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Distinct Mechanisms of the ORANGE Protein in Controlling Carotenoid Flux.

Abstract：

:β-Carotene adds nutritious value and determines the color of many fruits, including melon (Cucumis melo). In melon mesocarp, β-carotene accumulation is governed by the Orange gene (CmOr) golden single-nucleotide polymorphism (SNP) through a yet to be discovered mechanism. In Arabidopsis (Arabidopsis thaliana), OR increases carotenoid levels by posttranscriptionally regulating phytoene synthase (PSY). Here, we identified a CmOr nonsense mutation (Cmor-lowβ) that lowered fruit β-carotene levels with impaired chromoplast biogenesis. Cmor-lowβ exerted a minimal effect on PSY transcripts but dramatically decreased PSY protein levels and enzymatic activity, leading to reduced carotenoid metabolic flux and accumulation. However, the golden SNP was discovered to not affect PSY protein levels and carotenoid metabolic flux in melon fruit, as shown by carotenoid and immunoblot analyses of selected melon genotypes and by using chemical pathway inhibitors. The high β-carotene accumulation in golden SNP melons was found to be due to a reduced further metabolism of β-carotene. This was revealed by genetic studies with double mutants including carotenoid isomerase (yofi), a carotenoid-isomerase nonsense mutant, which arrests the turnover of prolycopene. The yofi F2 segregants accumulated prolycopene independently of the golden SNP Moreover, Cmor-lowβ was found to inhibit chromoplast formation and chloroplast disintegration in fruits from 30 d after anthesis until ripening, suggesting that CmOr regulates the chloroplast-to-chromoplast transition. Taken together, our results demonstrate that CmOr is required to achieve PSY protein levels to maintain carotenoid biosynthesis metabolic flux but that the mechanism of the CmOr golden SNP involves an inhibited metabolism downstream of β-carotene to dramatically affect both carotenoid content and plastid fate.

journal_name

Plant Physiol

journal_title

Plant physiology

authors

Chayut N,Yuan H,Ohali S,Meir A,Sa'ar U,Tzuri G,Zheng Y,Mazourek M,Gepstein S,Zhou X,Portnoy V,Lewinsohn E,Schaffer AA,Katzir N,Fei Z,Welsch R,Li L,Burger J,Tadmor Y

doi

10.1104/pp.16.01256

subject

Has Abstract

pub_date

2017-01-01 00:00:00

pages

376-389

issue

eissn

0032-0889

issn

1532-2548

pii

pp.16.01256

journal_volume

173

pub_type

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Distinct Mechanisms of the ORANGE Protein in Controlling Carotenoid Flux.