AtPDS overexpression in tomato: exposing unique patterns of carotenoid self-regulation and an alternative strategy for the enhancement of fruit carotenoid content
First author:Ryan P. McQuinn; Affiliations: Cornell University(康奈尔大学): Ithaca, USA
Corresponding author:James J. Giovannoni
The regulation of plant carotenogenesis (类胡萝卜素合成) is an active research area for both biological discovery and practical implementation (实践应用). In tomato (Solanum lycopersicum; 番茄), we demonstrate additional bottlenecks (瓶颈) exist in the poly-cis-transformation (聚顺变换) of phytoene (八氢番茄红素) to lycopene (番茄红素) in the context of ripening-induced PSY1 expression and activity and reveal phytoene desaturase (PDS; 八氢番茄红素脱氢酶), as a target for manipulation towards elevated lycopene content in maturing tomato fruit. Overexpression of Arabidopsis PDS, AtPDS, elevated PDS transcript abundance in all aerial tissues (地上部分组织) resulting in both altered carotenoid (类胡萝卜素) accumulation and associated pathway gene expression in a tissue-specific manner. Significant increases in downstream carotenoids (all-trans-lycopene and β-carotene) and minimal changes in carotenogenic gene expression (carotenoid isomerase-like 1, CRTIL1; 类胡萝卜素异构酶) suggest overexpression of heterologous (异源) AtPDS in tomato circumvents (绕过; 回避) endogenous regulatory mechanism observed with previous strategies. In transgenic leaves, depletion (用尽) of the PDS substrate, phytoene, was accompanied by minor, but significant increases in xanthophyll (叶黄素) production. Alterations in the leaf carotenogenic transcript profile, including the upstream MEP pathway, were observed revealing unique feedback and feedforward regulatory mechanisms in response to AtPDS overexpression. AtPDS overexpression in the background of the tangerine (carotenoid isomerase, CRTISO) mutant exposes its potential in elevating downstream cis-lycopene accumulation in ripe (成熟的) tomato fruit, as cis-lycopene is more bioavailable (生物可利用的) yet less abundant than all-trans-lycopene in the wild-type control. In summary, we demonstrate the limitation of PDS in ripening fruit, its utility (功用) in modifying carotenoid profiles towards improved quality, and reveal novel carotenoid pathway feedback regulation.
