Genetic analyses of a putative Mutator-induced deletion involving the blue fluorescent1 (bf1) and brown midrib4 (bm4) loci in maize

A putative Mutator-induced alteration (isolate) involving the blue fluorescent1 (Bf1) and the brown midrib4 (bm4) loci is described. This isolate (Bf1-Mu-044-4) was one of the blue fluorescent1 mutants in a large experiment designed to produce Mutator-induced mutations involving this locus. Evidence is presented supporting the conclusion that this alteration deletes all or part of both the bf1 and bm4 loci. The isolate is infrequently transmitted through the pollen, but is more readily transmitted through the egg, although at less than the expected frequency of 50% for a simple mutation. Heterozygotes of this isolate with the bm4-R allele have brown midribs. These brown midrib plants are shorter than homozygous bm4-R plants and approximately 50% of these Bf1-Mu-044-4/bm4-R heterozygotes do not reach maturity. One putative Mutator-induced bm4 mutation, which occurred in the course of the analysis of the Bf1-Mu-044 isolate, is described. Key words : Mutator, deletion, bf1-bm4 loci.

A transposable element in diverse corn lines, Ubiquitous (Uq): allelism test

Since the discovery of the Uq transposable element system in the early 1980s, studies of Uq distribution have shown that Uq is pervasive in genetic stocks and corn populations including BSSS, the Illinois oil and protein lines, 'Lancaster', 'Jarvis' and several others. The assumption made was that Uq might have provided the variation that has contributed to maize breeding progress. Of the several inbreds tested in previous studies, only IaI159, one of the contributors to BSSS, contained an active Uq. The main question posed in our experiments was that of chromosomal location(s), or allelic relationships, of active Uq elements in diverse corn populations. Results showed that these Uq elements are allelic, linked or independent, though most found from corn populations show quite distant or independent linkage relationships with each other. The lack of a linear linkage map among these Uq elements may be interpreted to have resulted from transposition events and this might have led to the differentiated instability of an individual Uq element that was found to be variable. Other questions also discussed relate to the origin of Uq elements in corn populations and their role(s) in plant breeding.

Complex duplications in maize lines

Rp1 is a disease resistance complex and is the terminal morphological marker on the short arm of maize chromosome 10. Several restriction fragment length polymorphisms (RFLPs), which map within 5 map units of Rp1, were examined to determine if they are also complex in structure. Two RFLP loci, which mapped distally to Rp1, BNL3.04 and PIO200075, existed in a single copy in all maize lines examined. These two loci cosegregated perfectly in 130 test cross progeny. Two RFLP loci that map proximally to Rp1 had unusual structures, which have not yet been reported for maize RFLPs; the loci were complex, with variable numbers of copies in different maize lines. One of the loci, NP1285, occasionally recombined in meiosis to yield changes in the number of copies of sequences homologous to the probe. The other proximal locus, detected by the probes NPI422, KSU3, and KSU4, was relatively stable in meiosis and no changes in the number of restriction fragments were observed. The similarity in map position between Rp1 and the complex RFLP loci indicate there may be genomic areas where variable numbers of repeated sequences are common. The structure of these complex loci may provide insight into the structure and evolution of Rp1.