Thermal acclimation in Arabidopsis lyrata: genotypic costs and transcriptional changes.

Frost and heat events can be challenging for sessile organisms that cannot escape thermal extremes. However, adverse effects of thermal stress on fitness may be reduced by pre-exposure to cold or heat, a process known as acclimation. To understand the ecological and evolutionary implications of acclimation, we investigated (1) the reduction in performance due to stress pre-exposure, (2) the magnitude of increased leaf resistance to subsequent stress, (3) the costs of acclimation and (4) the genes differing in expression due to stress pre-exposure. Plants of Arabidopsis lyrata were raised under three treatments of pre-exposure: bouts of frost, bouts of heat or constant temperature. Resistance of leaves to subsequent frost and heat stress was then measured by electrolyte leakage. RNA-seq analysis was performed to examine the genes differentially expressed between stress-pre-exposed and control plants. Pre-exposure to stress during growth decreased plant size and increased leaf resistance to subsequent stress independent of whether pre-exposure was to frost or heat. But the highest increase in leaf resistance to frost was found after pre-exposure to frost (as a trend) and in leaf resistance to heat after pre-exposure to heat. No evidence for costs of acclimation was detected. RNA-sequencing suggested that acclimation by frost and heat pre-exposure was caused by distinct mechanisms: modification of the chloroplast membrane and modification of the cell wall and membrane, respectively. Our results suggest that thermal resistance is a labile complex of traits, strongly affected by the previously experienced stress environment, with undetermined costs.