LAUSR

Premise of research. Recent increases in global temperature have been shown to adversely affect the reproductive success of certain plant species. It is predicted that plant taxa exhibiting phenotypic plasticity in flowering traits might be able to tolerate increased mean annual temperatures better than less plastic taxa. However, the underlying genetic and developmental mechanisms for phenotypic plasticity in response to high temperatures are only starting to be elucidated. Methodology. We characterized flowering time plasticity in 14 wild ecotypes of Arabidopsis thaliana under 18°C and 26°C and determined whether alternative splicing of the ambient temperature flowering pathway gene FLOWERING LOCUS-M (FLM) and expression of SHORT VEGETATIVE PHASE (SVP) can explain flowering time plasticity in a subset of these ecotypes. Pivotal results. Our results demonstrate intraspecific variation in A. thaliana temperature-mediated phenotypic plasticity and show that potentially stressful high temperatures do not dampen intraspecific variation in flowering time relative to lower temperatures but do reduce variation across the ecotype means. Although average SVP expression is consistently lower in plants grown at 18°C versus 26°C, the ratio of FLM-β to FLM-δ correlates with flowering time plasticity in only three out of five ecotypes. Furthermore, percentage change in the FLM-β:FLM-δ ratio between temperatures does not explain plasticity in flowering time across all populations. Conclusions. Arabidopsis thaliana ecotypes respond plastically in flowering time to changes in temperature, with higher temperatures causing a general shift toward early flowering. Although SVP and FLM-β expression tracks reaction norms, we failed to find evidence supporting a role for plasticity of alternative FLM splicing in intraspecific flowering time variation when ecotypes of A. thaliana were grown under moderate versus high temperatures. This suggests other, as yet unexplored genetic regulators of high-temperature flowering time plasticity across the natural range of A. thaliana.