ITEMS FROM THE UNITED KINGDOM


JOHN INNES CENTRE

Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom.


Homoeologous gene silencing in hexaploid wheat. [p. 161]

R. Koebner and G. Xia (Shandong University, PR China).

Many cDNA loci are triplicated in the wheat genome. However, the presence of three homoeologous genomic sequences (one/genome) does not necessarily imply that three independent mRNAs either are transcribed or successfully translated. We have been using single-strand confirmation polymorphism to distinguish the homoeologues of gDNA and cDNA (via RT-PCR) sequences from mapped, single-copy cDNA sequences and have been able to demonstrate that silencing of one of the three copies occurs at a significant frequency (Figure 1). We aim to extend this approach to explore both the extent of, and the existence of any genomic patterning of homoeologous silencing in the hexaploid and tetraploid wheat genomes.

 

Facultative pathogens of cereals. [p. 161]

P. Nicholson, E. Chandler, N. Chapman, R. Draeger, D. Simpson, A. Steed, M. Thomsett, and A. Wilson.

We are continuing our studies of FHB and eyespot with emphasis on the former (not reflected in the publication list below). Resistance in wheat to FHB is being characterized in a number of sources (not Sumai 3) using a trait-dissection approach. Visual disease, yield loss, fungal biomass, and DON mycotoxin accumulation are being determined and data used in QTL studies to identify loci associated with each trait.

In addition, we are developing new diagnostic assays to improve our ability to detect the major Fusarium species involved in FHB in the U.K. and elsewhere. This work includes study of variation within F. graminearum, particularly with respect to lineage and chemotype. We have developed PCR assays that allow chemotypes of isolates to be determined without the need for costly mycotoxin analysis.

Work on eyespot is concentrating upon the identification of DNA markers to Pch1 and Pch2. A cDNA-AFLP approach is being used to identify markers linked to these resistances and provide insight into potential mechanisms underlying the resistance.


Discovering genes for protein quantity and grain hardness by marker-mediated genetic analysis in U.K. winter wheat germ plasm. [p. 161-162]

R. Bradburne, A. Turner, L. Fish, and J. Snape.

In a project funded by the U.K. Home-Grown Cereals Authority (HGCA), we have been identifying and analyzing major genes and QTL-controlling attributes of end-use grain quality, in particular grain texture, protein content, and grain size and shape, using molecular marker-mediated methods of genetic analysis. Three populations were studied: a series of RSLs containing a chromosome 5A recombinant between Avalon (hard, high protein) and Hobbit Sib (soft, low protein) in a Hobbit Sib background, an analogous series of RSLs recombinant at chromosome 5D, and a set of 'Avalon/Hobbit Sib' RILs.

In the Hobbit Sib (Avalon 5D), markers significantly associated with grain hardness were found on the short arm, indicating segregation at the major hardness locus Ha. Additionally, this locus was found also to have a significant effect on grain-protein content, with hard lines having higher intrinsic protein, independent of the grain-texture effect. It is not clear if this is a pleiotropic effect of the Ha locus, but we think it is probably a linked locus. Interval mapping for grain protein content also revealed a significant QTL on the long arm of this chromosome, with Avalon contributing the increasing effect, somewhere near to the location of the vernalization gene Vrn-D1. Results from the Hobbit Sib (Avalon 5A) RSL population indicated that although loci influencing grain-protein concentration and grain hardness were consistent between both years of the study, their effect was not strong enough to give a statistical significance. However, the putative loci on 5A and 5D appear homoeologous.

Results from the 'Avalon/Hobbit Sib' RILs by interval mapping indicated statistically significant QTL for grain-protein content and grain hardness over and above the 5A and 5D effects previously detected using RSLs. QTL on chromosomes 2B and 6B were consistent over 2 years of field trials, with Avalon contributing the increasing effect in both cases. Single-year QTL also were significant on chromosomes 6A (2001 only) and 7A (2002 only), both with Hobbit Sib contributing the increasing effect. QTL mapping by multiple-marker regression indicated significant, year-by-year consistent QTL for hardness on chromosomes 1B (Avalon contributing the increasing effect) and also 5BS/7BS (Hobbit Sib contributing the increasing effect).

 

Publications. [p. 162-163]