Comparative analysis of gene expression in response to cold stress in diverse rice genotypes.

Cold stress is a major factor affecting rice (Oryza sativa) growth and productivity, limiting its distribution worldwide. Rice production is affected primarily due to its vulnerability to cold stress at seedling stage, as well as reproductive stage leading to spikelet sterility. We report here the analysis of 21 diverse rice genotypes from the USDA mini-core collection for cold tolerance and categorized their tolerance levels on the basis of reduction in growth measured by root and shoot length. The screening identified 12 cold tolerant genotypes from which six tolerant genotypes were characterized at the vegetative stage for cold tolerance and gas-exchange parameters. Two tolerant and two sensitive genotypes were used further for gene expression analysis. Lipid Transfer Protein (LTP) genes showed a clear difference in expression between cold tolerant and sensitive genotypes suggesting that they are good candidates for engineering cold tolerance in rice. Nipponbare was identified as a cold tolerant genotype with stress tolerance mechanism potentially operating via both ABA dependent and independent pathways.