Research Notes : United States : Monosomics from synaptic KS mutant

Volume 14 Article 41 4-1-1987 Research Notes : United States : Monosomics from synaptic KS mutant Halina Skorupska Iowa State University Reid G. Palmer United States Department of Agriculture Follow this and additional works at: http://lib.dr.iastate.edu/soybeangenetics Part of the Agriculture Commons, Agronomy and Crop Sciences Commons, and the Plant Breeding and Genetics Commons Recommended Citation Skorupska, Halina and Palmer, Reid G. (1987) "Research Notes : United States : Monosomics from synaptic KS mutant," Soybean Genetics Newsletter: Vol. 14 , Article 41. Available at: http://lib.dr.iastate.edu/soybeangenetics/vol14/iss1/41 This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Soybean Genetics Newsletter by an authorized editor of Iowa State University Digital Repository. For more information, please contact . 164 IOWA STATE UNIVERSITY Departments of Agronomy and Genetics UNITED STATES DEPARTMENT OF AGRICULTURE Ames, Iowa 50011 1) New mutations in a genetically unstable line of soybean . Most plants of the Asgrow Mutable line of soybean are chimeric for flower color (Groose and Palmer, 1986). Mutable plants produce both entirely near- white and entirely purple flowers, as well as flowers of mutable phenotype with purple sectors on near-white petals. This line carries an unstable recessive ( ' mutable ' ) allele of the w4 locus that conditions anthocyanin pigmentation (Weigelt et al., 1986). The mutable allele reverts at high frequency from the recessive state to a stable dominant state. Many such mutable alleles in plants have been analyzed at the molecular level and in every instance the action of a transposable element has been established (Doring and Starlinger, 1986). We hypothesize that the Asgrow Mutable line harbors an active transposable element system and that the high frequency of reversion of the unstable allele results from ex cision of the putative element from the w4 locus. The objective of our study was to recover new mutations at other loci in the Asgrow Mutable line as evidence for transposition of a mobile genetic element. We reasoned that the probability of recovering new mutations might be maximized by searching for mutants among progenies of wildtype (germinal revertant) progeny of mutable plants. A germinal revertant is the result of a reversion .of the unstable allele in the germline of a mutable parent. Germinal revertants produce only wildtype purple flowers and their self progenies either breed true for wildtype pigmentation or segregate 3 wildtype : l mutable. If a reversion of the unstable allele is the result of transposition of the positive element out of the w4 locus and into another locus, then new mutations at other loci might be detected among the progenies of germinal revertants . Our strategy was to survey progenies of many germinal revertants (each of which was derived from an independent reversion event) for new mutations at as many loci as possible . A summary of the study is presented in this communication. Three accompanying research notes describe new mutations for chlorophyll deficiency (Groose et al., 1987), partial sterility (Groose and Palmer, 1987) and necrotic roots (Blomgren et al., 1987). Materials and methods : The experiment was conducted as follows : Step 1 : (F 9 generation; Field nursery, Ames, Iowa, 1985) . Two thousand mutable plants were selected from F9 progeny rows that descended from 60 highly mu table F8 plants of the Asgrow Mutable line . Each F9 plant was threshed separately to produce 2000 F 10 families. Step 2: (F 10 generation; Off- season nursery , Puerto Rico, winter 1985- 86). Approximately 30 seed of each of the 2000 F10 families were planted to produce an F 10- progeny r ow. A single germinal revertant was selected from each row that contained at least one germinal revertant (1599 rows) . Selection of a single germinal revertant from each progeny row assured that every germinal revertant was derived from an independent reversion even t. For each row that produced no germinal revertants (401 rows) , a single mutable plant was selected . Selected plants were threshed separately to pr oduce 2000 F 11 families . 165 Step 3 : (F11 gener at i on ; Greenhou se sandbench and field nursery , Ames , Iowa , 198 6) . Sufficient seed was available to test 1936 and 1697 F11 families, res pectively, in a g r eenhouse sandbench and i n a field nursery . In the sandbench , approximately 25 seedlings in each family were observed for segr egation for new mutations until the second trifoliolate leaf stage when plant s were pulled from the bench for examinat ion of root systems . In the field nursery, approximately 25 plants in each family were observed periodically throughou t the season and at maturity for segregation for new mutations . In both locations , progenies were surveyed for characters that are easily evaluated by visual examination. These included chlorophyll pigmentation , root fluorescence , seed pigmentation, leaf form, sterility , dwarfness, stem and petiole morphology, and time of flowering and maturity. Dominant alleles of more than SO described nuclear loci condition the wildtype phenotypes of these trai ts (Palmer and Kilen, 1987) and the Asgrow Mutable line breeds true for wildtype for all these traits. Most new mutations that result from insertion of a transposable element are expected to be recessive. In this experiment, some F10 plants are expected to descend from F9-germline sectors that carry new recessive mutations . Mutant F9-germline sectors are expected to be heterozygous for the new mutations and to produce F10 progeny that segregate 1 homozygous wildtype:2 heterozygous: l homozygous recessive. Therefore, 25%, 50%, and 25%, respectively, of F11 families that descend from F9-germline sectors with new nonlethal recessive mutations are expected to breed true for wildtype, segregate 3 wildtype: l recessive, and breed true for the recessive phenotype. Deleterious mutations are expected to eliminate some homozygous recessive plants , alter segregation ratios, and reduce the probability of recovering F11 families that breed true for recessive mutations. Results: Several new mutations were either true-breeding or segregating in the F11 (Table 1) . Each of these was recovered in a different F11 family. All were derived from germinal revertant F 10 plants and probably descend from mutational events in germline sectors of mutable F9 plants. These mutations are described in more detail in the accompanying research notes. In addition, possible new mutations were recovered as single variant plants in several other F11 families (Table 2). If any of these variant plants is the result of a genetic mutation, the mutational event probably occurred in a germline sector of the F10 parent. Inheritance of these possible new muta t ions is the subject of current research . Discussion: We h (...truncated)