Silencing of strawberry pathogen defence related candidate genes by using specific strawberry fruit ripening-related promoters: an intragenic approach to improve fruit quality and resistance

Improving fruit quality and resistance to pathogens in strawberry by friendly biotechnological approaches represents a major issue to reduce the use of chemicals and pesticides and an important goal for breeding. We have designed new RNAi intragenic silencing constructions by combining specific strawberry promoters and pathogen defence-related candidate genes to silence endogenous target genes in a fruit ripening related manner thus avoiding any unwanted effect on plant growth and development. For this, a ~3000-bp DNA fragment upstream FvDOF2 and FvFAAT2 coding regions was fused to RNAi designed cassettes for FaWRKY1 and FaNPR3.1 genes. Four different binary plasmid constructions were generated using pMinMYB as a recipient plasmid frame carrying the MdMYB10 gene from a red-fleshed apple as natural selectable marker. The fruit-specific transcription factor FvDOF2 regulates the production of volatile eugenol in ripe fruit receptacles whereas gene FvAAT2 encodes a fruit-related acyltransferase involved in strawberry aroma biogenesis. Also, FaWRKY1 transcription factor negatively regulates resistance to Colletotrichum acutatum in fruit upon infection and FaNPR3.1 is the strawberry orthologue of the Arabidopsis AtNPR3/AtNPR4 salicylic acid (SA) receptors acting as transcriptional co-repressors in plant immunity. Using these plasmid constructs, stable red transformant intragenic strawberry lines silencing target genes are being produced and will be tested for increase resistance to different pathogens.