Differential Gene Expression in Wheat Under Long-Term Post-Anthesis Heat Stress by Using Microarray and Real-Time PCR Technique.

Long-term post-anthesis high temperature stress is one of the major limiting factors for wheat production globally, including the southern Great Plains areas in USA. The objectives of the research were to study the differential gene expression in heat-tolerant and heat-sensitive wheat lines at long-term high temperature stress. The plants were grown in optimum conditions at growth chamber. In the expression study, the plants were exposed to stress after flowering by gradually increase of temperature from 20/15^o C to 36/30^o C day/night in four days with 80% relative humidity and 16/8 hours day light to simulate natural conditions. Leaf tissue was collected from both heat-treated and control plants at 4, 7, and 10 days. The microarray gene expression study was performed by using Affymetrix gene chip array at only 4 and 7 sampling dates. A total of  337 and 228 genes were up-regulated at day-4 and day-7, respectively. In tolerant lines 41 genes were up-regulated in both dates, while in sensitive lines, 917 and 1045 genes were up-regulated in those sampling dates with a common expression of 236 genes. The putative functions of the ESTs were predicted by BLASTX. The differentially expressed genes were broadly classied according to their function. In the tolerant lines, protein synthesis-, transcription factor-, cell wall synthesis-, signaling-, photosynthesis-, and oxydoreductase genes were higher expressed under stress conditions. On the other hand, genes related to cell wall degradation, senescence, metabolism, and stress had higher expression in heat sensitive liens. The differential expression of fourteen selected transcripts was studied by Real-Time PCR using RNAs of tolerant and sensitive lines, and their parents under stress and optimum conditions. Results from Real-Time PCR confirmed their differential expression. The differential expression of those genes may be attributed to genotypic variations in response to heat stress.