Freezing tolerance in plants develops through acclimation to cold by growth at low, above-freezing temperatures. Wheat is one of the most freezing-tolerant plants among major crop species and the wide range of freezing tolerance among wheat cultivars makes it an excellent model for investigation of the genetic basis of cold tolerance. Large numbers of genes are known to have altered levels of expression during the period of cold acclimation and there is keen interest in deciphering the signaling and regulatory pathways that control the changes in gene expression associated with acquired freezing tolerance. A 5740 feature cDNA amplicon microarray that was enriched for signal transduction and regulatory genes was constructed to compare changes in gene expression in a highly cold-tolerant winter wheat cultivar CDC Clair and a less tolerant spring cultivar, Quantum. Changes in gene expression over a time course of 14 days detected over 450 genes that were regulated by cold treatment and were differentially regulated between spring and winter cultivars, of these 130 are signaling or regulatory gene candidates, including: transcription factors, protein kinases, ubiquitin ligases and GTP, RNA and calcium binding proteins. Dynamic changes in transcript levels were seen at all periods of cold acclimation in both cultivars. There was an initial burst of gene activity detectable during the first day of CA, during which 90% of all genes with increases in transcript levels became clearly detectable and early expression differential between the two cultivars became more disparate with each successive period of cold acclimation.
MicroRNAs (miRNAs) and the mRNA targets of miRNAs were identified by sequence complementarity within a DNA sequence database for species of the Triticeae. Data screening identified 28 miRNA precursor sequences from 15 miRNA families that contained conserved mature miRNA sequences within predicted stem-loop structures. In addition, the identification of 337 target sequences among Triticeae genes provided further evidence of the existence of 26 miRNA families in the cereals. MicroRNA targets included genes that are homologous to known targets in diverse model species as well as novel targets. MicroRNA precursors and targets were identified in 10 related species, though the great majority of them were identified in bread wheat, Triticum aestivum, and barley, Hordeum vulgare, the two species with the largest EST data sets among the Triticeae.
Background: Wheat is an excellent species to study freezing tolerance and other abiotic stresses. However, the sequence of the wheat genome has not been completely characterized due to its complexity and large size. To circumvent this obstacle and identify genes involved in cold acclimation and associated stresses, a large scale EST sequencing approach was undertaken by the Functional Genomics of Abiotic Stress (FGAS) project.
Using microarray analysis, we identified regulatory and signaling-related genes with differential expression in three genotypes with varying degrees of salt tolerance, Triticum aestivum , the amphiploid, and the wheat substitution line DS3E(3A). Lophopyrum elongatum is among one of the most salt-tolerant members of the Triticeae; important genetic stocks developed from crosses between wheat and L. elongatum provide a unique opportunity to compare gene expression in response to salt stress between these highly related species. The octaploid amphiploid contains the entire genome of T. aestivum and L. elongatum, and the disomic substitution line DS3E(3A) has chromosome 3A of wheat replaced by chromosome 3E of L. elongatum. In this study, microarray analysis was used to characterize gene expression profiles in the roots of three genotypes, Triticum aestivum, the octaploid amphiploid, and the wheat DS3E(3A) substitution line, in response to salt stress. We first examined changes in gene expression in wheat over a time course of 3 days of salt stress, and then compared changes in gene expression in wheat, the T. aestivum × L. elongatum amphiploid, and in the DS3E(3A) substitution line after 3 days of salt stress. In the time course experiment, 237 genes had 1.5 fold or greater change at least one out of three time points assayed in the experiment. The comparison between the three genotypes revealed 304 genes with significant differences in changes of expression between the genotypes. Forty-two of these genes had at least a twofold change in expression in response to salt treatment; 18 of these genes have signaling or regulatory function. Genes with significant differences in induction or repression between genotypes included transcription factors, protein kinases, ubiquitin ligases and genes related to phospholipid signaling.
Common and dwarf bunt (Tilletia caries (DC.) Tul & C. Tul, T. foetida (Wallr.) Liro and T. controversa (Kühn) are potentially important wheat diseases in Romania, especially in organic farming and on small farms, unable in most cases to properly treat the seed. Growing bunt resistant cultivars can be an efficient way to reduce expenses and protect the environment, by reducing use of pesticides. For these reasons, a small breeding program was started in 1972, by crossing the old Turkish wheat PI 178383 (a Bt9 and Bt10 carrier) with adapted cultivars. Later, in an attempt to diversify the resistance genes used in the program, several gene sources (including Bt5, Bt8, Bt11, Bt12 etc.), received from Dr. Bob Metzger (Oregon State University, U.S.) were used as parents. Since, our research effort has focused on: (1) continuously checking the efficiency of known bunt resistance genes against local populations (isolates) of bunt; (2) improving the competitiveness of bunt resistant germplasm by repeated cycles of crossing with adapted cultivars and selection for both bunt resistance and agronomic type and (3) searching for new bunt resistance genes. (1) About ten years of artificial testing with 6-10 isolates/year of bunt collected from Romanian locations representative for natural occurrence of Tilletia species, has constantly shown that Bt5, Bt10, Bt11, Bt12 expressed a high level of resistance. Along with original sources provided primarily by Dr. Bob Metzger and more recently, also by Prof. Blair Goates (National Small Grains Germplasm Research Facility, West Aberdeen, U.S.), advanced lines carrying the most efficient genes were tested and confirmed the transfer of this trait. (2) All bunt resistance gene sources available to us were very tall, susceptible to powdery mildew and leaf rust, were low yielding and had poor baking quality. Progress in improving the competitiveness of bunt resistant lines in the absence of bunt has been slow, but every new cycle has shown definite improvements over the previous ones. Presently available bunt resistant lines are semidwarf and powdery mildew resistant, are better adapted to local conditions and give yields of 90-100% as compared with current check cultivars. They are still deficient in leaf rust resistance and bread making quality. New lines with improved leaf rust resistance and quality are in preliminary yield tests. Accelerated progress is expected by using molecular markers for some of the bunt resistance genes. Markers will also be used to pyramid resistance genes. (3) Search for new bunt resistance sources has identified two potential sources with resistance, presumably coming from the Brazilian cultivar Colonias and from the rye genome. Further testing with a wider range of bunt isolates is under way. Positive experience in accelerated selection of higher resistance to other wheat pathogens, accumulated from larger forms of trans-national cooperation (ring tests), emphasized the need of such approach with regard to common bunt, too. The XV th Biennial Work...
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