ARABIDOPSIS - A Model Organism

INDEX :• INTRODUCTION• GENOME LIFE CYCLE• EASE OF TRANSFORMATION

EPIGENETICS• RESPONSE TO ENVIRONMENT.

INTRODUCTION :• Arabidopsis is a popular model organism used in

plant biology and genetics.• It is a small flowering weed.• Grows luxuriantly in temperate regions of the world.• It is also known as thale cress, mouse-ear cress or

Arabidopsis.• Named after 16th Century botanist JOHANNES THAL.• Laibach - First to recognize the potential of

Arabidopsis as a model organism (in mid 90's).• It is 20–25 cm tall.

THE GENOME LIFE CYCLE :

It has a short life cycle.It has a small genome.It has 5 chromosomes.The genome includes

105Mb of euchromatic DNA,15 Mb of seqeunced heterochromatin, and additional of 15-25 Mb satellite repeats and rDNA, thus a total of 140Mb.

EPIGENETICS :It is defined as mutation that is chromosomally inherited but

do not involve a change in nucleotide sequence.These mutation is associated with chemical modification of

DNA.Plants (Arabidopsis) is in epigenetic research for several

decades.Genomes are heavily modified by cytosine methylation

(RNA interference).When male and female germ lines differ imprinting results in

maternally inherited allele.It is prevalant in the extra embryonic endosper tissue.Epigenetics are often influenced by the environment. (Plants

remember cold of winter by flowering in the following spring).

This process is regulated by RNA processing and histone modification in Arabidopsis.

EASE OF TRANSFORMATION OF EPIGENETICS :Agrobacterium tumefaciens induces tumorous growth

due to transfer of hormone biosynthesis gene from bacterial Ti plasmid into chromosome of host plant.

Ti genes are found in the T- DNA portion of the plasmid.Transformation in plants are done by replacing Ti gene

with gene of interest.Arabidopsis can be transformed either by spraying or

dipping them into concentrated culture of Agrobacterium in a surfactant solution.

Stable transformation occurs several days or weeks later infection on the female gametophyte before fertiltzation.

Transformed plants are selected by inducing selectable marker gene (herbicides resistance) on media or soil containing herbicides.

Arabidopsis transformation efficiency is high.

The insertions can be used for reverse genetics.By including transponsable elements in the T-DNA

transposon hops can be generated.Transposons have been the major tool for reverse

genetics in these plants than rice and maize.

RESPONSE TO ENVIRONMENT :The immune system of plants are widely

diversified and can recognize viruses,microbes,worms,insects,etc.

These are biotic stress caused to plants.In addition they also undergo abiotic stress

such as changes in light intensity, circadian rhythm, nutrient, salt and water.

These have various effects on the environment.

Light plays central role in plant biology.Arabidopsis is replacing tobacco and spinach

in photosynthetic research.

RECENT RESEARCH :

Functional Properties of a Cysteine Proteinase from Pineapple Fruit with Improved Resistance to Fungal Pathogens in Arabidopsis thaliana.

REFERENCE : Greilhuber, J., Borsch, T., Müller, K., Worberg, A., Porembski, S.,

and Barthlott, W. (2006). Smallest angiosperm genomes found in Lentibulariaceae, with chromosomes of bacterial size. Plant Biology, 8: 770-777.

D.W. Meinke, J.M. Cherry, C. Dean, S.D. Rounsley, M. Koornneef (1998). "Arabidopsis thaliana: A Model Plant for Genome Analysis". Science 282 (5389): 662–682.

 Coelho SM, Peters AF, Charrier B, et al (2007). "Complex life cycles of multicellular eukaryotes: new approaches based on the use of model organisms". Gene 406 (1–2): 152–70.

 Clough SJ, Bent AF (1998). "Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana". Plant J 16 (6): 735–743. 

Wang W, Zhang L, Guo N, Zhang X, Zhang C, Sun G, Xie J. Functional Properties of a Cysteine Proteinase from Pineapple Fruit with Improved Resistance to Fungal Pathogens in Arabidopsis thaliana. 2014 Feb 21;19(2):2374-89.