Masoumeh Khodaverdi1, Marian Shubert2, Siri Fjellheim2, Jill Preston1
1Department of Plant Biology, University of Vermont, Burlington, Vermont 05405, USA 2Department of Plant Sciences, Norwegian University of Life Sciences, Ås 1430, Norway
Flowering earlier in response to cold temperatures is referred to as vernalization. This trait has evolved several times independently across angiosperms to adapt the reproduction process of plants to relatively colder temperatures and shorter growing seasons of temperate habitats in comparison to tropical regions, where many Pooideae (Poaceae) have originated from. Based on the previous studies, this process has evolved in the early divergent tribes of Pooideae, implying that vernalization is required for Meliaceae species. Besides that, there is not enough data to conclude whether the underlying mechanisms for vernalization-induced flowering are different or similar at narrower levels (e.g., species-level) in Meliaceae species. To test the hypothesis that vernalization responsiveness has evolved in the early divergent tribes of Pooideae and test the genetic mechanisms of their early acquisition of cold, we conducted a series of experiments on 29 species from Melica L. (Meliceae) collected from broad climatic regions to study how flowering time changes in connection to a gradient of temperatures. In these experiments, we carefully measured the flowering time of different groups of plants that were exposed to various lengths of cold periods as an indication of their sensitivity to vernalization and also compared them to the control group (no cold period). We then quantified the association between their vernalization sensitivity and several environmental factors including latitude and climate indicators, such as temperature and precipitation. Our results demonstrate that vernalization-induced flowering time is widespread within the Melica species and that local adaptation plays an important role in this pathway. Moreover, using comparative transcriptome analysis, we found that differential gene expressions in species that are sensitive to vernalization are mostly distinct from those in non-sensitive species, though there also existed a descent overlap.
Keywords: Vernalization, Pooideae, Melica, Flowering time, Transcriptome analysis