| Tomato (Solanum lycopersicum) is a member of the large and phenotypically diverse Solanaceae family that includes several other agriculturally valuable crops such as potato, eggplant, pepper, petunia and tobacco. Along with its role as an important vegetable crop, tomato also serves as an excellent model system for studying fleshy fruit development. This dissertation focuses on the characterization of four tomato mutants: sticky peel (pe), uniform gray-green (ug), peach (p), and easy peel ( ep) that each display altered phenotypes associated with fruit development. The main research objectives were (1) to evaluate the phenotypes of these mutants (2) position each locus on the tomato genetic map and isolate the mutant genes by positional cloning and (3) functionally characterize the genes to determine their role in tomato fruit development.;Fruit of the pe mutant have sticky and glossy fruit surface and are cutin deficient with an altered wax profile. In addition, several phenotypes attributed to altered epidermal cell function are apparent in pe, including altered leaf cuticle composition, leading to increased transpiration, a lower trichome density and reduced anthocyanin accumulation. Genetic mapping revealed that pe encodes a new allele of CUTIN DEFICIENT 2 (CD2), a member of the Class IV homeodomain-leucine zipper transcription factor (TF) family that was previously only associated with a fruit-specific cuticle deficiency. The Arabidopsis anthocyaninless 2 mutant encodes a homolog of CD2 and additional characterization of this mutant revealed that it also exhibits a mildly cutin deficient phenotype, thus revealing a regulatory link between cuticle and flavonoid biosynthesis. This study identified a null allele of CD2 and further extended the role of CD2 to multiple pathways operating within the epidermis that have evolved as adaptations to stress thus revealing its role as a master regulator of epidermal cell function.;In tomato, a latitudinal gradient of chloroplast development exists, which leads to the formation of a green shoulder at the peduncle end of the fruit that positively impacts the nutrient content of ripe fruit. Fruit of the ug mutant lack the green shoulder surrounding the calyx. Positional cloning revealed that UG encodes TKN4 , a class I Knotted1-like homeobox (KNOX) TF. KNOX genes typically influence plant morphology through maintenance of meristem activity. However, this research identified a previously undefined role for these TFs in the establishment of chloroplast gradients in tomato fruit through regulating the expression of the GOLDEN 2-LIKE TF, SlGLK2, and it's distant homolog ARABIDOPSIS PSEUDORESPONSE REGULATOR-LIKE (SlAPRR2-LIKE). This study has identified an atypical role for KNOX in regulating fleshy fruit development and defined functional interactions between well-studied, yet previously disparate, TFs that influence fruit chloroplast development.;Fruit of the p mutant are dull, covered by dense trichomes with altered epidermal cell structure and cuticular composition. Fruit of the ep mutant can be peeled easily with limited damage to the underlying pericarp cells. Inter-specific crosses of p and ep mutants with S. pimpinellifolium were performed to generate F2 mapping populations that were screened with genetic markers to assign the mutant loci to chromosomes 2 and 8, respectively, although the mapping is still in progress. The aim of this research is to ultimately isolate these mutant loci by positional cloning and perform functional analysis of each gene. Together, the work presented in this dissertation expands the current knowledge base on the molecular factors that influence fruit development. |
