abi3-6 seed

Plant Hormones and why the McCourt lab studies them

Approximately 100 years ago, the German botanist Julian von Sachs suggested that plant growth and development may be controlled by specific endogenous plant substances. Since then plant biologists have identified a number of compounds, termed phytohormones, that at low concentrations influence many diverse developmental processes ranging from seed germination to root, shoot and flower formation. However, even though these compounds have been chemically defined, how phytohormones mediate plant development and growth is still unclear. For example, within a plant, a single hormone can regulate many different processes and at the same time different hormones can influence a single process. Luckily, the application of APOG (Awesome Power Of Genetics) has begun to establish the molecular mechanisms by which plant hormones participate in coordinating plant development.

Developmental genetics of nematodes and Drosophila has been instrumental in determining how a molecular recognition event is converted into a cellular response. Although these systems have unique genetic attributes that simplify the identification of genes involved in a signaling event, conceptually, a major factor in their success has been the use of a biological response that is easily assayed and exquisitely sensitive to minor changes in flux. This has permitted genetic identification of a large number of the components affecting signaling pathways. Thus, aside from identifying major points of control in a pathway, such as transcription factors and cell signaling receptors, such genetic screens permit finer scale dissection of the process. Molecular activities that are essential in a given pathway but only have minor effects on it may also be identified.

With these considerations of dosage sensitivity in mind we have embarked on a program to identify genes that regulate plant hormone signal transduction. We have chosen to study the plant hormone abscisic acid (ABA) in Arabidopsis thaliana as a model to understanding hormone signaling in plants for the following reasons. First, auxotrophic mutations in ABA biosynthesis are not lethal in Arabidopsis. Hence, mutations that alter the signal transduction of this plant growth regulator should be viable. Secondly, most screens that alter the response of Arabidopsis to ABA can be performed at the level of germination on Petri plates. Thus, large numbers of mutagenized seed can be screened with relative ease under conditions where hormone concentrations can be precisely controlled. Although we are primarily interested in ABA we have found that many of our genetic screens identify mutations that affect other hormone signaling pathways. For example, many ABA sensitivity screens uncover mutations that affect gibberellin (GA) biosynthesis/sensitivity or ethylene sensing. This Web page touches on some of the things we do in the lab and some of the genes we run into on our genetic journey's.



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