Single gene mutations affecting the biosynthesis of anthocyanins in various raspberry fruits

Fruit pigmentation in raspberries (Rubus idaeus L., Rosaceae) is considered to be a complex trait involving not only the amount but also type of various pigments and co-pigments where a range of color patterns from deep purple to yellow exists (1). Therefore, a better understanding of genetic control and regulation of anthocyanin formation in raspberry and fruit ripening process is needed to accomplish an important association between beneficial compounds and their positive effects on human health. Various colored raspberries contain different concentrations of phenolic metabolites, however, block of a certain class of compounds was not observed except anthocyanins (2). However, there are no clear explanations about the genetic control and their regulation process during fruit development in raspberry. Thus, non-red raspberries offer an opportunity to study and explore the reason behind the loss of red pigments, the anthocyanins, in yellow and orange raspberry fruits. The current study provides important details and new insights in view of exploring the genetic mechanism controlling the biosynthesis of important fruit pigments. The in-silico search of an available Rubus “Heritage” genome draft with Ans of Fragaria x ananassa as template enabled the assembly of a putative Ans gene of Rubus. Further, molecular cloning of Ans gene from various colored raspberries revealed various type of mutations (RAMT-1 to RAMT-6) leading to truncated proteins in various yellow and orange fruiting raspberries, which lack conserved regions for substrate, cosubstrate and iron binding sites. The complementation of ´KO´ line of Arabidopsis via Ans gene from “Tualmeen” elaborates the functional role of this gene in the anthocyanin biosynthesis pathway in raspberry as compared to mutated Ans gene from one of the yellow fruiting “Anne” with truncated ANS protein. Therefore, it is suggested that all these non-red raspberry genotypes might have originated from a mutation event in the Ans gene from different ancestors. The findings of current study conclude that fruit-specific mutations in the anthocyanin pathway have led to the loss of anthocyanins and produce yellow and also orange pigmented raspberry fruits. In case of reduced anthocyanins, carotenoids are considered to be the main pigments accounting for the fruit color in raspberries