Natural variation in vernalization response of Arabidopsis accessions

The Dean laboratory is investigating the molecular control of flowering. We use the excellent genetic system of Arabidopsis thaliana as it is easy to clone genes controlling many processes based only on having a mutation (a lesion in the gene). We have focused on why and how prolonged cold influences flowering, a process called vernalization. In nature, plants experience prolonged cold during winter and many plants do not flower until they have experienced this prolonged cold. This is an adaptation to ensure flowering in spring when conditions are favourable for maximal flower production and seed set. Many genes controlling this process have now been cloned so in this proposal we want to investigate how their function has changed during adaptation of Arabidopsis to different climates. We are working with Arabidopsis accessions collected from a range of latitudes that extend up to the edge of the Arctic Circle. These plants need much longer periods of cold to accelerate flowering than ones collected from the UK. We have made crosses between these different plants and have analysed the flowering and vernalization response of their progeny. This has indicated that the natural variation in vernalization is the result of allelic variation of 4-5 genes. We now want to identify which genes these are, understand what changes have occurred and how those affect the flowering behaviour. In collaboration with experts in population and ecological genetics, we also want to determine if those changes have spread in the worldwide Arabidopsis population and understand how much advantage those changes confer to the plants in the different environmental conditions.

To get an insight into the molecular basis of adaptation the Dean lab is studying natural variation in flowering time in Arabidopsis accessions. Arabidopsis thaliana plants collected from a range of latitudes extending up to the Arctic Circle have been analysed for their flowering time and vernalization response - the acceleration of flowering by an extended period of cold. The Arabidopsis thaliana accessions were found to need different periods of cold - between 2 to 14 weeks, to satisfy the vernalization requirement. A QTL analysis had indicated that this variation was caused by a small number of genes. The aims of this grant are to identify those genes, define the molecular variation causing the changed flowering response and determine how that changes the phenotype. In collaboration with Dr Magnus Nordborg, a population geneticist from U. S. California we will analyse the molecular evolution of those loci and address whether specific allelic variation is found in a range of accessions collected from different latitudes with common winters or whether variation has arisen independently to allow adaptation in each region. We also want to understand how that variation has been selected by measuring the fitness benefit the allele confers in different environments. This will be achieved as part of an ongoing NSF project, headed by Prof. J. Schmitt (Brown University R.I.) focused on an ecological genetic analysis of >300 Arabidopsis accessions in five European sites.