EFB530 Plant Physiology

Arabidopsis as a model system: Genetics, gene expression, and genomics

Advantages of Arabidopsis thaliana for plant research

• small-can grow alot in a small space
• has one of the smallest plant genomes (only 5 chromosomes, little repetitive DNA)
• self-fertile, short generation time
• lots of genetic mutants available
• excellent genetic map has been produced (complete sequence of genome was completed and published in December 14, 2000 issue of Nature)
• lots of molecular tools have been developed, mostly to allow rapid cloning of genes

Discovering all of the genes in a plant=sequencing of the Arabidopsis genome

• ultimate genetic map, which will make it very easy to identify which gene is mutated in a mutant plant
• will allow us to study the complete picture of all of the genes for a particular function (many proteins are encoded by several slightly different genes=multigene family)
• will allow us to study patterns of gene expression on a large scale (1000's of genes at a time) in response to stimuli or development
• allow us to study the evolutionary relationships of whole chromosomes from different organisms (E. coli, yeast, and a nematode are already completely sequenced; Drosophila and Arabidopsis are next, then human)

A very powerful approach to discovering fundamental information about an organism is to identify mutants

• the phenotype of a mutant can tell you alot about the normal function of that gene
• once you've found a mutant, you would map that to a particular spot on a chromosome
• Arabidopsis has a very detailed map, which allows very precise localization on a chromosome
• once localized, one can obtain a DNA clone corresponding to that spot on the chromosome, then identify the gene that is mutated
• the type of protein encoded by that gene tells you alot about how that particular plant function (which you mutated) normally works

Once you have the DNA sequence of a gene, one might want to see the effect of a mutation in that gene on plant function

• random insertions of transposons or Agrobacterium T-DNA can introduce mutations
• people have made large "libraries" of random insertion mutants
• using the sequence of the gene you have, one can find a plant that has an insertion mutation in that gene, then observe the phenotype of mutating that gene

Using technology, we can study the expression of 1000's of genes simultaneously

• thousands of cloned gene can be bound to a tiny glass slide using a robot
• RNA is hybridized to this glass slide with the clones
• a laser scanner detects how much RNA has stuck to the cloned genes on the slide

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