Identification Hierarchical Selection of Expressed Sequence Tags and their Expression under Drought Stress in Rice

<ns2:p>The key components of drought-stress signaling that are responsible for drought tolerance in rice have not been identified yet. Although many expressed sequence tags (ESTs) of rice grown under drought stress have been identified and deposited in the GenBank, they have not been optimally used for functional analyzes. This research was thus established to analyze an EST dataset in order to understand the global gene expression profile induced by drought stress in rice, to discover novel droughttolerance genes using in silico study, and to confirm them through qRT-PCR analysis. A dataset of drought-response-related ESTs in rice was downloaded from the NCBI, preprocessed and grouped into clusters for functional analysis to obtain stressresponsive contigs. These contigs were then hierarchically selected to identify those related to transcription factors. The selected contigs were then incorporated into the drought-tolerant QTL on rice physical maps. The gene expression of each selected locus was evaluated in rice cv. Hawara Bunar and IR64 under drought stress. Gene Ontology analysis showed that the contigs consisted of genes encoding proteins involved in metabolic and cellular processes, related to catalytic and binding function, and located in the nucleus, cell membrane, and endomembrane organelles. Ten candidate genes potentially involved in regulating tolerance of drought stress were identified. They were located on rice chromosomes 1, 2, 3, 4, 6 and 9, and colocalized with the QTL for the drought-tolerance trait. Based on in silico and qRT-PCR analyzes, Os03g0160100, Os03g0815100, Os06g0601000 and Os09g0553100 were considered to be candidates for uncharacterized drought-responsive regulatory genes that potentially being used for manipulating drought tolerance in rice.</ns2:p>