Abiotic Stress Gene Families in the Diploid Strawberry, Fragaria Vesca

Strawberry is an herbaceous perennial member of the Rosaceae family, which includes several important fruit crops as well as ornamentals.  The commercial dessert strawberry, Fragaria xananssa, is octoploid and not readily amenable to genetic and genomic research. Genetic and genomic resources are rapidly being developed for the diploid woodland strawberry, F. vesca, so that it can be used as a model system for Fragaria, as well as for other members of the Rosaceae family that are more difficult to transform or work with in the laboratory. One of these resources is a set of about 42,000 ESTs generated from five separate cDNA libraries representing transcripts from water, temperature and osmotically stressed seedlings and plants. These ESTs were assembled into 11,836 contigs and singletons, and these sequences were annotated using gene ontology (GO) terms. Over 1,200 sequences with no match to available Rosaceae ESTs were found, including 6 that were assigned the “response to stress” GO category. The largest number of different transcripts was found in response to cold treatment, while the highest numbers of ESTs for a specific sequence were found with high temperature or with high temperature in combination with osmotic stress. Temperature stress resulted in the highest number of sequences in the “response to stress” GO category.  cDNA libraries were not normalized or subtracted in order to retain members of known stress gene families. As expected,  among the twenty most abundant sequences found in the EST set are seventeen that encode well-known stress response proteins, including metallothioneins, a dehydrin, a secretory peroxidase, and low molecular weight heat shock proteins (LMW HSP), all of which are found to belong to small gene families. Several stress gene families, LMW HSP, HSP70, dehydrin, and others were found and analyzed for homology to sequences from Arabidopsis. The abundance of specific family members in each stress library was used as an indication of expression of the corresponding gene. Predicted stress expression patterns in different plant tissues are being confirmed by RTPCR, with an emphasis on expression in reproductive organs in response to abiotic stresses.