Differential and coordinated expression of Cbf and Cor/Lea genes during long-term cold acclimation in two wheat cultivars showing distinct levels of freezing tolerance

Role of DREB transcription factors in abiotic and biotic stress tolerance in plants

Abiotic and biotic stresses negatively influence survival, biomass production and crop yield. Being multigenic as well as a quantitative trait, it is a challenge to understand the molecular basis of abiotic stress tolerance and to manipulate it as compared to biotic stresses. Lately, some transcription factor(s) that regulate the expression of several genes related to stress have been discovered. One such class of the transcription factors is DREB/CBF that binds to drought responsive cis-acting elements. DREBs belong to ERF family of transcription factors consisting of two subclasses, i.e. DREB1/CBF and DREB2 that are induced by cold and dehydration, respectively. The DREBs are apparently involved in biotic stress signaling pathway. It has been possible to engineer stress tolerance in transgenic plants by manipulating the expression of DREBs. This opens an excellent opportunity to develop stress tolerant crops in future. This review intends to focus on the structure, role of DREBs in plant stress signaling and the present status of their deployment in developing stress tolerant transgenic plants.

Wheat EST resources for functional genomics of abiotic stress

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.

Results

We generated 73,521 quality-filtered ESTs from eleven cDNA libraries constructed from wheat plants exposed to various abiotic stresses and at different developmental stages. In addition, 196,041 ESTs for which tracefiles were available from the National Science Foundation wheat EST sequencing program and DuPont were also quality-filtered and used in the analysis. Clustering of the combined ESTs with d2_cluster and TGICL yielded a few large clusters containing several thousand ESTs that were refractory to routine clustering techniques. To resolve this problem, the sequence proximity and "bridges" were identified by an e-value distance graph to manually break clusters into smaller groups. Assembly of the resolved ESTs generated a 75,488 unique sequence set (31,580 contigs and 43,908 singletons/singlets). Digital expression analyses indicated that the FGAS dataset is enriched in stress-regulated genes compared to the other public datasets. Over 43% of the unique sequence set was annotated and classified into functional categories according to Gene Ontology.

Conclusion

We have annotated 29,556 different sequences, an almost 5-fold increase in annotated sequences compared to the available wheat public databases. Digital expression analysis combined with gene annotation helped in the identification of several pathways associated with abiotic stress. The genomic resources and knowledge developed by this project will contribute to a better understanding of the different mechanisms that govern stress tolerance in wheat and other cereals.