Carotenoid biosynthesis and sequestration in red chilli pepper and its impact on colour intensity traits

Carotenoids are responsible for the red coloration of Capsicum annuum fruit; an important quality trait in chilli pepper. In order to characterise carotenoid formation in chilli, a discovery panel of C. Annuum genotypes with a range of red colour intensities has been analysed. The data indicated that colour intensity correlated with the amount of capsanthin and its esters, as well as transcript levels of the 1-deoxy-D-xyulose 5-phosphate synthase and phytoene synthase-1 (PSY-1) genes. Quantification of carotenoids through development and ripening revealed the presence of separate biosynthesis and accumulation phases. Subplastid fractionation demonstrated the differential sequestration of pigments in high and low intensity lines. Carotenoid accumulation was associated with the esterification of xanthophylls, expression of a carotenoid acyl transferase, and increased fibril content within the plastid. Interrogation of TEM images and carotenoid analysis of subplastid fractions suggest that the globular plastoglobuli are likely to be the progenitor of the characteristic fibrillar plastoglobuli found in pepper fruit. Collectively, these data provide an insight into the underpinning molecular, biochemical and cellular mechanisms associated with the synthesis and sequestration of carotenoids in chromoplast containing fruits, in addition to providing potential tools and resources for the breeding of high red colour intensity pepper varieties.