Variation of candidate genes related to climate change in European beech ( Fagus sylvatica L.)

European beech (Fagus sylvatica) is an ecologically and economically important tree species in Central Europe. Although beech is a highly competitive species, it does not colonize all habitats in its area of distribution, e.g., very dry habitats. Climate change scenarios predict higher annual mean temperatures and a decrease of precipitation in the summer months. This may increase the drought stress risk in summer and the late frost risk in spring. A candidate gene approach and the analysis of variation within these candidate genes were used in this study to investigate the genetic background of drought stress and bud phenology. Populations along a precipitation gradient in Northern Germany were studied. Additionally, a controlled drought stress experiment was conducted.The neutral genetic diversity analysed with nine microsatellite markers was found to be high for all locations and is comparable to other beech populations. Partial sequences of ten candidate genes were identified at the genomic level and SNPs (Single Nucleotide Polymorphisms) were analysed. The nucleotide diversity range is comparable to other tree species, whereas the mean nucleotide diversity is comparatively low. All populations were found to be significantly different with respect to genetic differentiation.Ten of the seventeen investigated SNPs were found to be significantly different comparing the populations with the highest and the lowest amount of precipitation. The analysis with microsatellite markers showed that these two populations are genetically very different already at neutral markers. Thus, different population histories cannot be ruled out as a reason for the significant differentiation analysing this population pair. In contrast, the populations with the lowest and the middle amount of precipitation are genetically very close, analysed with neutral markers. As expected, only two SNPs were significantly different. These SNPs are from two different genes, isocitrate dehydrogenase and ascorbate peroxidase 4 and are possibly involved in the adaptation to drought stress. Nevertheless, the SNPs found to be different in the comparison of the other population pairs should not be disregarded. The comparison of the damaged and undamaged seedlings from the controlled drought stress experiment revealed that only one SNP in the ascorbate peroxidase 4 gene is significantly different.Although the high neutral genetic diversity is a good basis for adaptation, it is necessary to study the genetic background of climate change related traits to assess the genetic potential to adapt to the changing environmental conditions. The number of analysed candidate genes and SNPs was low in this study, mainly due to the limited available sequences for F. sylvatica. However, it was possible to detect SNPs that are significantly different between the investigated populations and are therefore possibly involved in the adaptation to drought stress. This study is only a first step for the investigation of the genetic background of drought tolerance in the non-model species European beech. In future, the now available next-generation sequencing techniques may be used for further investigation.