Cuticle function can be pivotal to plant success in different environments. Yet, the occurrence of intraspecific adjustments in cuticle traits resulting from acclimation or adaptation to different habitats remains poorly understood. Here, we used genetically well-characterised populations of Arabidopsis arenosa to investigate whether cuticle traits were adjusted as part of the parallel evolution from a foothill to an alpine ecotype. Six alpine and six foothill populations, representing at least three independent evolutionary origins of an alpine ecotype, were used in reciprocal transplantation experiments, to investigate cuticle traits at the eco-physiological, biochemical and structural levels. The genetic basis behind these traits was assessed by combining selection scans and differential gene expression analysis. Overall, alpine populations showed reduced cuticular transpiration in conjunction with consistently altered cuticular wax composition, with higher accumulation of two fatty alcohols and two iso-alkanes. Genomic analysis unravelled nine genes associated with cuticular wax metabolism showing allelic differentiation in alpine compared to lowland populations. In silico gene expression analysis revealed differences between ecotypes for several genes related to cuticle metabolism. Repeated ecotypic differentiation in cuticle traits together with the genetic architecture of the alpine ecotype points at an adaptive value of cuticle adjustments for the colonisation of alpine habitats.

• Keywords
• Alpine habitat, Arabidopsis arenosa, adaptation, cuticle, cuticular wax composition, ecotype, parallel evolution,
• MeSH
• Arabidopsis * genetics   physiology   MeSH
• Ecosystem * MeSH
• Ecotype MeSH
• Plant Epidermis * physiology   genetics   MeSH
• Phenotype MeSH
• Quantitative Trait, Heritable * MeSH
• Plant Leaves * physiology   genetics   anatomy & histology   MeSH
• Gene Expression Regulation, Plant MeSH
• Genes, Plant MeSH
• Waxes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Waxes MeSH

Functional and structural adjustments of plants in response to environmental factors, including those occurring in alpine habitats, can result in transient acclimation, plastic phenotypic adjustments and/or heritable adaptation. To unravel repeatedly selected traits with potential adaptive advantage, we studied parallel (ecotypic) and non-parallel (regional) differentiation in leaf traits in alpine and foothill ecotypes of Arabidopsis arenosa. Leaves of plants from eight alpine and eight foothill populations, representing three independent alpine colonization events in different mountain ranges, were investigated by microscopy techniques after reciprocal transplantation. Most traits clearly differed between the foothill and the alpine ecotype, with plastic adjustments to the local environment. In alpine populations, leaves were thicker, with altered proportions of palisade and spongy parenchyma, and had fewer trichomes, and chloroplasts contained large starch grains with less stacked grana thylakoids compared to foothill populations. Geographical origin had no impact on most traits except for trichome and stomatal density on abaxial leaf surfaces. The strong parallel, heritable ecotypic differentiation in various leaf traits and the absence of regional effects suggests that most of the observed leaf traits are adaptive. These trait shifts may reflect general trends in the adaptation of leaf anatomy associated with the colonization of alpine habitats.

• Keywords
• adaptation, alpine environment, ecotype, leaf anatomy, parallel evolution,
• Publication type
• Journal Article MeSH