Role of abscisic acid metabolism in regulation of bilberry fruit ripening
Authors
Katja Karppinen (presenting author) [1]
Amos Samkumar [1, 2]
Muhammad Furqan Ashraf [1]
Laura Jaakola [1, 3]
Keywords
Vaccinium; fruit ripening; abscisic acid; anthocyanins; carotenoids; light quality
Abstract
Fruit ripening is a complex developmental process involving metabolic and textural changes. Fruit ripening processes are controlled by plant hormones, most importantly ethylene and abscisic acid (ABA), but also affected by environmental factors such as light. Our investigations have focused on hormonal and environmental regulation of fruit ripening and anthocyanin biosynthesis in bilberry (Vaccinium myrtillus L.), an economically important wild berry species of the Northern Europe. Bilberries are rich source of health-beneficial anthocyanins which accumulate in berries during ripening. Our studies have shown that ABA level increases at the onset of bilberry fruit ripening preceding anthocyanin accumulation. Although both anthocyanin and carotenoid biosynthesis are upregulated during ripening, only anthocyanin levels increase. This inconsistency is due to simultaneous upregulation of carotenoid cleavage genes, leading to formation of apocarotenoids such as ABA. ABA treatment was shown to induce anthocyanin accumulation and upregulate fruit softening genes, suggesting that ABA plays an important role in the regulation of ripening in bilberry fruit. Light intensity is known to increase anthocyanin accumulation, and we have shown that intense white light given to unripe fruits upregulated the expression of the carotenoid biosynthetic and cleavage genes, indicating that light regulates anthocyanin biosynthesis through ABA metabolism. Also red light increased anthocyanin accumulation and transcriptional studies indicated signaling through ABA metabolism. In addition to anthocyanin biosynthesis, red light elevated expression of fruit softening genes, including pectate lyases (PLs), which have major role in depolymerization of cell wall pectin. Although blue light enhanced anthocyanin accumulation and PL expression, transcriptional studies found this regulation to be less associated with ABA signaling compared to red light, indicating involvement of another signaling route.
Funding
No funding information was provided in the submission.