Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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A.K. Tyagi, S. Vij and N. Saini
Table 1. Continued...
Arabidopsis Responses elicited by b-~8300 Whitham et al.
thaliana diverse RNA viruses in
susceptible hosts (2003)
Oryza sativa Environmental, biological b- 21,000 Cooper et al.
and chemical stress (2003)
treatments
Zea mays Endosperm and placenta/ a->5000 Yu and Setter
pedicel tissues in (2003)
developing kernels under
water stress
Nicotiana Resistance against a- 298 Hugot et al.
tabacum oomycetes (2004)
Populus Salt stress a- 315 Gu et al. (2004)
euphratica
a: cDNA microarray; b: oligonucleotide microarray
3.1. Positional Cloning
The traditional approach to generate mutants through chemical or physical mutagenesis
and identify mutants by using screens for specific stresses has been found useful.
Access to the mutated gene is obtained using various positional cloning strategies.
The map-based cloning strategy identifies the gene based on mutant phenotype by
identifying linkage to markers whose physical location in genome is already known.
The disadvantage of this method of identifying genes for stress response was the
effort required to make a physical map to develop markers for identifying the genetic
locus to be followed by cloning, determining the sequence of the region and validation
of gene function through complementation (Jander et al., 2002). Thus, such a method
could not be used for large-scale gene identification. There have been several advances
like the sequencing of the Arabidopsis and rice genomes, availability of markers
and advances in methods to detect DNA polymorphisms including SNPs, over the past
few years due to which positional cloning can be considered as an option for functional
genomics. The Arabidopsis Information Resource (TAIR) provides integrated data for
over 4,000 genetic markers and 90,000 polymorphisms (Garcia-Hernandez et al., 2002).
Similarly, a large number of markers are also available for rice, including 3267 markers
available at RGP, Japan (http://rgp.dna.affrc.go.jp/publicdata/genetic map 2000/
index.html), 171 CAPS markers (Harushima et al., 1998) and over 2000 SSR markers
(Akagi et al., 1996; Chen et al., 1997; Temnykh et al., 2000; McCouch et al., 2002).