Molecular genetic analysis of fruit development in tomato (Lycopersicon esculentum, Mill.).

摘要

Plant hormones regulate progression through the different phases of plant development in response to endogenous and environmental cues. Gene expression studies, as well as genetic and molecular analysis of mutants with altered hormonal responses, are two common approaches to elucidate hormone response pathways.; This dissertation compares ovary and fruit development in both wild-type tomatoes and the diageotropica (dgt) auxin-resistant mutant, and analyzes the interactions between the plant hormones auxin and ethylene that regulate gravitropism and lateral root formation. Fruit development is dramatically affected by the dgt mutation; resulting in reduced fruit weight, lower numbers of locules and seeds, delayed time to flowering, and extended developmental time between anthesis and the onset of fruit ripening. Relative quantification of expression patterns for genes involved in ethylene biosynthesis (the ACC synthase, LeACS, gene family) and auxin responsiveness (the Aux/IAA, LeIAA, family of auxin responsive genes) was used to provide insights into the involvement of auxin and ethylene in the regulation of fruit development in tomato. Only a subset of the LeACS and LeIAA gene family members are affected by the dgt lesion, specifically at early stages of fruit development.; Changes in cell number and size during ovary and early fruit development were monitored by microscopic analysis. The difference in final fruit size between dgt and wild-type tomatoes correlates with differences in cell number and size that are established pre-anthesis. Differences in the percentage of nuclei present at 2C and 4C at pre-anthesis and anthesis in dgt versus wild-type ovaries suggests a possible delay in cell cycle progression in the dgt ovaries. The expression of four LeIAA genes exhibited differential developmental specificity in developing fruits, as well as differential regulation by the DGT gene product.; Interactions between auxin and ethylene were further investigated by analyzing gravitropic responsiveness and lateral root formation in dgt and ethylene-resistant Never-ripe ( Nr) tomato seedlings, F1, and backcross populations. The Nr lesion has no effect on the reduced gravitropic response of dgt plants, while the dgt mutant is partially dominant with respect to gravitropism. In regard to lateral root formation, dgt is completely recessive and seems to be epistatic to Nr.