Plant Genome IV Conference Plant Genome IV Conference
Zeins, the storage proteins in maize, constitute 50-60% of the total protein in mature seeds and determine the nutritional quality of kernels. They are expressed in the endosperm, under strict developmental control. The gene dzr1 (delta-zein regulator) encodes for a trans-regulator responsible for the overexpression of the high-methionine 10-kDa d-Zein in the maize inbred BSSS53. dzr1 shows allele-specific parental imprinting and is tightly linked to a cluster embodying all the genes and pseudogenes for the 22-kDa a-zeins. The cluster has a maximum size of 200-250 kb and spans 3.4 cM in chromosome 4S [S. Chaudhuri and J. Messing, Proc. Natl. Acad. Sci. USA, 91, 4867 (1994); S. Chaudhuri and J. Messing, Mol. Gen. Genet., 246, 707 (1995)]. As part of our initial approach to isolate and characterize dzr1, we are constructing the complete physical map of the 22-kDa a-zein region. We have made a long range restriction map of the region using high-molecular-weight DNA techniques. We have estimated that there are 16-18 genes and other related sequences (i.e., pseudogenes) for the 22-kDa alpha-zeins distributed in two subclusters. We have constructed an overlapping, 8-genome equivalent BSSS53 cosmid library. Thus far, we have subcloned and sequenced 14 different zein genes and created cosmid overlaps covering most of the region. Characterizing dzr1 and the physical organization of the 22-kDa a-zein cluster will help our understanding of plant genome evolution, imprinting and regulation of zein accumulation and may result in novel approaches to increase nutritional value of maize.