Isolation of Auxin Signal Transduction Mutants in Arabidopsis

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

The plant hormone auxin is involved in many aspects of growth and development, yet little is known about exactly how this hormone causes changes within plant cells. It is known that when plant cells are exposed to auxin, certain genes are activated: without auxin, they are not expressed (i.e., their protein products are not made), and with auxin they rapidly become expressed at high levels. It is also known that specific DNA sequences within the promoters of these genes (i.e, the parts of the genes that control when and where the genes are expressed) are needed for this response to auxin. An unknown number of molecules are involved in recognizing auxin after it enters the plant cell, and causing these genes to be activated. The goal of this project is to identify some of the molecules involved in this "auxin signal transduction" process. The genetic approach taken in this project involves making mutants in the model plant Arabidopsis that show aberrant expression of auxin-responsive genes. Towards this end, transgenic plants were generated that carried engineered selectable marker genes controlled by auxin responsive promoters. The transgenic plants were mutagenized, then seeds from these plants were grown under conditions that allowed for the selection of plants that showed aberrant expression of the selectable marker genes. One of the selectable markers used was a gene that confers resistance to the antibiotic hygromycin. Non-mutant, transgenic plants were killed by the antibiotic, because they did not contain enough auxin to switch on the resistance gene. However, a few mutant plants were able to grow, because the resistance gene was expressed more highly in them than in non-mutant plants. The other selectable marker used was a gene encoding the enzyme alcohol dehydrogenase (ADH). ADH converts allyl alcohol to a toxic substance, acrolein. Non-mutant transgenic plants that were treated first with auxin, then with allyl alcohol, were killed because the ADH gene was switched on by the auxin treatment. However a few mutant plants survived the treatments because the ADH gene was expressed at lower levels in them. One hypothesis is that these mutant lines contain alterations in the molecules involved in responding to auxin. For some of the mutants, this hypothesis has been tested by seeing if other auxin responsive genes, in addition to the selectable marker genes, show altered expression in the mutants. One goal of thsi project is to continue identifying new mutants that show altered expression of auxin-responsive genes. A few of these mutants will be analyzed in detail, and the mutant genes will be cloned in order to discover what molecules they encode. This work has great potential to enhance our understanding of both plant hormone biology, and signal transduction processes in plants.