Submitted to: Genome
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/31/2007
Publication Date: 2/29/2008
Citation: Palmer, R.G., Zhang, L., Huang, Z., Xu, M. 2008. Allelism and Molecular Mapping of Soybean Necrotic Root Mutants. Genome. 51:243-250. Interpretive Summary: Changes in a plant’s appearance can be due to biotic or abiotic factors and may or may not be heritable. In soybean, some changes or mutations affect root development. A total of 30 necrotic root mutants were identified, some were spontaneous, one was chemically induced, and 24 were the result of mutability. The objective was to determine if all 30 mutants were genetically similar and to locate the mutants on the soybean genetic roadmap. All necrotic root mutants were genetically similar (identical) and mapped to the same location, molecular linkage group G, on the roadmap. These necrotic root mutants mimic Phytophthora root rot, a very devastating disease in soybean. These mutant plants are called disease lesion mimics. These mutant plants are of great interest to plant pathologists who study Phytophthora diseases and to molecular biologists who study the cause of mutations.
Technical Abstract: Mutability of the w4 flower color locus in soybean [Glycine max (L.) Merr.] is conditioned by an allele designated w4-m. Germinal revertants recovered among self-pollinated progeny of mutable plants have been associated with the generation of necrotic root mutations, chlorophyll-deficiency mutations, and sterility mutations. A total of 24 necrotic root mutant lines were generated from a total of 24 independent reversion events at the w4-m locus. The initial mutable population included four mutable categories for w4-m designated; 1) low frequency of early excisions, 2) low frequency of late excisions, 3) high frequency of early excisions, and 4) high frequency of late excisions. These mutable categories were based upon flower phenotype, ie somatic tissue. A total of 22 out of 24 necrotic root mutations occurred from germinal reversions classified in the high frequency of excision category. Of the 22 mutants, 14 came from early excisions and 8 came from late excisions. These necrotic root mutants were allelic to six previously identified necrotic mutants derived from the study of germinal revertants, ie., gene tagging studies; chemical mutagenesis, and ‘spontaneous’ occurrences from genetic crosses. Thus all 30 necrotic root mutants in soybean are allelic. An F2 mapping population from the cross of Minsoy x rn1 rn1 (T328) was used to map the Rn1 locus using simple sequence repeat (SSR) markers. The Rn1 locus was located between Satt288 and Satt612 on molecular linkage group G.