Morphological plasticity and gene expression differences in Arabidopsis thaliana genotypes when grown at ambient and extreme temperatures

Background/Question/Methods

Recent increases in global temperature have been shown to adversely affect the reproductive success of certain plant species. However, it is predicted that plant species exhibiting phenotypic plasticity in flowering traits might be able to tolerate the increased mean annual temperatures. To address this, we tested for phenotypic plasticity in morphological traits for 18 lines of Arabidopsis thaliana collected from widely distributed latitudes (34.43°to 60.23°) by growing individuals within (18°C) and at the limit of (26°C) of their normal growing temperatures. We addressed intraspecific variation in fitness-related traits across temperatures and asked (1) whether the variation seen at ambient temperatures is maintained under higher temperatures, and (2) what the heritability was for different traits across the two temperatures. Our experiment was performed on eight mothers taken from the 18 lines under 16 h long-day conditions. Furthermore, to better understand whether similar genetic mechanisms underpin individual and intraspecific variation in flowering time, we chose five lines that were shown to vary in their flowering time expression at both 18°C and 26°C, and quantified the expression of genes known to be involved in the ambient temperature flowering pathway in the A. thaliana Columbia ecotype (SVP, FLMᵦ and FLM_ᵟ).

Results/Conclusions

Fitness related traits (bolting time, rosette leaf number, rosette diameter, aboveground dry weight, stem length, total fruit production, and seed weight) varied considerably across the 18 A. thaliana lines and across treatments, suggesting plastic responses to temperature. At 18°C, high phenotypic variation resulted in high broad heritability for number of leaves (H²= 0.28), rosette diameter (H²= 0.46), stem length (H²= 0.41), and total number of fruits (H²= 0.52). At 26°C, overall low phenotypic variation resulted in overall lower heritabilities for number of leaves (H²= 0.12), rosette diameter (H²= 0.20), and stem length (H²= 0.27) but did not affect the heritability of total fruits (H²= 0.49). In accordance with the A. thaliana Columbia ecotype, SVP was consistently lower and FLMᵦ higher at 18°C versus 26°C across all five lines. However, the predicted increase of FLM_ᵟ at higher temperatures was only observed for two of five experimental lines. Variation among the three genes expression was evident across populations within each treatment. Together, our results show that potentially stressful high temperatures dampen intraspecific variation and heritability in fitness related traits, A. thaliana shows intraspecific variation in temperature-mediated phenotypic plasticity, and SVP/FLMᵦ expression may be important in the plants plastic response to temperature.