Hordein-gene expression during development of the barley (Hordeum vulgare) endosperm.

A previous study [Rahman, Shewry & Miflin (1982) J. Exp. Bot. 33, 717-728] showed differential accumulation of the major storage proteins (called B and C hordeins) in developing endosperms of barley (Hordeum vulgare). To determine how this accumulation is regulated, we have studied mRNA fractions prepared from similar endosperms. Hordein-related mRNA species were detected some days before the deposition of hordeins in vivo. The translation products in vivo directed by polyribosomes, polysomal RNA and total cellular RNA showed similar changes in the proportions of the hordein products to those observed in the accumulations of the proteins in vivo. There was a relative increase in one of the subfamilies of B hordeins (called B1 hordein) and a decrease in the second subfamily of B hordeins (B3 hordein) and in C hordeins. The populations of RNA species related to these three groups of hordeins were studied by 'dot hybridization', with specific complementary-DNA probes for B1-, B3- and C-hordein-related sequences. This showed a 10-15-fold increase in sequences related to the B1 hordein during endosperm development, but only a 4-fold increase in sequences related to B3 and C hordeins. These results indicate that the rates of synthesis of hordeins are related to the abundance of their respective mRNA species. The different results observed for the two subfamilies of B hordeins are of interest, since they indicate differential expression of two subfamilies of genes present at a single multigenic locus.