Carotenoid responses to environmental stimuli: Integrating redox and carbon controls into a fruit model

Abstract

Carotenoids play an important role in plant adaptation to fluctuating environments as well as in the human diet by contributing to the prevention of chronic diseases. Insights have been gained recently into the way individual factors, genetic, environmental or developmental, control the carotenoid biosynthetic pathway at the molecular level. The identification of the rate-limiting steps of carotenogenesis has paved the way for programmes of breeding, and metabolic engineering, aimed at increasing the concentration of carotenoids in different crop species. However, the complexity that arises from the interactions between the different factors as well as from the coordination between organs remains poorly understood. This review focuses on recent advances in carotenoid responses to environmental stimuli and discusses how the interactions between the modulation factors and between organs affect carotenoid build-up. We develop the idea that reactive oxygen species/redox status and sugars/carbon status can be considered as integrated factors that account for most effects of the major environmental factors influencing carotenoid biosynthesis. The discussion highlights the concept of carotenoids or carotenoid-derivatives as stress signals that may be involved in feedback controls. We propose a conceptual model of the effects of environmental and developmental factors on carotenoid build-up in fruits. This review presents an assessment of the current understanding of how the different environmental factors and their interactions influence carotenoid accumulation at the organ level. We develop the idea that environmental factors converge to modulate reactive oxygen species (ROS)/redox status (influenced by oxidative stress), and sugars/carbon status (which results from the balance between carbon gains and losses, and allocation between competing organs) and in this way regulate carotenoid accumulation. The discussion highlights the concept of carotenoids or carotenoid-derivatives as stress signals that may be involved in feedback controls. We propose a conceptual model of the effects of environmental and developmental factors that accounts for the known roles played by ROS and sugars on carotenoid build-up in fruits. © 2013 John Wiley & Sons Ltd.