Extensive transcriptomic studies on the roles played by abscisic acid and auxins in the development and ripening of strawberry fruits

Strawberry is an ideal model for studying the molecular biology of the development and ripening of non-climacteric fruits. Hormonal regulation of gene expression along all these processes in strawberries is still to be fully elucidated. Although auxins and ABA have been pointed out as the major regulatory hormones, few high-throughput analyses have been carried out to date. The role for ethylene and gibberellins as regulatory hormones during the development and ripening of the strawberry fruit remain still elusive. By using a custom-made and high-quality oligo microarray platform done with over 32,000 probes including all of the genes actually described in the strawberry genome, we have analysed the expression of genes during the development and ripening in the receptacles of these fruits. We classify these genes into two major groups depending upon their temporal and developmental expression. First group are genes induced during the initial development stages. The second group encompasses genes induced during the final maturation and ripening processes. Each of these two groups has been also divided into four sub-groups according their pattern of hormonal regulation. By analyzing gene expression, we clearly show that auxins and ABA are the main and key hormones that combined or independently are responsible of the development and ripening process. Auxins are responsible for the receptacle fruit development and, at the same time¸ prevent ripening by repressing crucial genes. ABA regulates the expression of the vast majority of genes involved in the ripening. The main genes expressed under the control of these hormones are presented and their physiological rule discussed. We also conclude that ethylene and gibberellins do not seem to play a prominent role during these processes.