Phenotypes of the tomato (Solanum lycopersicum) high pigment-2dg (hp-2dg) and hp-2j mutants are caused by lesions in the gene encoding DEETIOLATED1, a negative regulator of light signaling. Homozygous hp-2dg and hp-2j plants display a plethora of distinctive developmental and metabolic phenotypes in comparison to their normal isogenic counterparts. These mutants are, however, best known for the increased levels of carotenoids, primarily lycopene, and other plastid-accumulating functional metabolites. In this study we analyzed the transcriptional alterations in mature-green, breaker, and early red fruits of hp-2dg/hp-2dg plants in relation to their normal counterparts using microarray technology. Results show that a large portion of the genes that are affected by hp-2dg mutation display a tendency for up- rather than down-regulation. Ontology assignment of these differentially regulated transcripts revealed a consistent up-regulation of transcripts related to chloroplast biogenesis and photosynthesis in hp-2dg mutants throughout fruit ripening. A tendency of up-regulation was also observed in structural genes involved in phytonutrient biosynthesis. However, this up-regulation was not as consistent, positioning plastid biogenesis as an important determinant of phytonutrient overproduction in hp-2dg and possibly other hp mutant fruits. Microscopic observations revealed a highly significant increase in chloroplast size and number in pericarp cells of mature-green hp-2dg/hp-2dg and hp-2j/hp-2j fruits in comparison to their normal counterparts. This increase could be observed from early stages of fruit development. Therefore, the molecular trigger that drives phytonutrient overproduction in hp-2dg and hp-2j mutant fruits should be initially traced at these early stages.

Tomato yellow leaf curl virus (TYLCV) is a devastating disease of tomato (Solanum lycopersicum) that can be effectively controlled by the deployment of resistant cultivars. The TYLCV-resistant line TY172 carries a major recessive locus for TYLCV resistance, designated ty-5, on chromosome 4. In this study, the association between 27 polymorphic DNA markers, spanning the ty-5 locus, and the resistance characteristics of individual plants inoculated with TYLCV in 51 segregating recombinant populations were analyzed. These analyses localized ty-5 into a 425 bp region containing two transversions: one in the first exon of a gene encoding the tomato homolog of the messenger RNA surveillance factor Pelota (Pelo), and a second in its proximal promoter. Analyses of susceptible and resistant lines revealed that the relative transcript level of the gene remained unchanged, regardless of whether the plants were infected with TYLCV or not. This suggests that the polymorphism discovered in the coding region of the gene controls the resistance. Silencing of Pelo in a susceptible line rendered the transgenic plants highly resistant, while in the resistant line TY172 had no effect on symptom development. In addition, over-expression of the susceptible allele of the gene in the resistant TY172 line rendered it susceptible, while over-expression of the resistant allele in susceptible plants had no effect. These results confirm that Pelo is the gene controlling resistance at the ty-5 locus. Pelo, implicated in the ribosome recycling-phase of protein synthesis, offers an alternative route to promote resistance to TYLCV and other viruses. Tomato is one of the most important food crops worldwide, providing phytonutrients and color to our diet. Tomato yellow leaf curl virus (TYLCV) is one of the most devastating viruses of cultivated tomatoes and a key limiting factor to tomato production in major tomato-growing areas. The management of TYLCV is difficult because its whitefly vector populations can reach high numbers and relies heavily on the application of hazardous chemicals (insecticides). Breeding TYLCV-resistant tomato cultivars provides an attractive, environmentally friendly strategy to reduce yield losses caused by the virus. Considerable efforts have been invested in breeding TYLCV-resistant tomato cultivars. The discovery and utilization of genes controlling resistance can expedite the breeding process and highlight innate means to promote such resistance. Here we report the discovery of the gene controlling TYLCV resistance at the ty-5 locus. It was found that the messenger RNA surveillance factor Pelo is responsible for this resistance. Our discovery, together with the recent discovery of the gene controlling resistance at the Ty-1/Ty-3 locus, can lead to precision pyramiding of these two genes to enhance the spectrum of resistance of tomato plants to TYLCV, and possibly to other begomoviruses.