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Abstract Key messageA paralog ofCell Size Regulator(CSR),CSR-like1, underlies the novelfw6.2QTL in tomato. The gene and locus regulate fruit weight by increasing pericarp cell size and its function on fruit weight appears to be conserved in other crops. AbstractFruit weight is a quantitative trait that was under strong selection during the domestication of fruit and vegetable crops such as tomato (Solanum lycopersicum). While numerous fruit weight QTLs have been identified, only three tomato fruit weight genes have been cloned. In this study, we utilized a genetically diverse tomato panel, the Varitome collection, to identify additional genetic loci that control fruit weight. We mapped and fine mapped two fruit weight QTLs on chromosome 6,fw6.1andfw6.2, by using Genome Wide Association studies (GWAS) and linkage mapping in bi-parental populations. We identified a member of theCell Size Regulatorfamily,CSR-like1, as the likely candidate underlyingfw6.2. The near isogenic lines (NILs) carrying the derived allele offw6.2produced heavier fruits with larger fruit pericarp cells than lines with wildtype (WT) allele. Transgenic downregulation ofCSR-like1led to a decrease in fruit weight and pericarp cells, supporting the role of this gene at thefw6.2locus. The haplotype analysis implied that theCSR-like1-Derived (CSR-like1-D) allele was selected in the transition from the fully wildS. pimpinellifoliumto the earliestS. lycopersicum cerasiformeaccessions.Four single nucleotide polymorphisms (SNPs) were identified in the regulatory region ofCSR-like1that were conserved in the accessions carryingCSR-like1-WT and were significantly associated with lower fruit weight and pericarp cell size at the locus. Moreover, a pepper GWAS identified aCSR-like1ortholog that was associated with fruit weight. Together, our findings establishedCSR-like1as a novel fruit weight gene likely conserved in other crops in the Solanaceae family. 

Shape is a primary determinant of consumer preference for many horticultural crops and it is also associated with many aspects of marketing, harvest mechanics, and postharvest handling. Perceptions of quality and preference often map to specific shapes of fruits, tubers, leaves, flowers, roots, and other plant organs. As a result, humans have greatly expanded the palette of shapes available for horticultural crops, in many cases creating a series of market classes where particular shapes predominate. Crop wild relatives possess organs shaped by natural selection, while domesticated species possess organs shaped by human desires. Selection for visually-pleasing shapes in vegetable crops resulted from a number of opportunistic factors, including modification of supernumerary cambia, allelic variation at loci that control fundamental processes such as cell division, cell elongation, transposon-mediated variation, and partitioning of photosynthate. Genes that control cell division patterning may be universal shape regulators in horticultural crops, influencing the form of fruits, tubers, and grains in disparate species. Crop wild relatives are often considered less relevant for modern breeding efforts when it comes to characteristics such as shape, however this view may be unnecessarily limiting. Useful allelic variation in wild species may not have been examined or exploited with respect to shape modifications, and newly emergent information on key genes and proteins may provide additional opportunities to regulate the form and contour of vegetable crops.