Metabolic and transcriptional elucidation of the carotenoid biosynthesis pathway in peel and flesh tissue of loquat fruit during on-tree development

Abstract

BackgroundCarotenoids are the main colouring substances found in orange-fleshed loquat fruits. The aim of this study was to unravel the carotenoid biosynthetic pathway of loquat fruit (cv. ‘Obusa’) in peel and flesh tissue during distinct on-tree developmental stages through a targeted analytical and molecular approach.ResultsSubstantial changes regarding colour parameters, both between peel and flesh and among the different developmental stages, were monitored, concomitant with a significant increment in carotenoid content. Key genes and individual compounds that are implicated in the carotenoid biosynthetic pathway were further dissected with the employment of molecular (RT-qPCR) and advanced analytical techniques (LC-MS). Results revealed significant differences in carotenoid composition between peel and flesh. Thirty-two carotenoids were found in the peel, while only eighteen carotenoids were identified in the flesh. Trans-lutein and trans-β-carotene were the major carotenoids in the peel; the content of the former decreased with the progress of ripening, while the latter registered a 7.2-fold increase. However, carotenoid profiling of loquat flesh indicated trans-β-cryptoxanthin, followed by trans-β-carotene and 5,8-epoxy-β-carotene to be the most predominant carotenoids. High amounts of trans-β-carotene in both tissues were supported by significant induction in a chromoplast-specific lycopene β-cyclase (CYCB) transcript levels. PSY1, ZDS, CYCB and BCH were up-regulated and CRTISO, LCYE, ECH and VDE were down-regulated in most of the developmental stages compared with the immature stage in both peel and flesh tissue. Overall, differential regulation of expression levels with the progress of on-tree fruit development was more evident in the middle and downstream genes of carotenoid biosynthetic pathway.ConclusionsCarotenoid composition is greatly affected during on-tree loquat development with striking differences between peel and flesh tissue. A link between gene up- or down-regulation during the developmental stages of the loquat fruit, and how their expression affects carotenoid content per tissue (peel or flesh) was established.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-017-1041-3) contains supplementary material, which is available to authorized users.

Expression of a Chromoplast-Specific Lycopene β-Cyclase Gene (CYC-B) Is Implicated in Carotenoid Accumulation and Coloration in the Loquat

“…In this study, the transcription levels of the CYC-B gene exhibited significant upregulation at the majority of developmental stages of yellow and white-fleshed loquats, as previously reported by Hadjipieri et al [37]. At the FM stage, the expression of CYC-B gene was downregulated except in the pulp of 'Dawuxing'.…”

Molecular Cloning and Characterization of Carotenoid Pathway Genes and Carotenoid Content in Ixeris dentata var. albiflora

“…In this study, we identified seven crucial genes that are responsible for carotenoid biosynthesis pathway: phytoene synthase (PSY), phytoene desaturase (PDS), ξ-carotene desaturase (ZDS), lycopene β-cyclase (LCYB), β-ring carotene hydroxylase (CHXB), ε-ring carotene hydroxylase (CHXE), and zeaxanthin epoxidase (ZEP). PSY is the initial and crucial enzyme in this pathway that helps to generate phytoene, from 2 geranylgeranyl diphosphate (GGDP) molecule condensation [ 16 ]. PDS helps to convert phytoene in to ξ-carotene and it further turns into lycopene in the presence of ZDS.…”

Metabolomic Profiling of Carotenoid Constituents in Physalis peruviana During Different Growth Stages by LC‐MS/MS Technology

“…The changes in the lutein level along the fruit development time course were reasonable, as lutein and zeaxanthin can be interconverted in the plant through the intermediate meso‐zeaxanthin (Prado‐Cabrero et al., ). In addition, the rapid decline in the lutein level at the full‐ripe stage can be linked to the significant down‐regulation of lycopene β‐cyclase and lycopene ε‐cyclase expression levels during this stage (Hadjipieri et al., ).…”