S05 - Session O2 - Dehydrins and carbohydrate metabolism associated with cold hardiness of garden roses under natural and controlled conditions

Authors: Lin Ouyang *, Leen Leus, Ellen De Keyser, Marie-Christine Van Labeke

Roses with high economic value are grown and sold worldwide. However, for the garden roses grown in northern regions (Northern Europe, North China, Russia, the northern regions of the US and Canada), winter temperature is a vital environmental factor affecting their survival and ornamental quality, thus limiting their development and marketing. We previously conducted a three-year screening experiment on 17 garden rose genotypes, separating the most cold-hardy genotypes from less cold-hardy genotypes. According to the classification, two cultivars ('Dagmar Hastrup' and 'Chandos Beauty') with distinct cold hardiness levels were selected for this study. We focused on two important metabolic pathways associated with cold hardiness of roses namely the regulation of cryoprotective dehydrins and the changes in carbohydrate metabolism, under both field and controlled conditions. Cold hardiness determined by LT 50 value showed a seasonal/dynamic pattern including cold acclimation (decline of LT 50 value), midwinter hardiness (lowest LT 50 value) and deacclimation (rise of LT 50 value). The more cold-hardy cultivar of 'Dagmar Hastrup' showed a relatively fast cold acclimation and reached significant lower LT 50 value. However, less cold-hardy cultivar of 'Chandos Beauty' acclimated slower and needed extended freezing temperatures to acclimate completely. Dehydrin genes showed a seasonal expression pattern and accumulated between November and January. The expression level of RhDHN5 transcript was consistently up-regulated during cold acclimation, but rapidly suppressed during deacclimation under controlled condtion. A prominent correlation between LT 50 and expression level of RhDHN5 was found in these two cultivars. Soluble sugars accumulated strongly during cold acclimation. Starch-to-sugar conversion and raffinose levels were prominently affected by cold acclimation and deacclimation. Key genes related to the pathway of starch degradation ( RhBAM3 ) and raffinose family oligosaccharides ( RhGolS2, RhRS2 and RhRS6 ) were up-regulated during cold acclimation. Low temperatures resulted in transient induction of RhBAM3 for 'Dagmar Hastrup' and 'Chandos Beauty', while freezing temperatures further accelerated the expression of RhBAM3 in 'Chandos Beauty'. The up-regulation of RhRS2 is mainly induced by low non-freezing temperatures. Subzero temperatures had a significant role in up-regulating the expression of RhGolS2 and RhRS6 . In summary, more cold-hardy cultivar rapidly acclimated in response to low temperatures. The upregulation of dehydrins ; and starch-to-sugar conversion with induction of key genes [ ß-amylase ( BAM ), raffinose synthase ( RS )and galactinol synthase ( GolS )] are involved in cold acclimation of garden roses. By revealing the underlying biochemical and molecular mechanisms associated with cold hardiness, it can help to screen hardy roses in future breeding programs.