Genetic studies in Arabidopsis: The characterization of THUNDERHEAD and examining the two-gene hypothesis of glyphosate resistance.

摘要

Plant growth depends on communication pathways where morphogenetic signals are exchanged between cells either laterally within the tissue layer or across boundaries separating epidermal tissues through a complex biological matrix, the cuticle. Therefore, changing the permeability of this medium to signaling factors could regulate plant development. A variety of genes in Arabidopsis have been identified that are involved in this regulation process. The work described here deals with the isolation and characterization of the one such regulatory gene, the THUNDERHEAD (THD) gene. THD encodes an R2-R3 MYB transcription factor and shares sequence similarities with MIXTA, a gene that has been implicated in the development of conical cells.; Glyphosate is a semi-selective, postemergence-applied herbicide. Despite heavy selection pressure, glyphosate resistant weeds have been rare events. Over the past few years, glyphosate resistance in weedy species has been found and the list of resistant weeds has been growing steadily. Resistance in these species was originally hypothesized to be due to an amino acid substitution in the 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) protein, the target site of gyphosate. Specifically, a proline was changed to a serine or threonine in the EPSPS from these resistant species. However, multiple mutageneses of wild-type Arabidopsis have yielded no glyphosate resistant mutants suggesting that no single gene is sufficient to confer resistance to glyphosate. Based on these data it is hypothesized that glyphosate resistance is conferred by a two-gene system. One gene is EPSPS harboring either a serine or threonine in place of the active site proline. The second gene is unknown. To test the two-gene hypothesis transgenic Arabidopsis plants were generated that harbor one of two forms of the EPSPS. These plants were then mutagenized and mutant progeny were screened for second-site enhancers of resistance. Here I report on the resistance conferred by the introduction of these transgenes and the isolation of putative mutants exhibiting enhanced glyphosate resistance.