The elevated protein-bound methionine in maize line BSSS-53 is accounted for by an increase in both the proportion and methionine content of sulfur-rich, low molecular weight proteins (10kD) in the zein-2 fraction (R.L. Phillips and B.A. McClure, Cereal Chem. 62:213-218, 1985). Expression of the major 10kD zein segregates in crosses between inbreds differing in methionine content. We were able to map a gene responsible for overexpression of this high-methionine protein to the short arm of chromosome 4.
Segregation for protein expression was visually detected by isoelectric focusing. Zein-2 was extracted from BC and F2 progeny from crosses between BSSS-53 and W23 waxy translocation and marker stocks. Recombination values of 35.5% and 33.9% were calculated by maximum likelihood from crosses involving wx T4-9g and floury-2, respectively (Tables 1 and 2). An IEF band corresponding in position to Zp22/6 (formerly Zp6) showed complete linkage with the major 10kD band. This would place the gene near Ga1. Preliminary data involving translocations of the long arm of chromosome 4, wx T4-9B, wx T4-9 (5657), further support a gene location on the short arm. Independent segregation was observed in crosses involving opaque-2.
We propose the gene symbol Zpr10/(22) to represent this regulator of the 10kD zein polypeptide with tentative IEF position 22 (H. Hastings, S. Bonanomi, C. Soave, N. Di Fonzo, and F. Salamini, Genet. Agr. 38:447-464, 1984). The overexpression factor may be a unique regulatory gene or a modification of the structural gene.
M.S. Benner and R.L. Phillips
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