Role of phenotypic and transcriptomic plasticity in alpine adaptation of Arabidopsis arenosa

Plasticity is an important component of the response of organism to environmental changes, but whether plasticity facilitates adaptation is still largely debated. Using transcriptomic and phenotypic data, we explored the evolution of ancestral plasticity during alpine colonization in Arabidopsis arenosa. We leveraged naturally replicated adaptation in four distinct mountain regions in Central Europe. We sampled seeds from ancestral foothill and independently formed alpine populations in each region and raised them in growth chambers under conditions approximating their natural environments. We gathered RNA-seq and genetic data of 48 and 63 plants and scored vegetative and flowering traits in 203 and 272 plants respectively. Then, we compared gene expression and trait values over two treatments differing in temperature and irradiance and elevations of origin and quantified the extent of ancestral and derived plasticity. At the transcriptomic level, initial plastic changes tended to be more reinforced than reversed in adapted alpine populations. Genes showing reinforcement were involved in the stress response, developmental processes and morphogenesis and those undergoing reversion were related to the stress response (light and biotic stress). At the phenotypic level, initial plastic changes in all but one trait were also reinforced supporting a facilitating role of phenotypic plasticity during colonization of an alpine environment. Our results contrasted with previous studies that showed generally higher reversion than reinforcement and supported the idea that ancestral plasticity tends to be reinforced in the context of alpine adaptation. However, plasticity may also be the source of potential maladaptation, especially at the transcriptomic level.