Time: 4:50 PM
Nagendra Singh, Awadhesh Pandit, Pragya Mishra, Sushma Tiwari, Sikha Sinha, Rupesh Deshmukh, Anshul Sharma, Vijay Singh and Vandna Rai
ICAR-National Research Centre on Plant Biotechnology, Pusa Campus, New Delhi-110012
Rice (Oryza sativa) is a staple food for more than half of the global human population. Therefore it is imperative to develop stress tolerant high yielding rice varieties that will produce more from less land and other agricultural inputs. For this superior genes spread out in different in germplasm accessions of the global rice collections need to be identified and brought together in a high yielding super variety of rice. It is pertinent to use high throughput tools such as whole genome microarrays for effcient gene discovery. We have employed Affymetrix whole genome microarray expression arrays to aid discovery of genes for salt tolerance and high grain number in rice. A combination of QTL mapping, whole genome expression profiling and bulked segregant analysis of recombinant inbred lines (RILs) approaches was used to identify genes for salt-tolerance in rice. The extreme tolerant and sensitive RILs were pooled and analysed along with their parents for differential gene expression after imposition of salt stress. Number of up- and down-regulated genes were 798 and 2,407 in tolerant as compared to the sensitive rice cultivar. However, the list of differentially expressed genes was reduced to only 30 after bulk segregant analysis. Among these two genes, an integral membrane protein DUF6 and a cation chloride co-transporter gene were collocated in the QTL region, and hence are potential candidate for salt-tolerance in the tolerant rice variety. Using microarray data a co-expression gene interaction network was also crafted for commonly co-expressed genes during salinity and drought stresses with three major hubs constituted by Myb2 transcription factor, phosphoglycerate kinase and heat shock proteins. The analyses suggested a pivotal role of these genes in salinity and/or drought stress responses. Further, analysis of cis-regulatory elements of commonly differentially expressed genes during salinity and drought stresses revealed the presence of 20 different motifs. Similarly, for identifying gnes for high grain number in a new plant type rice genotype Pusa 1266, a consistent QTL for high grain number qGN4.1 was mapped using Pusa 1266 (high grain number/ Pusa Basmati1 (low grain number) RILs and candidate genes for high grain number were identified using microarray analysis of extreme bulks and parents. A large set of genes (4307) were differentially expressed between the two parents. But the number was reduced to 759 with bulked segregant anlysis. Six genes in qGN4.1 QTL region were differntially expressed but only one a protein kinase domain containng protein was highly upregualted in the bulk. Therefore protein kinase was predicted a potential candidate for high grain number in rice. These results depict the usefulness of microarray analysis for discovering novel genes for salinity stress tolerance and grain number in rice.