Genetic differentiation in cauline-leaf-specific wettability of a rosette-forming perennial Arabidopsis from two contrasting montane habitats.

Background and Aims: An altitudinal gradient of leaf wettability is often observed between and within species. To understand its functional significance, positional variation of leaf surfaces within plants should be taken into account. In rosette-forming plants, rosette leaves are near the ground and their adaxial surfaces are exposed, whereas cauline leaves are lifted from the ground throughout the reproductive season, and their abaxial surfaces are more exposed. Here, we investigated leaf wettability of cauline and rosette leaves of Arabidopsis halleri subsp. gemmifera growing in contrasting montane habitats along an altitudinal gradient at Mt Ibuki, Japan.
Methods: We conducted field investigations and a growth chamber experiment to determine whether field-observed variation in leaf wettability was caused by genetic differentiation. We further performed gene expression analysis of a wax-related gene, i.e. AhgCER1, a homologue of A. thaliana ECERIFERUM1 (CER1) that may be involved in differentiation of leaf wettability. Key
Results: We found cauline-leaf specific genetic differentiation in leaf wettability between contrasting montane habitats. Cauline leaves of semi-alpine plants, especially on abaxial surfaces, were non-wettable. Cauline leaves of low-altitudinal understorey plants were wettable, and rosette leaves were also wettable in both habitats. AhgCER1 expression corresponded to observed leaf wettability patterns. Conclusions: Low wettability of cauline leaves is hypothesized to keep exposed surfaces dry when they are wrapping flowering buds in early spring, and presumably protects flowering buds from frost damage. The genetic system that controls wax content, specifically for cauline leaves, should be involved in the observed genetic differentiation, and AhgCER1 control is a strong candidate for the underlying genetic mechanism.