Abstract:
Carotenoids are lipophilic isoprenoid compounds responsible for yellow and orange pigmentation in fruits and vegetables. In plants, they protect the photosynthetic unit from photo-oxidative stress and are precursors to two phytohormones, abscisic acid, and strigolactones. Consumption of these secondary metabolites has been associated with reducing the risk of diseases like prostate cancer and age-related macular degeneration. Apple is one of the most significant fruit crops globally. The skin of the fruit accumulates high levels of anthocyanins and carotenoids. However, the flesh has low levels of carotenoids compared to the skin. Increasing carotenoids in the flesh of apple will increase its nutritional value as flesh occupies most of the fruit space. A cross between ‘Aotea’ cultivar (small fruit with high carotenoids and yellow flesh) and ‘Malling 9’ (large fruit with low carotenoids and white flesh) yielded progenies with varying flesh colour and carotenoid levels. The population was utilized to understand the genetic control of carotenoid biosynthesis in apple flesh. Single nucleotide polymorphism (SNP) genotyping was conducted to identify the segregating alleles of carotenoid biosynthesis pathway genes from ‘Aotea’ in the population. Candidate genes were selected based on the allelic analysis, regression analysis, and published literature. Expression analysis of the candidate gene isopentenyl pyrophosphate (IPPI) in yellow and white-fleshed cultivars revealed high expression at an early stage of fruit development, which may influence carotenoid concentration in the flesh. Functional analysis revealed the potential role of phytoene synthase 4 (PSY4) in regulating the first committed step of the carotenoid biosynthesis pathway in yellow-fleshed cultivars. These findings provide insights into understanding the carotenoid biosynthesis pathway in the flesh of yellow apple cultivars in order to increase the carotenoid concentration in commercial cultivars, and thereby increasing fruit nutritional value.