Conservative flowering behaviours, such as flowering during long days in summer or late flowering at a high leaf number, are often proposed to protect against variable winter and spring temperatures which lead to frost damage if premature flowering occurs. Yet, due the many factors in natural environments relative to the number of individuals compared, assessing which climate characteristics drive these flowering traits has been difficult. We applied a multidisciplinary approach to 10 winter‐annual Arabidopsis thaliana populations from a wide climactic gradient in Norway. We used a variable reduction strategy to assess which of 100 climate descriptors from their home sites correlated most to their flowering behaviours when tested for responsiveness to photoperiod after saturation of vernalization; then, assessed sequence variation of 19 known environmental‐response flowering genes. Photoperiod responsiveness inversely correlated with interannual variation in timing of growing season onset. Time to flowering appeared driven by growing season length, curtailed by cold fall temperatures. The distribution of FLM, TFL2 and HOS1 haplotypes, genes involved in ambient temperature response, correlated with growing‐season climate. We show that long‐day responsiveness and late flowering may be driven not by risk of spring frosts, but by growing season temperature and length, perhaps to opportunistically maximize growth.

The external cues that trigger timely flowering vary greatly across tropical and temperate plant taxa, the latter relying on predictable seasonal fluctuations in temperature and photoperiod. In the grass family (Poaceae) for example, species of the subfamily Pooideae have become specialists of the northern temperate hemisphere, setting up the hypothesis that their progenitor evolved a flowering response to long-days from a short-day or day-neutral ancestor. Sampling across the Pooideae, we found support for this hypothesis, and identified several secondary shifts to day-neutral flowering and one to short-day flowering in a tropical highland clade. To explain the proximate mechanisms for the secondary transition back to short-day-regulated flowering, we investigated the expression of CCT domain genes, some of which are known to repress flowering in cereal grasses under specific photoperiods. We found a shift in CONSTANS 1 and CONSTANS 9 expression that coincides with the derived short-day photoperiodism of our exemplar species Nassella pubiflora. This sets up the testable hypothesis that trans- or cis-regulatory elements of these CCT domain genes were the targets of selection for major niche shifts in Pooideae grasses.

Enset (Enseteventricosum (Welw.) Cheesman) is a multipurpose, drought-tolerant and a key food security crop, which is the staple food for peoples in the South and Southwestern parts of Ethiopia. Despite its importance, enset is an orphan crop as regards genetic research and breeding. In this study, we characterized genetic diversity, population structure and selection signatures in 226 cultivated and 10 wild enset accessions collected from diverse enset growing regions of Ethiopia using 3505 high-quality SNP markers obtained from ddRAD-sequences. The population structure and cluster analyses clearly distinguished between cultivated and wild enset. AMOVA revealed much higher levels of genetic variation within populations and regions (91.2 and 92.4%, respectively) than between populations and regions (8.8 and 7.6%, respectively). This shows that the region of origin and environmental heterogeneity have little influence on the genetic variation. However, the genetic differentiation between regions was moderate to large (FST = 0.06–0.17). The genetic structure of enset was mainly shaped by eco-geographic factors, mode of propagation and cultivation status. Six genes potentially involved in sexual reproduction and flowering signalling, which are key processes underlying domestication and adaptation, were under positive selection demonstrating that sexual reproduction plays an important role in shaping enset diversity. A lot of unexplored diversity is available for improving enset in Ethiopia, with patterns of diversity consistent with divergent selection on adaptive traits. This diversity also shows potential for introducing enset as a more food secure crop for the food insecure regions in the dry north of Ethiopia.

Conservative flowering behaviors, such as flowering during long days in summer or late flowering at a high leaf number, are often proposed to protect against variable winter and spring temperatures which lead to frost damage if premature flowering occurs. Yet, due the many factors in natural environments relative to the number of individuals compared, assessing which climate characteristics drive these flowering traits has been difficult. We applied a multidisciplinary approach to ten winter-annual Arabidopsis thaliana populations originating along a wide climactic gradient in Norway. We paired a variable reduction strategy to assess which of 100 climate descriptors from their home sites correlated most to their behaviors when grown in common garden and assessed sequence variation of 19 known environmental-response flowering genes. We show that long-day sensitivity and late flowering may be driven not by risk of spring frosts, but by growing season temperature and length perhaps to opportunistically maximize growth.

Conservative flowering behaviors, such as flowering during long days in summer or late flowering at a high leaf number, are often proposed to protect against variable winter and spring temperatures which lead to frost damage if premature flowering occurs. Yet, due the many factors in natural environments relative to the number of individuals compared, assessing which climate characteristics drive these flowering traits has been difficult. We applied a multidisciplinary approach to ten winter-annual Arabidopsis thaliana populations originating along a wide climactic gradient in Norway. We used a variable reduction strategy to assess which of 100 climate descriptors from their home sites correlated most to their behaviors when grown in common garden and assessed sequence variation of 19 known environmental-response flowering genes. Photoperiod sensitivity inversely correlated with interannual variation in timing of growing season onset (start of favorable spring temperatures). Time to flowering appeared driven by growing season length, curtailed by cold fall temperatures. The distribution of FLM, TFL2, and HOS1 haplotypes, genes involved in ambient temperature response, correlated with growing-season climate. We show that long-day sensitivity and late flowering may be driven not by risk of spring frosts, but by growing season temperature and length perhaps to opportunistically maximize growth.