Natural variation in Populus tremula flowering time gene PtCO2B

Trees dominate terrestrial ecosystems and produce most of the terrestrial biomass, additionally the increasing worldwide demand for timber, pulp and paper and biofuels means trees are of high economical important, consequently the study of trees is important for both ecological and industrial purposes. Dormancy, bud flush and bud set are important traits both ecologically and for breeding purposes, and forest trees display extensive natural variation in these traits for adaptation to the wide range of climates which they inhabit. The candidate genes PtCO2B and PtCO2A are used in an association mapping approach to investigate the natural variation of these traits. The CONSTANS gene is widely known to be involved in photoperiod responsive pathway of flowering in Arabidopsis, and has recently been shown to be involved in flowering and dormancy in Populus. Here the two Populus homologues of CONSTANS are sequenced within a natural population of Populus tremula collected along a latitudinal gradient. The results show that these genes have less nucleotide diversity than other genes studied in the same population, most of the diversity is found in the single intron and that they have an excess of low frequency mutants. These results suggest that the coding region of these genes is conserved and does not tolerate many mutants. Regression analysis showed that none of the polymorphisms found in PtCO2B were associated with any of the phenotypic traits scores within this population. Future phenotyping within this population may find association with other interesting traits involved in the photoperiod pathway