Differential gene expression in Festuca under heat stress conditions

Fescues (Festuca sp.) are major cool-season forage and turf grass species around the world. Heat stress is one of the limiting factors in the production of fescues as forage in the southern Great Plains of the US. Heat responsive gene transcripts were cloned by using suppression subtractive hybridization between a heat-tolerant and a heat-sensitive fescue genotype subjected to a slowly increased temperature mimicking the natural conditions. The temperature in the growth chamber containing the plants was gradually increased from 24 degrees C to 44 degrees C over a period of 2 weeks. Three subtractions were conducted between samples of the two genotypes collected after 12 h of exposure to 39, 42, and 44 degrees C. A total of 2495 ESTs were generated, of which 1800 clustered into 434 contigs and 656 were singlets. The putative functions of ESTs were predicted by BLASTX. Nearly 30% of the contigs and 39% of the singlets had no similarity to GenBank sequences. Differentially expressed genes selected by subtractions were classified into 10 broad categories according to their putative functions generated by BLAST analysis. Under heat-stress conditions, cell maintenance, chloroplast associated and photosynthesis-, protein synthesis-, signalling-, and transcription factor-related genes had higher expression levels in the heat-tolerant genotype. Genes related to metabolism and stress had higher expression in the heat-sensitive genotype. The expression of 17 selected gene transcripts were examined by RT-PCR using plant tissues of the two genotypes grown under heat stress and under optimal temperature conditions (24 degrees C) for fescue. Results from RT-PCR confirmed the differential expressions of these transcripts. The differential expressions of at least 11 of these genes were attributable to heat stress rather than to differences in the genetic backgrounds of the genotypes.