No abstract

The APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) superfamily of transcriptional regulators is involved in several growth, development and stress responses processes in higher plants. Currently, the available information on the biological roles of AP2/ERF genes is derived from Arabidopsis thaliana. In the present work, we have investigated genomic and transcriptional aspects of AP2/ERF genes in the economically important perennial species, Malus × domestica. We have identified 259 sequences containing at least one ERF domain in apple genome. The vast majority of the putative proteins display predicted nuclear localization, compatible with a biological role in transcription regulation. The AP2 and ERF families are greatly expanded in apple. Whole-genome analyses in other plant species have identified a single genomic sequence with divergent ERF, whereas in apple seven soloists are present. In the apple genome, the most noteworthy expansion occurred in subgroups V, VIII and IX of the ERF family. Expression profiling analyses have revealed the association of ripening-involved ERF genes to scab (Venturia inequalis) pathogenesis in the susceptible Gala cultivar, indicating that gene expansion processes were accompanied by functional divergence. The presented analyses of AP2/ERF genes in apple provide evidences of shared ethylene-mediated signaling pathways in ripening and disease responses.

In order to investigate the genetic bases of the physiological syndrome mealiness that causes abnormal fruit softening and juice loss in apples, an integrative approach was devised, consisting of sensory, instrumental, biochemical, genetic, and genomic methods. High levels of activity of α-L-arabinofuranosidase (α-AFase), a hydrolase acting on the pectic component of the cell walls, were found in individuals exhibiting the mealiness phenotype in a segregating population. The expression levels of the previously uncharacterized apple AF gene MdAF3 are higher in fruits from plants consistently showing mealiness symptons and high α-AFase activity. The transcription of MdAF3 is differentially regulated in distinct genomic contexts and appears to be independent of ethylene. Thus, it is likely to be controlled by endogenous developmental mechanisms associated with fruit ripening. The use of integrative approaches has allowed the identification of a novel contributor to the mealiness phenotype in apple and it has been possible to overcome the problems posed by the unavailability of near-isogenic lines to dissect the genetic bases of a complex physiological trait in woody perennial species.

No abstract

No abstract