"Review of literatureCAT CAT is an important antioxidant enzyme known to involve the removal ofH O generated in peroxisomes during ß-oxidation of fatty acids and photorespiration.2 2 CAT is a tetrameric heme-containing enzyme, which has the capacity to directlydismutate, H O to H O and O during stress conditions (Garg and Manchandan, 2009).2 2 2 2 CAT occurs in multiple forms like CAT-1, CAT-2, and CAT-3 which differ in bothmolecular and biochemical properties (Scandalios et al., 1997). CAT genes are knownto involve in imparting tolerance to various biotic and abiotic stresses.The overexpression of E.coli CAT in transgenic Oryza sativa plants conferredsalt stress tolerance (Nagamiya et al., 2007). Transgenic rice plants overexpressingOsMT1a a metallothionein gene has shown enhanced drought tolerance. The expressionof OsMT1a gene has enhanced the antioxidative enzymes like APX, CAT and PODwhich lead to drought tolerance (Yang et al., 2009). It was also reported that theexpression of wheat CAT gene has improved the cold stress tolerance in transgenic riceplant (Matsumura et al., 2002). Molecular responses of plants to drought stressProteomic analysisBeing a sessile organism Plants depends on the proteomic flexibility to shapethemselves during developmental change and in response to biotic and abiotic stresses.Quantitative and qualitative analyses of gene expression and products at differentlevels are necessary to understand these changes. Proteomics is becoming a powerfultool to understand the complex response of plants to environmental stimuli.Proteomics makes an important connection between transcriptome and metabolome(Gray and Heath, 2005) and to analyze biochemical pathways and the complexresponse of plants to environmental stimuli (Qureshi et al., 2007).19 Review of literatureTranscriptomic analysisPresent day researchers are focused on understanding the mechanism of plantresponse to water limited conditions in order to identify gene products that conferadaptation to water stress. The tolerant species might have better mechanisms tosurvive the stress probably due to the presence of novel genes or functionally superiorgene products compared to susceptible species. This has been clearly shown in stresstolerant species, such as Craterostigma plantagineum under dehydration stress.Analysis of expressed sequence tags (ESTs) in this species has revealed the presenceof novel genes induced by dehydration stress (Bartels et al., 1990). Usingtranscriptome analysis a wide range of WRKY Transcription factors (TFs) wereidentified from wheat plants infected with leaf rust (Satapathy et al., 2014)Hence identification and functional characterization of genes that respond todrought from stress adapted species may provide valuable information on geneticengineering for improved tolerance to drought stress. The microarray is the recenttechnique developed to identify the expression profiles of a large number of genes.Expression of Stress-inducible gene, tissue-specific gene expression, mutant geneexpression and transgenic gene expression can be identified through microarraytechnique (Seki et al., 2001; Obayashi et al., 2014). Expression profiling of alteredgenes under multiple stresses has been reported in several species. Expression ofdifferent stress-inducible genes was reported by various workers (Vij and Tyagi, 2007).A wide range of microarrays was identified from Arabidopsis, rice, soybean, poplar,grape, alfalfa, and maize (Obayashi et al., 2014).However, the cost of genome sequencing or generation of microarrays haslimited the use of this technology. ESTs generated from cDNA clones are costeffective and proven to be an efficient strategy to discover novel genes in tolerance to20 Review of literatureenvironmental stresses (Gupta et al., 2010). Analysis of ESTs in several speciesrevealed that many functional, as well as regulatory genes, are up-regulated understress.Table 1: Few databases available for the identification of stress-responsivegenes.Database Name Web link Abiotic stress treatmentsAtGenExpress/Abiotic http://www.Arabidopsis.org/ Cold,Drought,stress series/NASCportals/expression/microarra Osmotic,Oxidative, Salt and arrays y/ ATGenExpress.jsp Heat stressesMicroarray Expression http://rarge.gsc.riken.jp/micr Cold, Drought, NaCl, Light, Database (MAEDA),o array/microarray_expgene. ABARIKEN, Japan. plplantstress.com www.plantstress.com/biotec Drought Oxidative stress,h/index.asp?Flag=1 ABA, cold, saltRegulation of gene expression under drought stressThe primary response of plants to stress is the transcriptional regulation of geneexpression. The signals that activate TFs to bring about gene expression have greatersignificance in plant adaptation. Therefore, the basic goal of plant biology is to gain abetter knowledge of signaling pathways controlling the molecular and cellularmechanisms underlying stress acclimation. Such an understanding of the components ofstress signal transduction will provide venues for improving stress tolerance (Bakshiand Oelmüller, 2014; Chen et al., 2012a; Ishihama and Yoshioka, 2012).Signal perception Signals are specific to a sensor that can specifically transduce the signal totargets. Two major types of proteins are involved in the responses to environmentalstress ‘effector proteins’ and ‘regulatory proteins’, which are involved in signalperception and signal transduction (Bakshi and Oelmüller, 2014). Drought or waterstress causes a change in osmotic potential across the membrane which decreases the21 "