Metabolic and transcriptional profiling of cold response in Fragaria vesca

ABSTRACT - Cold response and freezing tolerance of perennial crops is of major interest for Norwegian breeders and farmers due to short vegetation periods and harsh climatic conditions. One of the most important crops for the Norwegian market is the cultivated strawberry (Fragaria  ananassa Duch.). Successful production and berry yield relies mainly on the plants’ cold acclimation, winter survival and re-growth in spring time. Based on joint research intents and national/ international co-operation, the present study was aimed at investigating the functional short- but also long-term cold response in strawberry leaves upon exposure to 2C after 0, 3, 24, 72 and 240 h, using the diploid Fragaria vesca (woodland strawberry) as a model plant. Due to the molecular complexity of cold and freezing tolerance mechanism in plants, distinct but related approaches of metabolic profiling (primary and secondary metabolites by GC-MS) and transcriptional profiling (microarray) were adapted. Preliminary results from transcriptional profiling (Arabidopsis Operon) of Fragaria vesca leaves (clone Ås) have shown the up-regulation of proteins related to cryoprotection (dehydrins), membrane and transport function (COR proteins) and metabolism after 24 h. In addition, the induction of distinct secondary metabolites (terpenes) was confirmed by metabolic profiling based on SPME/ GC-MS analyses. Detailed GC-MS/TOF-based profiling of cold-treated Norwegian Fragaria vesca clones (Ås, Tingvoll, Alta) revealed the functional regulation of soluble compounds such as sugars (glucose, fructose, galactose, raffinose, mannose), amino acids (glutamine, glutamic acid, asparagine and aspartic acid), TCA intermediates (malic acid and fumaric acid) but also distinct secondary metabolites. As already indicated through microarray analyses, galactinol (transient peak after 72 h), and also raffinose, galactose, glucose and fructose (main peak after 240 h) were clearly induced as an effect of cold adaption. In general, primary metabolism was differentially regulated when comparing the three Fragaria vesca clones from South, Mid- and North Norway.