New isozyme systems for maize (Zea mays L.): Aconitate hydratase,adenylate kinase,NADH dehydrogenase,and shikimate dehydrogenase

Electrophoretic variation and inheritance of four novel enzyme systems were studied in maize (Zea mays L.). A minimum of 10 genetic loci collectively encodes isozymes of aconitate hydratase (ACO; EC 4.2.1.3.), adenylate kinase (ADK; EC 2.7.4.3), NADH dehydrogenase (DIA; EC 1.6.99.—), and shikimate dehydrogenase (SAD; EC 1.1.1.25). At least four loci are responsible for the genetic control of ACO. Genetic data for two of the encoding loci,Aco1 andAco4, demonstrated that at least two maize ACOs are active as monomers. Analysis of organellar preparations suggests that ACO1 and ACO4 are localized in the cytosolic and mitochondrial subcellular fractions, respectively. Maize ADK is encoded by a single nuclear locus,Adk1, governing monomeric enzymes that are located in the chloroplasts. Two cytosolic and two mitochondrial forms of DIA were electrophoretically resolved. Segregation analyses demonstrated that the two cytosolic isozymes are controlled by separate loci,Dia1 andDia2, coding for products that are functional as monomers (DIA1) and dimers (DIA2). The major isozyme of SAD is apparently cytosolic, although an additional faintly staining plastid form may be present. Alleles atSad1 are each associated with two bands that cosegregate in controlled crosses. Linkage analyses and crosses with B-A translocation stocks were effective in determining the map locations of six loci, including the previously described but unmapped locusAcp4. Several of these loci were localized to sparsely mapped regions of the genome.Dia2 andAcp4 were placed on the distal portion of the long arm of chromosome 1, 12.6 map units apart.Dia1 was localized to chromosome 2, 22.2 centimorgans (cM) fromB1. Aco1 was mapped to chromosome 4, 6.2 cM fromsu1. Adk1 was placed on the poorly marked short arm of chromosome 6, 8.1 map units fromrgd1. Less than 1% recombination was observed betweenGlu1 (on chromosome 10) andSad1. In contrast to many other maize isozyme systems, there was little evidence of gene duplication or of parallel linkage relationships for these allozyme loci. This work was supported by grants from Pioneer Hi-Bred International, Inc., of Johnston, Iowa, the National Institute of Health (Research Grant GM11546), and the United States Department of Agriculture (Competitive Research Grant 83-CRCR-1-1273). This is Paper No. 11372 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh.