Genome-Wide Association Study in European Beech (Fagus sylvatica L.) for Drought Stress Related Traits

Genome-wide association studies (GWAS) aim to identify loci associated with different traits, which could be evaluated in subsequent studies and later be prioritized in individual and seed stand selection. In trees, traits are measured at maturity or are only available after a long time, and juvenile-mature correlations are often unknown. Therefore, it is a promising approach to study natural populations directly. Data were collected from approximately 100 adult beech trees per stand in five locations in the Postăvarul Massif, South-Eastern Romanian Carpathians (Carpații de Curbură) along an altitudinal gradient associated with precipitation and temperature. We performed GWAS on 610,678 single-nucleotide polymorphisms (SNPs) using PLINK and Genome-wide Efficient Mixed Model Association (GEMMA) to identify SNP markers associated with drought-stress-related traits. Even though this study used a natural population, we found very interesting associations while accounting for environmental heterogeneity along the altitudinal gradient. A total of 88 markers were associated with stomatal density. Seventy-two markers are located on chromosome 10 in a region spreading from ~5.48 to 13.67 Mb. We found five gene annotations in this region that are thought to play a role in controlling stomatal density in Arabidopsis. All markers within this region exhibit similar allele frequencies, which indicate a connection to stomatal density and the altitudinal gradient. This entire region may be under joint selection for stomatal features. Our research provides insights into the genetic architecture of various drought-stress traits in the studied population.