Christoph Edner
For many years researchers have investigated the effects of drought on the metabolism of plants. They found out various mechanisms, which plants employ to avoid damage to their cells or to the whole plant. To prevent water loss in the short term plants close their stomata, small openings in the leaf surface. This response is rapid and occurs within minutes after the water conditions are altered. In the long run plants adjust to water deficit by reducing leaf size and inducing root growth. But how are these physiological changes mediated in the plant? A plant hormone, called abscisic acid (ABA), is known to be involved in the plant’s response to environmental stresses, including drought stress. It is a major objective to unravel the ABA signalling cascade and to identify the parts and regulators of this important pathway.
Researchers use the well-characterised plant Arabidopsis thaliana , whose genome is sequenced and which can be subjected to genetic modification very easily. They have isolated different mutant plants, which are insensitive to ABA and called them abi mutants. That means these plants are not able to sense ABA and therefore are impaired in the drought stress response, which means that they look wilty after drought treatment.
The ABA-mediated adaptation to changing water availability involves changes in the expression of certain genes. I investigated two genes that code for so called transcription factors, proteins that affect the expression of other genes.
I examined the expression pattern of the gene ATHB12 after drought treatment of
Arabidopsis seedling using the northern blot technique. With this method RNA is transferred onto a nylon membrane and hybridised to a labelled gene specific probe. The amount of messenger RNA of the investigated gene can be quantified by this means. I found out that the gene is strongly induced by drought treatment but shows a reduced expression in the abi mutant background. This leads to the conclusion that the ATHB12 expression is dependent on the protein products of the ABI genes.
The second part of my work consisted of a transactivation assay. Tiny DNA-coated gold particles were shot into Arabidopsis leaves using a particle delivery system, which works with highly pressurised gas. Two plasmids, circular DNA molecules, were transferred into the cells, one carrying the transacting gene and the other one carrying a reporter gene preceded by the binding sequence of the respective transacting gene. The transacting gene codes for the above mentioned transcription factor, which in turn binds to its specific sequence on the second plasmid and activates the reporter gene.
I bombarded Arabidopsis wild type leaves with either ATHB7 or ATHB12 acting as transacting genes and found out that both genes are capable of inducing the reporter gene.
This result demonstrates that both genes encode transcriptional activators, which can induce expression of target genes.
Degree project in Biology
Examensarbete i biologi, 10 p fall 2002
Department of Physiological Botany, Uppsala University
Supervisor: Eva Söderman