Gene Copy Number Effect on the Vernalization-HI (VRN-HI) Induced Silencing of CBF Expression in Barley
Dobbins, Cassandra M.
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C-Repeat Binding Factors (CBFs) are generally highly expressed in winter type barley. However, recent findings indicate that winter genotypes exhibit decreased CBF expression after vernalization, a period of prolonged exposure to cold, nonfreezing temperatures when a plant cold acclimates. CBFs are located on the long arm of chromosome 5 at the Frost Resistance-H2 (FR-H2) locus, on which Vernalization-HI (VRN-HI) has repressive effects. In winter barley such duplications have been identified in the CBF2A-CBF4B genomic region at the FR-H210cus. Multiple tandem duplication events have been associated with gene silencing. It may be that multiple CBF copy numbers effectively induce their own silencing. Offspring from a winter, 'Nure,' and a spring type, 'Tremois,' barley cross were used to test this hypothesis. The selected 'Nure' x 'Tremois' (NT) recombinant genotypes carry the N allele at the VRN-HI and VRN-H2 loci, and either the N or T allele at FR-H2. Each gentoype was grown under long day (LD) and short day (SD) photoperiods and plant material harvests were conducted under cold and warm conditions. Northern blot hybridizations were performed for each sample with data from using samples harvested after four weeks of growth and utilized CBF2A and actin probes. Actin was used as a control to normalize CBF2A phosphor autoradiogram signal intensities. CBF2A expression was greatest for both the multiple and single copy allele groups under cold harvest conditions and short day photoperiod. On average, CBF2A was . expressed more in single copy than in multiple copy allele groups under the same conditions; however, a statistically significant difference was observed between multiple and single copy number allele groups under cold harvest conditions and short day photoperiod only.