Comprehending crystalline β-carotene accumulation by comparing engineered cell models and the natural carotenoid-rich system of citrus
Open Access
- 18 May 2012
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Experimental Botany
- Vol. 63 (12), 4403-4417
- https://doi.org/10.1093/jxb/ers115
Abstract
Genetic manipulation of carotenoid biosynthesis has become a recent focus for the alleviation of vitamin A deficiency. However, the genetically modified phenotypes often challenge the expectation, suggesting the incomplete comprehension of carotenogenesis. Here, embryogenic calli were engineered from four citrus genotypes as engineered cell models (ECMs) by over-expressing a bacterial phytoene synthase gene (CrtB). Ripe flavedos (the coloured outer layer of citrus fruits), which exhibit diverse natural carotenoid patterns, were offered as a comparative system to the ECMs. In the ECMs, carotenoid patterns showed diversity depending on the genotypes and produced additional carotenoids, such as lycopene, that were absent from the wild-type lines. Especially in the ECMs from dark-grown culture, there emerged a favoured β,β-pathway characterized by a striking accumulation of β-carotene, which was dramatically different from those in the wild-type calli and ripe flavedos. Unlike flavedos that contained a typical chromoplast development, the ECMs sequestered most carotenoids in the amyloplasts in crystal form, which led the amyloplast morphology to show a chromoplast-like profile. Transcriptional analysis revealed a markedly flavedo-specific expression of the β-carotene hydroxylase gene (HYD), which was suppressed in the calli. Co-expression of CrtB and HYD in the ECMs confirmed that HYD predominantly mediated the preferred carotenoid patterns between the ECMs and flavedos, and also revealed that the carotenoid crystals in the ECMs were mainly composed of β-carotene. In addition, a model is proposed to interpret the common appearance of a favoured β,β-pathway and the likelihood of carotenoid degradation potentially mediated by photo-oxidation and vacuolar phagocytosis in the ECMs is discussed.Keywords
This publication has 58 references indexed in Scilit:
- Regulation of carotenoid accumulation and the expression of carotenoid metabolic genes in citrus juice sacs in vitroJournal of Experimental Botany, 2011
- Screening and Selection of High Carotenoid Producing in Vitro Tomato Cell Culture Lines for [13C]-Carotenoid ProductionJournal of Agricultural and Food Chemistry, 2010
- Source to sink: regulation of carotenoid biosynthesis in plantsTrends in Plant Science, 2010
- Isolation and Characterization of the Z-ISO Gene Encoding a Missing Component of Carotenoid Biosynthesis in PlantsPlant Physiology, 2010
- Comparative proteomics of a lycopene‐accumulating mutant reveals the important role of oxidative stress on carotenogenesis in sweet orange (Citrus sinensis [L.] osbeck)Proteomics, 2009
- Metabolite Sorting of a Germplasm Collection Reveals the Hydroxylase3 Locus as a New Target for Maize Provitamin A BiofortificationPlant Physiology, 2009
- Molecular and functional characterization of a novel chromoplast-specific lycopene β-cyclase from Citrus and its relation to lycopene accumulationJournal of Experimental Botany, 2009
- Combinatorial genetic transformation generates a library of metabolic phenotypes for the carotenoid pathway in maizeProceedings of the National Academy of Sciences, 2008
- A novel bud mutation that confers abnormal patterns of lycopene accumulation in sweet orange fruit (Citrus sinensis L. Osbeck)Journal of Experimental Botany, 2007
- Sample extraction techniques for enhanced proteomic analysis of plant tissuesNature Protocols, 2006