ENDOPOLYGALACTURONASE GENOTYPIC VARIATION IN PRUNUS

Abstract

Softening is an integral component of ripening for most fruit. The cell wall-metabolizing enzyme, endopolygalacturonase (endoPG), is involved in fruit softening of many species. In peach and nectarine (Prunus persica), maximum expression of endoPG coincides with the climacteric peak and period of rapid softening known as the melting phase that is characteristic of most fresh-market cultivars. We previously identified endoPG as the gene controlling the major fruit firmness and texture traits of Melting flesh (M) and Freestone (F) in peach. There appear to be at least two copies of the gene at the same locus, and we hypothesize that one copy controls M and another F, where the three main phenotypes observed are due to major deletions in one or both gene copies. Smaller changes in endoPG are suspected to result in quantitative differences in fruit firmness and texture. Other Prunus fruit crops, such as apricot, plum, and cherry, also have traits resembling M and F, and given the close synteny within Prunus, endoPG may play an important role in fruit quality in each of these crops. Therefore, diverse germplasm was surveyed with PCR tests for endoPG to confirm the role in Prunus fruit softening, and to identify further alleles in cultivated and related wild species that may convey useful new quality characteristics. A microsatellite associated with endoPG was the most polymorphic region of the gene using PCR amplification, allowing a detailed examination of endoPG genotypic diversity in Prunus. Sequence analysis of other parts of the gene is complementing our insights into the diversity and function of this important fruit quality gene.