Gene expression of DAM5 and DAM6 is suppressed by chilling temperatures and inversely correlated with bud break rate.

We previously identified a cluster of d ormancy-a ssociated M ADS-box transcription factors (DAM genes) in peach [Prunus persica (L.) Batsch] as potential candidates for control of the non-dormant phenotype observed in the evg mutant. Of these genes, DAM3, DAM5 and DAM6 were winter expressed, suggesting a role for these genes during endodormancy. We used peach cultivars with contrasting chilling requirements (CR) for bud break to observe the expression of DAM3, DAM5 and DAM6 in response to chilling accumulation in the field and controlled environments. Vegetative terminal and floral buds were sampled weekly from field grown 'Contender' (1050 h CR), 'Rubyprince' (850 h CR) and 'Springprince' (650 h CR) peach cultivars through winter 2008-2009. Flower and vegetative terminal bud break potential was evaluated at each sampling by forcing cuttings in a growth-permissive environment. We also measured vegetative terminal bud break and DAM gene expression in potted 'Contender' and 'Peen-To' (450 h CR) trees under controlled-environment cold exposure. DAM3, DAM5 and DAM6 are all suppressed by exposure to chilling temperatures in the field and in controlled conditions. Expression of DAM5 and DAM6 are higher in high chill cultivars prior to chilling accumulation and their expression level reaches a minimum in each cultivar coincident with acquisition of bud break competence. Expression levels of DAM5 and DAM6 in vegetative tips in controlled environment conditions were negatively correlated with the time required for bud break in forcing conditions. The expression patterns of DAM5 and DAM6 are consistent with a role as quantitative repressors of bud break.

A deletion affecting several gene candidates is present in the Evergrowing peach mutant.

Evergrowing (EVG) peach is one of only two described mutants affecting winter dormancy in woody perennial species. EVG peach does not set terminal buds, cease new leaf growth, nor enter into a dormant resting phase in response to winter conditions. The EVG mutation segregates in F2 progeny as a single recessive nuclear gene. A local molecular genetic linkage map around EVG was previously developed using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers, and a bacterial artificial chromosome (BAC) contig that contains the EVG mutation was assembled. A MADS box coding open reading frame (ORF) was found in a BAC of this contig and used as a probe. The probe detected a polymorphism between the wild-type and mutant genomes, and the polymorphism is indicative of a deletion in EVG peach. The EVG gene region contained six potential MADS-box transcription factor sequences, and the deletion in EVG affected at least four of these. The deletion was bracketed using RFLP analysis, which showed that it is contained within a segment of the genome no greater than 180 kb.