Characterizing the involvement of FaMADS9 in the regulation of strawberry fruit receptacle development

FaMADS9 is the strawberry (Fragaria x ananassa) gene exhibiting the highest homology to the tomato (Solanum lycopersicum) RIN gene. Transgenic lines were obtained in which FaMADS9 was silenced. The fruits of these lines did not show differences in basic parameters as fruit firmness or color, but exhibited lower Brix values in three of the four independent lines. The gene ontology MapMan category most enriched amongst the differentially expressed genes in the receptacle at the white stage corresponded to the regulation of transcription, including a high percentage of transcription factors and regulatory proteins associated with auxin action. In contrast, the most enriched categories at the red stage were: transport, lipid metabolism, and cell wall. Metabolomic analysis of the receptacle of the transformed fruits identified significant changes in the content of maltose, galactonic acid-1,4-lactone, proanthocyanidins and flavonols at the green/white stage, while isomaltose, anthocyanins and cuticular wax metabolisms were the most affected at the red stage. Among the regulatory genes differentially expressed in the transgenic receptacle are included several genes previously related to flavonoids metabolism such as MYB10, DIV, ZFN1, ZFN2, GT2, GT5, or associated to the action of hormones such as abscisic acid, SHP, ASR, GTE7 and SnRK2.7. The inference of a gene regulatory network, based on a Dynamic Bayesian approach, among the genes differentially expressed in the transgenic receptacle at the white and red stages, identified the genes KAN1, DIV, ZFN2 and GTE7 as putative targets of FaMADS9. A MADS9-specific CArG box is identified in the promoters of these genes.