Natural variation
In a collaborative project with Dr. Magnus Nordborg, USC (Aranzana et al, 2005; Toomajian et al 2005, Zhao et al 2007), we are investigating the molecular variation underlying phenotypic variation in vernalization response. Without vernalization, flowering time is highly variable; some accessions flower early whereas some do not flower at all. Several northern accessions need 12 weeks of cold before they are fully vernalized ( Shindo et al, 2005).
We measured FLC expression during and after vernalization in the accessions and found that while FLC is similarly reduced during the first few weeks of vernalization, the length of cold required to stably maintain FLC silencing on return to the warm differs between accessions.
We propose a model where variation in the quantitative accumulation of epigenetic modifications at FLC contributes to natural variation of vernalization response:
Three phases of vernalization are envisaged: an insensitive phase, a phase where silencing occurs (and histone modifications accumulate), and a phase where FLC is fully silenced. The dashed and solid lines represent the accumulation of epigenetic marks in Edi-0 and Lov-1, respectively. Due to a high initial level and higher accumulation rate, full silencing would be reached after 4 wk of cold in Edi-0 and 10–12 wk of cold in Lov-1. (Shindo et al, 2006).
The fitness consequences of the natural variation in vernalization response are being determined in collaboration with Dr Johanna Schmitt and colleagues from Brown University, Rhode Island, who are conducting common garden experiments in five locations throughout Europe (one of which is on the John Innes Centre field plots).
Current areas of activity
- QTL mapping of genes responsible for variation in vernalization requirement or response in selected F2 populations
- Fine mapping and isolation of candidate genes
- Investigation of the molecular evolution of the genes regulating vernalization response.
