4. Development of mutant populations

The use of mutant populations of plants, developed through insertional mutagenesis is an important tool to dissect the functions of abiotic stress-related genes [23]. Insertional mutagenesis is accomplished through T-DNA or transposable elements. Such mutant populations are available for Arabidopsis and rice plants. These saturation mutant populations of Arabidopsis and rice cover more than 90% of their genes that could be employed for characterization of abiotic stress tolerance genes [24]. Development of high throughput genomic platforms such as serial analysis of gene expression (SAGE), HRM (differential display, high resolution melt) analysis, TILLING, microarray, etc. have made rapid analysis of these mutation events. A large number of abiotic stress-related genes have been identified using Arabidopsis and rice knockout populations. In a 250,000 independent T-DNA insertional Arabidopsis population, more than 200 mutants were found with altered stress responses. Some of these include mutations in genes encoding transcription factors, ABA biosynthetic enzymes and sodium transporter high affinity K+ transporter (HKT1) [25]. Recent progress on the generation of T-DNA insertion lines have been reviewed in several articles [26, 27].

Along with T-DNA and transposable elements based mutant populations; the need for alternative means of studying gene function is growing day by day. This is mainly because of the low number of Arabidopsis and rice tagged genes that code for clear phenotypes [28]. Recently, traps and activation tagging have been focused as the alternative means of gene tagging [29, 30]. Trap and activation techniques have been widely used for generation of tagged populations of Arabidopsis and rice.
