| dc.description.abstract | Ethylene is a gaseous phytohormone with a very simple chemical structure. In higher plants, ethylene is involved in regulation of many aspects of plant growth and development. To gain more understanding about ethylene biology, a chemical genetics approach was employed to first screen for small molecules interfering with ethylene response in Arabidopsis thaliana and subsequently to identify and characterize mutants resistant to the hit compounds.
A group of small molecules with a quinazolinone backbone were identified from a phenotype-based screening of a collection of 10,000 chemical compounds to score suppression of the triple response in etiolated ethylene overproducer 1 (eto1) seedlings. These identified small molecules, named hit compounds, were used to screen Arabidopsis mutants, named revert to eto1 (ret), with restoration of the eto1 phenotype in the presence of hit compounds. There were 7 and 13 ret mutants were identified from collections of Arabidopsis seeds mutagenized by T-DNA insertional activation tagging and ethane methyl sulfonate (EMS) , respectively.
The main objective of my thesis research is to characterize one of the ret mutants, ret41, which was identified from the T-DNA activation tagging mutant collection. In addition to exhibit constitutive triple response in the presence of hit compounds, ret41 has a complex phenotype consisting of dwarf stature, round leaves, reduced male fertility, loss of apical dominance and delayed flowering time in rosette plants. Genetic analysis indicates that ret41 is a single allele recessive mutation. Results from Southern blot analysis indicate that there are 5 T-DNA insertions. By using TAIL-PCR (Thermal asymmetric interlaced PCR) and plasmid rescue methods, I identified 2 of the insertion sites. However, neither of the insertions co-segregates with the phenotype of ret41 by genotyping data, suggesting that the mapped insertions are not likely responsible for ret41 phenotype. Further analysis revealed that the triple response phenotype in etiolated ret41 seedlings was maintained in the presence of inhibitor of ethylene biosynthesis and antagonist of ethylene perception, which suggests that RET41 may function downstream of ethylene receptors. Moreover, the etiolated phenotype of ret41 is independent of eto1-5 allele and ret41 is not allelic to ctr1. Homozygous ret41 mutant showed a severe defect in fertility to produce seeds. There is no significant difference in pollen viability and morphology between ret41 and wild type or eto1 plants. However, the anthers of ret41 are smaller and the pistils are shorter than those in wild type. Microscopic analyses suggested that unusual development of stigmata and differential growth of stamens and pistils are plausible causes for unsuccessful pollination in ret41 mutant to result in sterility. Future work to clone and characterize the gene mutated in ret41 will provide insightful information of the involvement of ethylene in different stages of plant development.
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