Elucidating the Molecular Mechanisms Underpinning a Novel Acyanic Trait in Apple

Anthocyanin pigments are the major contributing molecules for colour development in apple fruit. Red, bicolour and blushed apples all accumulate anthocyanins to varying degrees, while green fruited varieties are show no anthocyanin accumulation in the fruit at harvest. While important for consumer-linked traits, these pigments are also bioactive and have numerous important physiological and ecological functions in plants, such as attraction of pollinators and seed dispersers, protection from high light irradiation, and scavenging free radicals produced in cells during stress conditions. We have identified a novel absence of anthocyanin (acyanic) trait in apple, which shows no anthocyanin formation in all tissue types and developmental stages. The underlying gene for this trait (‘a’) was mapped in multiple cross populations and shown to be recessive in its inheritance for loss of function for anthocyanin accumulation. Making use of SSR markers we were able to successfully identify a 3.4MB region of the genome as the location of a and identify an important international apple variety as a carrier of a. Genome analysis and annotation of the identified genomic region followed by gene expression analysis and pigment profiling via HPLC identified a candidate gene for a. Finally, DNA sequencing of the genomic context of this gene identified an hAT transposable element present in the coding sequence of a in acyanic plants. This transposon could be directly attributed to the disruption of the normal functioning of this gene and the resultant acanyic phenotype.

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