Vernalisation of control of blooming in rose
Flowering is a complex process finely regulated by endogenous factors (physiological state, developmental stage, hormones) and environmental cues (photoperiod, light, temperature). Vernalisation, the acquisition of the ability to flower following prolonged cold treatment, has been studied in detail in Arabidopsis and in cereals. In all cases, this process involves changes in the expression of key regulatory genes (e.g. transcription factors or floral repressors/activators), and modification of epigenetic marks, enabling the establishment of a stable flowering response after cold treatment and subsequent return to warm temperatures. The rose represent an original model for studying the effect of cold on flowering in a perennial plant. After winter, axillary buds break dormancy and form stems, following floral initiation and development of an inflorescence. Previous work has highlighted the central role of a flowering repressor, RoKSN (a homologue of Arabidopsis TFL1), in controlling flowering. Our hypothesis is that RoKSN repression is regulated by cold exposure: non-continuously flowering roses (expressing an active RoKSN) require cold to flower, whereas continuous flowering roses (carrying a mutated RoKSN) flower even in absence of cold period. Our objective is to understand the genetic and epigenetic regulation of blooming in response to vernalization in rose. Our current work focuses on a non-continuously flowering rose (R. x wichurana). In the absence of cold, these plants remain dormant. to monitor gene expression during cold accumulation, axillary buds were sampled throughout winter (from September to March). The sampling points included T0 (no cold accumulation) and subsequent stages corresponding to increasing amount of accumulated cold. Cold exposure was quantified in cooling units according to the Q10 method. These samples were subjected to transcriptome (RNA-seq) analysis. For each time point, three potted plants were also transferred from an outdoor condition to greenhouse to estimate the flowering rates. This experiment was repeated over three consecutive years under outdoor conditions.             Regarding flowering rate, all essays were consistent and showed an increase in the number of floral shoot, correlating cold accumulation. In RNA-seq analysis, more differentially expressed genes (DEGs) were detected at the late cold accumulation stage (T140) than at the early stage (T50). Several transcription factors, such as WRKY genes, were differentially regulated only at early stages of cold exposure and may act as potential upstream regulators. In contrast, DAM-related genes (Dormancy-Associated MADS-box) were up-regulated exclusively in dormant buds.