons in their polyene backbone. Carotenoids play crucial roles in plants, including photosynthesis and photoprotection, and provide precursors for the biosynthesis of phytohormones such as abscisic acid (ABA) and strigolactones (Domonkos et al, 2013; Nambara and Marion-Poll, 2005; Al-Babili and Bouwmeester, 2015). Whereas the red color in tomato is due to lycopene accumulation, the red color in peppers results from the accumulation of capsanthin and capsorubin (Paran and van der Knaap, 2007). This pepper-specific process is regulated by capsanthin-capsorubin synthase (CCS), which converts downstream products of lycopene, antheraxanthin and violaxanthin into capsanthin and capsorubin, respectively (Bouvier et al, 1994)
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