Transcriptional analysis in high-anthocyanin tomatoes reveals synergistic effect of Aft and atv genes

Anthocyanins are high value plant antioxidants, which are not present in the fruits of the cultivated tomato. However, both the dominant gene Anthocyanin fruit (Aft) and the recessive gene atroviolacea (atv), when introgressed into the domesticated tomato from two different wild Solanum species, stimulate a limited anthocyanin pigmentation. Surprisingly, the double mutant Aft/Aft atv/atv gives rise to intensely purple pigmented tomatoes. A transcript profiling analysis was carried out using quantitative RT-PCR and GeneChip® Tomato Genome Arrays to identify differentially expressed genes when comparing Ailsa Craig, Aft/Aft, atv/atv, and Aft/Aft atv/atv fruits. Anthocyanin levels and the expression of the genes involved in anthocyanin production and compartmentalization were higher in the peel of Aft/Aft atv/atv fruits than in the individual parental lines. Moreover, a synergistic effect of the two alleles Aft and atv on the transcription of specific anthocyanin genes and the activation of the whole anthocyanin pathway was observed. Among the differentially expressed transcripts, genes involved in the phenylpropanoid pathway, biotic and abiotic stress responses, cell wall and hormone metabolism were over-represented in Aft/Aft atv/atv fruit peel. Transcriptomic analyses thus revealed that the activation of anthocyanin synthesis in the peel of tomato fruit was accompanied by a complex remodulation of gene expression.