Natural variation in stomata size contributes to the local adaptation of water-use efficiency in Arabidopsis thaliana

Abstract

A b s t r a c t Stomata control gas exchanges between the plant and the atmosphere. How natural variation in stomata size and density contributes to resolve trade-offs between carbon uptake and water-loss in response to local climatic variation is not yet understood. We developed an automated confocal microscopy approach to characterize natural genetic variation in stomatal patterning in 330 fully-sequenced Arabidopsis thaliana ecotypes collected throughout the European range of the species. We compared this to variation in water-use efficiency, measured as carbon isotope discrimination (δ 13 C). Combined with public genomic and environmental resources, we show that genetic variation for stomata size and density is pervasive in Arabidopsis thaliana. A positive correlation between stomata size and δ 13 C further shows that this variation has consequences on water-use efficiency. Genome-wide association analyses reveal that many loci of small effect contribute not only to variation in stomata patterning but also to its co-variation with carbon uptake parameters. Yet, we report two novel QTL affecting δ 13 C independently of stomata patterning. This suggests that, in A. thaliana, both morphological and physiological variants contribute to genetic variance in water-use efficiency. Patterns of regional differentiation and co-variation with climatic parameters indicate that natural selection has contributed to shape some of this variation, especially in Southern Sweden, where water availability is comparatively more limited in Spring.

Pre-adaptation to climate change through topography-driven evolution of traits and their plasticity

“…In the face of uncertain climate and soil moisture changes, the topographical complexity of mountainous landscapes may harbor an invaluable source of variation in drought resistance traits, including increased water use efficiency (e.g. through more and smaller stomata, Dittberner et al 2018), lower specific leaf area (SLA, Bansal et al 2015) and advanced flowering (Wilczek et al 2010). In this regard, south-oriented slopes are assumed to be dominated by drought-resistant phenotypes, especially where strong inclinations facilitate water efflux.…”

Competition-by-drought interactions change phenotypic plasticity and the direction of selection on Arabidopsis traits

“…Here we show selection among natural genotypes under drought. In nature, the heterogeneity of competition may select for alternate Arabidopsis traits in water limited environments, suggesting a potential mechanism promoting their high genetic diversity in drought responses (Dittberner et al, 2018;Exposito-Alonso et al, 2018). 535…”

“…First, it exhibits substantial diversity in drought 60 response within populations. Studies of genetic variation in δ 13 C, a proxy for water use efficiency (WUE), and stomata have found statistically significant but weak relationships with climate of origin (Dittberner et al, 2018) as have studies of survival (Exposito-Alonso et al, 2018). These weak relationships may be surprising given the tendency for local adaptation in Arabidopsis populations (Fournier-Level et al, 2011) and stand in contrast with cold tolerance, 65 which is more closely tied to local winter temperatures (Ågren & Schemske, 2012;Monroe et al, 2016;Gienapp et al, 2017).…”

“…Some published data suggest the potential for competition-by-climate interaction effects on 70 performance (Baron et al, 2015;Campitelli et al, 2016) though the physiological basis of these interactions is largely unknown. Third, previous research has yielded insight into genetic and physiological mechanisms of drought adaptation, providing a basis for specific hypotheses about how moisture and competitive gradients interact to select for different traits (McKay et al, 2003;Juenger et al, 2010;Des Marais et al, 2012;Lovell et al, 2013;Kenney et al, 2014;Lasky et 75 al., 2014Lasky et 75 al., , 2018El-Soda et al, 2015;Bac-Molenaar et al, 2016;Dittberner et al, 2018;Exposito-Alonso et al, 2018DeLeo et al, 2019).…”

Trait plasticity and covariance along a continuous soil moisture gradient

“…Quantitative genetic variation in myriad drought resistance traits have been observed in natural populations and laboratory model systems. In particular, natural populations of Brassicaceae species (including Arabidopsis thaliana) and Brachypodium harbor variation both constitutive and inducible traits mediating plant-water relations, including water use efficiency (Des Marais et al 2012Marais et al , 2017Edwards et al 2012;Greenham et al 2017), leaf chemistry (Kesari et al 2012;Des Marais et al 2017), leaf anatomy (Skirycz et al 2011;Verelst et al 2013;Dittberner et al 2018), rootshoot biomass partitioning (Des Marais et al 2012Marais et al , 2017, and many others (Verslues and Juenger 2011;Edwards et al 2012;Juenger 2013;Luo et al 2016;Yarkhunova et al 2016;Lenk et al 2019). Among the numerous plant traits that can and have been measured, few have been studied more extensively than specific leaf area (SLA -often reported as it's inverse, leaf mass per area or LMA).…”