B hordein is a polymorphic mixture of polypeptides that form the major storage protein fraction of barley grain. Studies in several laboratories have shown that it is encoded by a single multigenic locus. Hor2, on the short arm of chromosome 5 (see Shewry and Miflin (1982) and Shewry et al. (1987) for reviews). However, Netsvetaev and Sovinov (1982 have reported that the B hordein polypeptides with fast mobilities on starch gel electrophoresis are controlled by a second locus, HrdF, located about 0.3 cM distally to Hor2. The mapping of HrdF has not been confirmed by other workers, and the structural relationships of the proteins encoded by Hor2 and HrdF are not known. One problem is that Netsvetaev and Sozinov (1982) extracted native hordein fractions (without a reducing agent) and separated them by starch gel electrophoresis, while most other workers analyze total hordein fractions (extracted with a reducing agent) by SDS-PAGE. In order to overcome this Dr. Netsvetaev kindly supplied us with a number of lines with different alleles at the Horl (C hordein), Hor2 and HrdF loci. Six of these (Okessky 46/1 to 46/6) are homozygous lines from a cross between Okessky 17 and Chenad 395. SDS-PAGE patterns of total hordein fractions from these lines and their hordein alleles as designated by Netsvetaev and Sozinov (1982) are shown in Figure 1. Comparison of the patterns of pairs of lines with different alleles at the HrdF but not the Hor2 locus (e.g., 46/1 and 46/2, 46/4 and 46/5) shows differences in the fastest (i.e., low M_r) polypeptides in the B hordein region. These presumably correspond to the products of the HrdF locus.

Although we have previously suggested that HrdF encodes one of the two major subfamilies of B hordein polypeptides identified by structural and molecular analyses (see Shewry et al. 1987), the observations above indicate that this is unlikely. It is more likely that it encodes the minor group of B hordein-related polypeptides called nu-type hordein (Shewry et. al., 1985). These were initially isolated and characterized from Risø 56, which has a deletion mutation at the Hor2 locus that results in absence of all the typical B hordein polypeptides (Doll, 1980; Kreis et. al., 1983). Netsvetaev and Sozinov (1982) reported the presence of proteins encoded by HrdF but not Hor2 in Risø 56. We have also shown that the lowest M_rnu -type hordein band of Risø 56 co-migrates with the HrdF product present in Donetsky 4 (arrowed in Figure 1). This cultivar also has the same B hordein (Hor2) allele as Carlsberg II (the parental cultivar of Risø 56). It is clear, therefore, that at least some of the v- type hordeins are encoded by HrdF. We do not yet know if this applies to the whole group.

Finally, we propose that the designation of HrdF should be changed to Hor5. This follows the system of nomenclature that is generally accepted by workers in North America, Western Europe and Australia.

References:

Doll, H. 1980. A nearly non-functional mutant allele of the storage protein locus Hor2 in barley. Heredity. 93:217-222.

Kreis, M., Shewry, P. R., Forde, B. G., Rahman, S. and Miflin, B. J. 1983. Molecular analysis of a mutation conferring the high-lysine phenotype on the grain of barley (Hordeum vulgare). Cell. 34:161-167.

Netsvetraev, V. P. and Sozinov, A. A. 1982. Linkage studies of genes Glel and HrdF in barley chromosome 5. BGN 12:13-18.

Shewry, P. R. and Miflin, B. J. 1982. Genes for the storage proteins of barley. Qual. Plant Plant Foods Hum. Nutr. 31: 251-267.

Shewry, P. R., Kreis, M., Parmar, S., Lew E. J.-L. and Kasarda, D. D. 1985. Identification of nu -type hordeins in barley. FEBS Lett. 190:61-64.

Shewry, P. R., Williamson, M. S., Parmar, S., Burgess, S. R., Buxton, B. and Kreis, M. 1987. The Biochemical Genetics of barley seed proteins. In Barley Genetics V. Proc. 5th Int. Barley Genet. Symp. Okayama, Japan.