The genetic control of cadmium levels in tetraploid and hexaploid wheat.
Cadmium (Cd) is a toxic heavy metal, and a significant proportion of dietary Cd intake comes from cereal products. Grain quality surveys have consistently found higher levels of Cd in tetraploid durum wheat (Triticum durum) than in hexaploid bread wheat (T. aestivum), although there is variation within both species. At NIAB we are intercrossing a range of tetraploids with bread wheat, through resynthesis and direct crossing, as part of WISP, the BBSRC public-good wheat pre-breeding programme (http://www.wheatisp.org). Through this, we may be inadvertently moving high-Cd accumulation alleles from tetraploids into bread wheat.
Wholegrain flour samples from field-grown tetraploid and hexaploid WISP materials will be tested to determine actual Cd levels, backed up by genetic analysis of the Cdu1 locus. This was mapped to a 0.7cM interval on 5BL in a segregating durum wheat population, where it explained 82% of the phenotypic variation in Cd accumulation. This interval corresponds to a relatively small region (approx. 285 kbp) in both rice and brachypodium, so the development of diagnostic markers suitable for high-throughput genotyping should be possible. Once developed, these can be then used to routinely select against high-Cd accumulation in parental material and segregating crosses.
Cadmium accumulation may also be a suitable phenotype for exploring changes in gene expression during polyploidisation. For example, would a hexaploid derived from a high-Cd tetraploid necessarily accumulate the same levels as its tetraploid progenitor? How do the (presumably non-functional) homoeologues on 5A and 5D interact with Cdu1?
- Wiebe et al., 2010. Theor Appl Genet 121:1047-1058 http://www.niab.com/uploads/files/NIAB_Synthetic_Hexaploid_Wheat.pdf