The auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) has a pleiotropic phenotype including a lack of lateral roots and reduced gravitropic response, apical dominance, vascular development, and fruit growth. The dgt mutation reduces the auxin sensitivity of only a subset of auxin responses while levels, metabolism, and transport of auxin appear normal, suggesting that the Dgt gene encodes a component in an auxin-signaling pathway. This dissertation reports isolation and characterization of the Dgt gene. Delineation of three microsyntenic regions in the Arabidopsis genome containing genes homeologous to genetic markers near the Dgt gene allowed isolation of additional ESTs from the corresponding tomato region, significantly reducing the mapping distance to the dgt locus. Further analysis determined that the Dgt gene encodes a cyclophilin (LeCYP1), a previously unidentified component of auxin signaling. Each known dgt allele contains a unique mutation in the coding sequence of LeCyp1. In addition, the wild-type Dgt gene can complement dgt mutant plants. Cyclophilins characteristically have peptidylprolyl cis-trans isomerase (PPIase) activity, but it is unclear whether that activity is necessary for all of their biological functions. Each allelic dgt mutation reduces or nullifies PPIase activity of LeCYP1 fusion proteins in vitro. Immunoblot analysis indicates that all three dgt mutations are null mutations. Phylogenetic comparisons of tomato and Arabidopsis cytosolic-type cyclophilins could not identify any single Arabidopsis member as orthologous to LeCYP1/DGT. Five T-DNA insertion mutants were analyzed to determine if mutations in Arabidopsis cytosolic-type cyclophilins phenocopy the pleiotropic dgt phenotype. Overall seedling growth and morphology appear normal in the mutants, however, their gravitropic response is slow. The lack of exact phenocopy may be due to the redundant nature of Cyp genes in Arabidopsis, which has over twice as many Cyp genes as tomato. In tomato, the cyclophilin inhibitor cyclosporin A (CsA) inhibits auxin-induced adventitious root initiation and expression of two early auxin response genes, LeIAA10 and 11, that are also affected by the dgt mutation. Taken together, these results suggest that the cyclophilin encoded by the Dgt gene plays an important role in auxin signal transduction. / Graduation date: 2004

published_or_final_version / Botany / Master / Master of Philosophy

It is desirable to develop tomato (Lycopersicon esculentum Mill.) cultivars which have the characteristics of earliness to fit the relatively short and cool growing season in Canada. Earliness was studied by parti-tioning the life cycle of the tomato plant into 7 component growth stages and using these as a basis for attempts to recombine quantitative genes which control the earliness of different stages from different parents to obtain progeny earlier than both parents. The mode of inheritance of the earliness in the 7 growth component stages was studied with 3 approaches. First, a complete diallel cross experiments used 3 parental cultivars: Bonny Best, Immur Prior Beta and Cold Set. The progenies were grown under 2 temperature regimes (17.0-21.0°C and 10.0-13.0°C). The data for days required for each stage were analyzed first by the Hayman and Jinks method which estimated the following 4 genetic parameters; variation due to differences in additive and dominant gene action; asymmetry of positive and negative effects of genes; relative frequencies of dominant and recessive alleles; and 5 genetic estimators: average degree of dominance; proportion of dominant and recessive alleles; ratio of the total numbers of dominant to recessive genes in the parents; number of effective factors which exhibit some degree of dominance and the heritability. The calculated genetic parameters and estimators differed in the 2 temperature regimes indicating there could be differences in gene action such as overdominant instead of partial dominant gene action depending on the temperature conditions. There were differences in heritabilities for the component stages, and some of the longer stages had potentially useful high heritabilities. The data were also analyzed by the Griffing method which estimated the general combining ability and specific combining ability. The analyses showed that both the additive and dominant gene action had significant effects in most of the component stages, and in most cases, the additive variance was larger than the dominant variance. The second approach employed reciprocal cross experiments with 2 parental cultivars, Bonny Best and Immur Prior Beta, and their reciprocal hybrids under the 2 temperature regimes in greenhouses and growth chambers. The nuclear and/or cytoplasmic effect on the 7 growth component stages, net photosynthesis rate and leaf area were studied. There was some evidence that cytoplasmic effects were relatively important for some of these characteristics, and these effects were more noticeable in the cool regime. In the third approach, field selection experiments on the earliness of 2 major stages were commenced in the F₃ of Bonny Best and Immur Prior Beta reciprocal cross populations. The mean values for both stages in the F₅ reciprocal populations were earlier than the 2 original parents indicating recombination of genes for earliness from parental cultivars. These results indicate that the methods which were used in these studies are a feasible way to increase the quantitative characteristic of earliness in the tomato. / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.

The plant hormone auxin regulates many aspects of plant growth and development. At the cellular level, auxin can stimulate cell division, cell elongation, and cell differentiation. Little is known about the molecular mechanisms that mediate auxin action at this level, although changes in gene expression have been implicated in each of them. An important step in elucidating the signal transduction steps involved in these responses is the identification of intermediates that respond to auxin treatment within a physiologically relevant range, and can be functionally linked to specific response(s). The Aux/IAA family of auxin-regulated genes, which has been identified in several species, may constitute such a group of signalling intermediates. This dissertation reports on the isolation and characterization of eleven tomato genes, LeIAA1 - 11, which are homologous to these Aux/IAA genes. Expression characteristics in response to exogenously-applied auxin were determined in segments of etiolated hypocotyls. The LeIAA genes fell into three kinetic classes and displayed differential responsiveness to the treatment. Comparison of auxin-induced expression in wild-type and the auxin-insensitive diageotropica (dgt) mutant revealed that induction of only a subset of genes was affected by the mutation while the other genes retained wild-type response levels in the mutant. This finding indicates that at least two signal transduction chains lead to auxin-induced gene expression, and the dgt gene product acts on only one of them. The expression pattern of nine LeIAA genes was determined in a wide variety of tissue samples in order to link individual LeIAA genes with specific physiological responses. To that end, a qualitative multiplex RT-PCR method was developed that allowed quick assessment of relative expression levels in a large number of small RNA samples. It was found that LeIAA10 expression was highest in tissues undergoing rapid growth, suggesting a role for this gene in the process of cell expansion. The expression of LeIAA1 1 was also variable during development, while LeIAA2 was strongly down-regulated after light treatment. These experiments demonstrated organ-preferential expression of LeIAA genes under the control of environmental factors and depending on developmental stages. The LeIAA genes may thus act as integrators of several other signals with the auxin stimulus. / Graduation date: 1998

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Graduation date: 1994

published_or_final_version / abstract / toc / Botany / Master / Master of Philosophy

published_or_final_version / abstract / Botany / Master / Master of Philosophy