Megagametophyte abnormalities of near-isogenic female partial-sterile soybean mutants (Glycine max; Leguminosae)

Megagametogenesis of soybean, Glycine max (L.) Merr., cultivars Clark and Clark k2, and F1 hybrid of Clark (female parent) crossed with Clark k2 (male parent) were studied using stereo light microscopy and confocal scanning laser microscopy. Reproductive development in Clark and Clark k2 plants was compared to F1 hybrid plants. In mature pods, 6.4% of the ovules of Clark, 8.1% of the ovules of Clark k2, and 41.4% of the ovules of F1 hybrid plants were aborted. This female partial sterility was due to incomplete megagametophyte development: undeveloped polar nuclei—or developed but not in a position for fertilization; increased megagametophyte wall thickness; abnormal shape and/or premature degeneration of synergids and intact synergids throughout the life of the ovule; egg cell not well-developed or absent; and megagametophyte remaining uninucleate. Each of these abnormalities contributed to either lack of double fertilization or early megagametophyte abortion. Electronic Publication     

Method for the mapping of a female partial-sterile locus on a molecular marker linkage map

The female gametophyte is an absolutely essential structure for angiosperm reproduction, and female sterility has been reported in a number of crops. In this paper, a maximum-likelihood method is presented for estimating the position and effect of a female partial-sterile locus in a backcross population using the observed data of dominant or codominant markers. The ML solutions are obtained via Bailey’s method. The process for the estimating of the recombination fractions and the viabilities of female gametes are described, and the variances of the estimates of the parameters are also presented. Application of the method is demonstrated using a set of simulated data. This method circumvents the problems of the traditional mapping methods for female sterile genes which were based on data from seed set or embryo-sac morphology and anatomy.     

Genetic analysis and complementation studies on a number of mutant supernodulating soybean lines

Genetic analysis was done on a number of nitrate tolerant supernodulating (nts) mutant soybean lines. These lines are altered in the autoregulation response, and each was isolated as a separate mutational event following chemical mutagenesis. Crosses were made betweennts lines on a diallel pattern, and each was also crossed usingnts lines as female parent, to wild-type nodulation cultivars. F₁ and F₂ data were analysed from each cross for nodulation type and number. No complementation was noted wherents lines were intercrossed, suggesting that in each line the same gene was affected. Wherents lines were crossed with wild-type cultivars all the F₁ progeny were wild-type, confirming that thenls gene is recessive and, with one exception,nts 1116, all of the F₂ progeny segregated into a 3:1 wild-type to supernodulating phenotype, indicating that a single gene is involved. The hypernodulating linents 1116 gave a 1:1 ratio in its F₂ progeny when crossed with othernts lines. This line behaved as a dominant in the latter crosses. No wild-type segregants were recovered, therefore again no complementation look place. This line may be a leaky mutant with partial autoregulation as its segregation ratios do not fall into any of the obvious patterns.     

Genetic characterization of a leaf margin necrosis mutant in wild annual soybean (Glycine soja)

A leaf margin necrosis mutant was observed in a wild annual soybean (Glycine soja Sieb. & Zucc.) population from South Korea. Genetic studies showed that it was controlled by a single recessive nuclear gene, designatedlmn. TheLmn locus segregated independently of theAp, Dial, Dia3, Idh2, Pgi1 andTi isozyme loci.     

Genetic analysis of a polyembryonic mutant in rye

We have obtained one plant regenerated from rye tissue culture which showed a high percentage of polyembryonic seeds in its progeny. The mutation inducing the development of extra embryos is also influencing erroneous cell division, mitosis and meiosis. The genetic analysis indicated that the aptitude for polyembryonic seed formation is a heritable trait controlled by a dominant gene. However, for expression of the phenotype the female parent should have a specific cytoplasm.     

Genetic and cytological analyses of a partial-female-sterile mutant (PS-1) in soybean (Glycine max; Leguminosae)

Soybean partial-female-sterile mutant 1 (PS-1) was recovered from a gene-tagging study. The objectives were to study the inheritance, linkage, allelism, and certain aspects of the reproductive biology of the PS-1 mutant. For inheritance and linkage tests, PS-1 was crossed to flower color mutant Harosoy-w4 and to chlorophyll-deficient mutant CD-1, also recovered from the gene-tagging study. For allelism tests, reciprocal crosses were made with PS-1 and three other partial-sterile mutants (PS-2, PS-3, and PS-4) recovered from the same gene-tagging study. The PS-1 mutant is inherited in a 3:1 ratio and is a single recessive gene. Linkage results indicated that the gene for partial sterility in PS-1 is not linked either to the w4 locus or to the CD-1 locus. Allelism tests showed that the gene in PS-1 is nonallelic to the gene in PS-2, PS-3, and PS-4. Investigations of developing and mature pollen indicated no differences in morphology, stainability, or fluorescence between normal and partial-sterile genotypes. The PS-1 mutant is completely male fertile. Confocal scanning laser microscopy was used to determine that early embryo abortion in PS-1 is due indirectly to abnormal migration of the fused polar nucleus, which prevented it from being fertilized. Subsequent absence of endosperm development leads directly to abortion of the proembryo.     

Differential sensitivity of nodulation to ethylene in soybean cv. Bragg and a supernodulating mutant

We previously found that the ethylene inhibitor Ag⁺ could overcome the inhibitory effect of nitrate on nodulation of soybean ( Glycine max ) cv. Bragg. The same treatment increased nodulation quantitatively under non-inhibitory conditions, strongly suggesting involvement of ethylene in the control of nodulation in this species. Supernodulation mutants that lack internal autoregulation of nodulation, however, had biosynthesis capacity similar to the wild type. In the present work, the effects of ethylene on nodulation of 'Bragg' and two separate, but allelic, supernodulating mutants ( nts382 and nts1007 ) were compared. The nodulation process appeared much more sensitive than plant growth and development to ethylene, which reduced the number of nodules per plant, but nearly twofold more in the wild type than in the supernodulation mutants. The cause–effect relationship is established by the counteracting effect of Ag⁺ and the fact that the stronger the inhibition by ethylene, the higher the recovery of nodulation ability with the ethylene antagonist. This higher tolerance of or lower sensitivity to ethylene in nts382 persists even under low inoculum dose, where nodule number and mass could be decreased to wild-type levels. Differences between the mutant and the wild type in the triple response test do not appear to support differences in ethylene perception on a whole-plant basis. The results suggest that sensitivity of nodulation to ethylene might have been affected in supernodulation mutants.     

Genetic studies with a phosphoglucose isomerase mutant of Saccharomyces cerevisiae.

Summary A mutation pgi1 in the yeast Saccharomyces cerevisiae conferring deficiency of the glycolytic enzyme glucose 6-phosphate isomerase is characterised genetically. The mutation segregates 2⁺:2^- in tetrads from diploids heterozygous for the mutant phenotype. The mutation is semi-dominant and is located on the right arm of chromosome II in the order: tsm134-lys2-pgi1-tyr1 approximately 15 map units from tyr1. The mutation pgi1 defines the structural gene of glucose 6-phosphate isomerase and can be suppressed intragenically giving revertants that have an unstable enzyme. In one temperature-sensitive revertant no enzyme activity in excess of the mutant level could be detected although fructose 6-phosphate was converted to glucose 6-phosphate in vivo. The suppressor locus in this revertant is dominant and is unlinked to the pgi1 locus.     

Genetic study of a lethal necrosis to soybean mosaic virus in PI 507389 soybean

PI 507389 soybean [Glycine max (L.) Merr.], a large-seeded line from Japan, exhibits a rapid, lethal, necrotic response to strains G1, G2, G5, and G6 of soybean mosaic virus (SMV). Unlike the hypersensitive necrotic reaction, this stem-tip necrosis can be a serious threat to soybean production. To investigate the genetic basis of lethal necrosis (LN), PI 507389 was crossed with the susceptible (S) cv. Lee 68 and with resistant (R) lines PI 96983, cv. York, and cv. Marshall, which carry single dominant genes for SMV resistance at the Rsv1 locus. F(1) plants, F(2) populations, and F(2:3) lines were inoculated with G1 and G6 in the greenhouse or in the field. Results indicated that LN is controlled by a single gene allelic to Rsv1, and this allele in PI 507389 is recessive to R alleles in PI 96983, York, and Marshall. The LN allele is codominant with the allele for S, for the heterozygotes showed a mixed phenotype of both necrosis (N) and mosaic (M) symptoms (NM). The LN allele becomes recessive to the S allele as the mixed NM shifts to S at a later stage in response to more virulent strains. The gene symbol Rsv1-n is assigned for the allele conferring LN in PI 507389. Rsv1-n is the only allele at the Rsv1 locus conditioning N to G1 and no R to any other SMV strains, and thus a unique genotype for SMV strain differentiation. The phenotypic expression of heterozygotes and the dominance relationships among R, N, and S depend on the virulence of SMV strains, source of alleles, and developmental stage.     

Genetic characterization of a filament-forming, lipoprotein-deficient mutant of Escherichia coli.

The fam-715 allele of Escherichia coli ST715, previously described as a temperature-sensitive filament former with reduced levels of lipoprotein at the nonpermissive temperature (S. V. Torti and J. T. Park, Nature [London] 263: 323--326, 1976), was mapped at 74 min. This mutation appears to be amber. It is recessive and can be complemented by F' plasmids carrying the wild-type allele or by an F' plasmid carrying an amber suppressor. Isotopic labeling experiments as well as map position differentiate the fam-715 allele from lipoprotein structural gene mutations.     

Characterization of a non-abscission mutant in Lupinus angustifolius. I. Genetic and structural aspects

A spontaneous mutant, Abs, that does not abscise any organs despite an apparently normal pattern of growth and senescence was isolated from among plants of Lupinus angustifolius cv. 'Danja'. Abs was found to be a recessive single gene mutation, and it was proposed that the gene for the original mutant phenotype, referred to as Abs, be designated abs1. An artificially induced mutant allelic to abs1 was also obtained and a non-allelic mutant phenotype, Delabs (delayed abscission), which was designated abs2. Morphological and cytological features of the abscission process under conditions of natural and ethylene-induced senescence were compared in the wild-type parent and Abs mutant. In the parent genotype abscission under natural conditions is similar to many other species, consisting of a stage of cell division forming an abscission zone, activation of the cytoplasm of zone cells, dissolution of the middle lamella, disorganization of fibrillar wall structure, and cell separation. A slightly different pattern of abscission zone development was observed for ethylene-treated explants of the parent, mainly with respect to features of cell division and cell enlargement. In Abs no abscission occurred for any abscission sites under conditions of natural senescence or with ethylene treatment of small shoot explants. However, relatively normal abscission zones were differentiated at all sites in the mutant except that extensive cell wall disorganization did not occur. Ethylene production by leaves or other organs of the mutant was no different from that of Danja. Application of copper salts or hydrogen peroxide, droughting, waterlogging, or application of abscisic acid (ABA) increased ethylene production equally in both genotypes but did not result in abscission in the mutant. Release of root cap border cells, the only other cell separation process examined, was similar in each genotype. The study concludes that the mutation is quite specific to the abscission process and may be due to a lack of or delay in the expression of hydrolytic enzyme(s) associated specifically with abscission zone differentiation and separation.     

Genetic and experimental studies on a new pigment mutant in Xenopus laevis.

White lethal (wl) is a recessive mutation affecting the differentiation of the three types of chromatophores in Xenopus laevis and eventually leading to the death of the mutants around stage 50. Melanophores appear at st. 33 but differentiate abnormally, remaining pale grey, and do not proliferate after st. 41. The rare xanthophores present contain only a few differentiated pterinosomes, and the iridophores consist of noniridescent white dots. When the albino gene (ap) is combined with wl, melanophores do not differentiate. Reciprocal heterotopic and orthotopic trunk neural crest grafts have shown that the defect is intrinsic to the neural crest cells but is not due, in the case of melanophores, to a tyrosinase deficiency as revealed by the dopa reaction. The mode of action of the gene, the abnormal pattern, and lethality are discussed.     

Genetic mapping of sporulation operons in Bacillus subtilis using a thermosensitive sporulation mutant.

A thermosensitive sporulation mutant was used to determine the order of sporulation operonsin the urs region of the Bacillus subtilis chromosome. Data from three-factor transformation crosses and three- and four-factor transduction crosses established the order metC-SPO-96(SpoII)-spo-85(SpoV)-spo-279(SpoII)-furA-ura-cysC-spo-NG1.67(SpoIII). Previously, furA was thought to lie to the right of ura and cysC to the left (Dubnau, 1970; Young and Wilson, 1972).     

Genetic analysis and characterization of a Caulobacter crescentus mutant defective in membrane biogenesis.

A mutant of Caulobacter crescentus has been isolated which has an auxotrophic requirement for unsaturated fatty acids or biotin for growth on medium containing glucose as the carbon source. This mutant exhibits a pleiotropic phenotype which includes (i) the auxotrophic requirement, (ii) cell death in cultures attempting to grow on glucose in the absence of fatty acids or biotin, and (iii) a major change in the outer membrane protein composition before cell death. This genetic lesion did not appear to affect directly a fatty acid biosynthetic reaction because fatty acid and phospholipid syntheses were found to continue in the absence of supplement. Oleic acid repressed fatty acid biosynthesis and induced fatty acid degradation in the wild-type parent, AE5000 . The mutant strain, AE6000 , was altered in both of these regulatory functions. The AE6000 mutant also showed specific inhibition of the synthesis of outer membrane and flagellar proteins. Total phospholipid, DNA, RNA, and protein syntheses were unaffected. The multiple phenotypes of the AE6000 mutant were found to cosegregate and to map between hclA and lacA on the C. crescentus chromosome. The defect in this mutant appears to be associated with a regulatory function in membrane biogenesis and provides evidence for a direct coordination of membrane protein synthesis and lipid metabolism in C. crescentus.     

Genetic and enzymatic analysis of a glycerol kinase deficient mutant in Neurospora crassa.

Summary Genetic analysis showed that the glycerol non-utilizing isolate gly-u(234) of Neurospora crassa is derived by mutation in a nuclear gene situated in the right arm of linkage group I, about 2.2 crossover units distal to ad-9 and 11 units proximal to nit-1.Enzymatic testings using a radiochemical method indicate that the mutant is deficient for the enzyme glycerol kinase. The radiochemical testings further indicate that the mutation has inactivated an inducible glycerol kinase, while a low residual activity may be due to a second, basal and non-inducible glycerol kinase, in accordance with a proposal by North (1973, 1974) that Neurospora has two glycerol kinases with these properties.     

Genetic and physiologic analysis of a formyl-tetrahydrofolate synthetase mutant of Streptococcus mutans.

Previously we reported that transposon Tn917 mutagenesis of Streptococcus mutans JH1005 yielded an isolate detective in its normal ability to produce a mutacin (P. J. Crowley, J. D. Hillman, and A. S. Bleiweis, abstr. D55, p. 258 in Abstracts of the 95th General Meeting of the American Society for Microbiology 1995, 1995). In this report we describe the recovery of the mutated gene by shotgun cloning. Sequence analysis of insert DNA adjacent to Tn917 revealed homology to the gene encoding formyl-tetrahydrofolate synthetase (Fhs) from both prokaryotic and eukaryotic sources. In many bacteria, Fhs catalyzes the formation of 10-formyl-tetrahydrofolate, which is used directly in purine biosynthesis and formylation of Met-tRNA and indirectly in the biosynthesis of methionine, serine, glycine, and thymine. Analysis of the fhs mutant grown anaerobically in a minimal medium demonstrated that the mutant had an absolute dependency only for adenine, although addition of methionine was necessary for normal growth. Coincidently it was discovered that the mutant was sensitive to acidic pH; it grew more slowly than the parent strain on complex medium at pH 5. Complementation of the mutant with an integration vector harboring a copy of fhs restored its ability to grow in minimal medium and at acidic pH as well as to produce mutacin. This represents the first characterization of Fhs in Streptococcus.     

Phenotypic and genomic analyses of a fast neutron mutant population resource in soybean

Mutagenized populations have become indispensable resources for introducing variation and studying gene function in plant genomics research. In this study, fast neutron (FN) radiation was used to induce deletion mutations in the soybean (Glycine max) genome. Approximately 120,000 soybean seeds were exposed to FN radiation doses of up to 32 Gray units to develop over 23,000 independent M2 lines. Here, we demonstrate the utility of this population for phenotypic screening and associated genomic characterization of striking and agronomically important traits. Plant variation was cataloged for seed composition, maturity, morphology, pigmentation, and nodulation traits. Mutants that showed significant increases or decreases in seed protein and oil content across multiple generations and environments were identified. The application of comparative genomic hybridization (CGH) to lesion-induced mutants for deletion mapping was validated on a midoleate x-ray mutant, M23, with a known FAD2-1A (for fatty acid desaturase) gene deletion. Using CGH, a subset of mutants was characterized, revealing deletion regions and candidate genes associated with phenotypes of interest. Exome resequencing and sequencing of PCR products confirmed FN-induced deletions detected by CGH. Beyond characterization of soybean FN mutants, this study demonstrates the utility of CGH, exome sequence capture, and next-generation sequencing approaches for analyses of mutant plant genomes. We present this FN mutant soybean population as a valuable public resource for future genetic screens and functional genomics research.