Looking for lost flavor in tomatoes: Commercially available tomatoes are renowned these days for sturdiness, but perhaps not for flavor. Heirloom varieties, on the other hand, maintain the richer flavors and sweeter tomatoes of years past. Tiemanet al.combined tasting panels with chemical and genomic analyses of nearly 400 varieties of tomatoes. They identified some of the flavorful components that have been lost over time. Identification of the genes that have also gone missing provides a path forward for reinstating flavor to commercially grown tomatoes.Science, this issue p.391

Fruits represent an important part of the human diet and show extensive variation in size and shape between and within cultivated species. The genetic basis of such variation has been studied most extensively in tomato, where currently six quantitative trait loci (QTLs) involving these traits have been fine-mapped and the genes underlying the QTLs identified. The genes responsible for the cloned QTLs belong to families with a few to many members. FASCIATED is encoded by a member of the YABBY family, CNR/FW2.2 by a member of the Cell Number Regulator family, SlKLUH/FW3.2 by a cytochrome P450 of the 78A class (CYP78A), LOCULE NUMBER by a member of the WOX family including WUSCHEL, OVATE by a member of the Ovate Family Proteins (OFP), and SUN by a member of the IQ domain family. A high portion of the history and current diversity in fruit morphology among tomato cultivars can be explained by modifications at four of these cloned QTLs. In melon, a number of QTLs involved in fruit morphology have been mapped, but the molecular basis for these QTLs is unknown. In the present review, we examine the current knowledge on the molecular basis of fruit morphology in tomato and transfer that information in order to define candidate genes of melon fruit shape and size QTLs. We hypothesize that different members of the gene families identified in tomato may have a role in the regulation of fruit morphology in other species. We anchored the published melon QTL map on the genome sequence and identified the melon family members of the six cloned tomato QTLs in the genome. We investigated the co-localization of melon fruit morphology QTLs and the candidate genes. We found that QTLs for fruit weight co-localized frequently with members of the CNR/FW2.2 and KLUH/FW3.2 families, as well as co-localizations between OFP family members and fruit-shape QTLs, making this family the most suitable to explain fruit shape variation among melon accessions.

Shapes of edible plant organs vary dramatically among and within crop plants. To explain and ultimately employ this variation towards crop improvement, we determined the genetic, molecular and cellular bases of fruit shape diversity in tomato. Through positional cloning, protein interaction studies, and genome editing, we report that OVATE Family Proteins and TONNEAU1 Recruiting Motif proteins regulate cell division patterns in ovary development to alter final fruit shape. The physical interactions between the members of these two families are necessary for dynamic relocalization of the protein complexes to different cellular compartments when expressed in tobacco leaf cells. Together with data from other domesticated crops and model plant species, the protein interaction studies provide possible mechanistic insights into the regulation of morphological variation in plants and a framework that may apply to organ growth in all plant species.

Background: A number of molecular marker linkage maps have been developed for melon (Cucumis melo L.) over the last two decades. However, these maps were constructed using different marker sets, thus, making comparative analysis among maps difficult. In order to solve this problem, a consensus genetic map in melon was constructed using primarily highly transferable anchor markers that have broad potential use for mapping, synteny, and comparative quantitative trait loci (QTL) analysis, increasing breeding effectiveness and efficiency via marker-assisted selection (MAS). Results: Under the framework of the International Cucurbit Genomics Initiative (ICuGI, http://www.icugi.org), an integrated genetic map has been constructed by merging data from eight independent mapping experiments using a genetically diverse array of parental lines. The consensus map spans 1150 cM across the 12 melon linkage groups and is composed of 1592 markers (640 SSRs, 330 SNPs, 252 AFLPs, 239 RFLPs, 89 RAPDs, 15 IMAs, 16 indels and 11 morphological traits) with a mean marker density of 0.72 cM/marker. One hundred and ninety-six of these markers (157 SSRs, 32 SNPs, 6 indels and 1 RAPD) were newly developed, mapped or provided by industry representatives as released markers, including 27 SNPs and 5 indels from genes involved in the organic acid metabolism and transport, and 58 EST-SSRs. Additionally, 85 of 822 SSR markers contributed by Syngenta Seeds were included in the integrated map. In addition, 370 QTL controlling 62 traits from 18 previously reported mapping experiments using genetically diverse parental genotypes were also integrated into the consensus map. Some QTL associated with economically important traits detected in separate studies mapped to similar genomic positions. For example, independently identified QTL controlling fruit shape were mapped on similar genomic positions, suggesting that such QTL are possibly responsible for the phenotypic variability observed for this trait in a broad array of melon germplasm. Conclusions: Even though relatively unsaturated genetic maps in a diverse set of melon market types have been published, the integrated saturated map presented herein should be considered the initial reference map for melon. Most of the mapped markers contained in the reference map are polymorphic in diverse collection of germplasm, and thus are potentially transferrable to a broad array of genetic experimentation (e.g., integration of physical and genetic maps, colinearity analysis, map-based gene cloning, epistasis dissection, and marker-assisted selection).

The present review aims to synthesize our present knowledge about the mechanisms implied in the biosynthesis of volatile compounds in the ripe tomato fruit, which have a key role in tomato flavour. The difficulties in identifiying not only genes or genomic regions but also individual target compounds for plant breeding are addressed. Ample variability in the levels of almost any volatile compound exists, not only in the populations derived from interspecific crosses but also in heirloom varieties and even in commercial hybrids. Quantitative trait loci (QTLs) for all tomato aroma volatiles have been identified in collections derived from both intraspecific and interspecific crosses with different wild tomato species and they (i) fail to co-localize with structural genes in the volatile biosynthetic pathways and (ii) reveal very little coincidence in the genomic regions characterized, indicating that there is ample opportunity to reinforce the levels of the volatiles of interest. Some of the identified genes may be useful as markers or as biotechnological tools to enhance tomato aroma. Current knowledge about the major volatile biosynthetic pathways in the fruit is summarized. Finally, and based on recent reports, it is stressed that conjugation to other metabolites such as sugars seems to play a key role in the modulation of volatile release, at least in some metabolic pathways.