Manipulation of ZDS in tomato exposes carotenoid- and ABA-specific effects on fruit development and ripening.

Ryan P Mcquinn,Amanda G Gray,Nigel E Gapper,Alisdair R Fernie,Silin Zhong,James J Giovannoni,Zhangjun Fei,Takayuki Tohge

doi:10.1111/pbi.13377

Abstract

SummarySpontaneous mutations in fruit‐specific carotenoid biosynthetic genes of tomato (Solanum lycopersicum) have led to improved understanding of ripening‐associated carotenogenesis. Here, we confirm that ZDS is encoded by a single gene in tomato transcriptionally regulated by ripening transcription factors RIN, NOR and ethylene. Manipulation of ZDS was achieved through transgenic repression and heterologous over‐expression in tomato. CaMV 35S‐driven RNAi repression inhibited carotenoid biosynthesis in all aerial tissues examined resulting in elevated levels of ζ‐carotene isomers and upstream carotenoids, while downstream all trans‐lycopene and subsequent photoprotective carotenes and xanthophylls were diminished. Consequently, immature fruit displayed photo‐bleaching consistent with reduced levels of the photoprotective carotenes and developmental phenotypes related to a reduction in the carotenoid‐derived phytohormone abscisic acid (ABA). ZDS‐repressed ripe fruit was devoid of the characteristic red carotenoid, all trans‐lycopene and displayed brilliant yellow pigmentation due to elevated 9,9′ di‐cis‐ζ‐carotene. Over‐expression of the Arabidopsis thaliana ZDS (AtZDS) gene bypassed endogenous co‐suppression and revealed ZDS as an additional bottleneck in ripening‐associated carotenogenesis of tomato. Quantitation of carotenoids in addition to multiple ripening parameters in ZDS‐altered lines and ABA‐deficient fruit‐specific carotenoid mutants was used to separate phenotypic consequences of ABA from other effects of ZDS manipulation and reveal a unique and dynamic ζ‐carotene isomer profile in ripe fruit.

Highlights

Carotenoids play pivotal roles throughout plant development, among the most observable being coloration of ripe fruit and flowers for attraction of seed dispersing frugivores and pollinators
Given the limited knowledge of ZDS in terms of its regulation and phenotypic consequences on fruit development and ripening, we explored the consequences of transgenic manipulation of ZDS throughout tomato fruit development, investigating its function via RNAi-guided repression and over-expression using a heterologous gene from Arabidopsis (AtZDS)
Multiple steps of carotenoid biosynthesis are represented by multigene families (e.g. Solanum lycopersicum PSY1; SlPSY2; SlPSY3, and SlLCY-B/ CRTL-B1; SlBCYC/ CRTL-B2; Table S1), the origins of which can be traced in some cases to a whole-genome triplication event Tomato Genomics Consortium (TGC, 2012)

Summary

Introduction

Carotenoids play pivotal roles throughout plant development, among the most observable being coloration of ripe fruit and flowers for attraction of seed dispersing frugivores and pollinators. Duplication of genes in a majority of biosynthetic steps in tomato illuminated chloroplast- and chromoplast-specific pathways clarifying ripening-associated carotenogenesis (Galpaz et al, 2006; Sato et al, 2012; Figure S1 and Table S1). Natural mutations in genes involved in chromoplast-specific carotenogenesis (e.g. r, PSY1; tangerine, CRTISO; Beta, CYC-B/CRTL-B2) have allowed researchers to functionally define many steps of the pathway relevant to fruit ripening (Fray and Grierson, 1993; Isaacson et al, 2002; Ronen et al, 2000) and led to some of the colour variation in tomato (yellow and orange fruit varieties) appreciated by consumers. The lack of gene duplication within the poly-cis-transformation of 15-cisphytoene to all trans-lycopene limits the assessment of ripening roles for these genes

Results

Discussion

Conclusion