Partial Sterility Research Articles

Cytological relationships among Eumelilotus species analysed using cytological observations of interspecific hybrids obtained by in vitro culture

Interspecific hybrid plants between Melilotus altissima (yellow flowers) and either M. alba (white flowers) or M. taurica (white flowers) and between M. suaveolens (yellow flowers) and M. wolgica (white flowers) which were inviable because of heavy chlorosis, were grown successfully by in vitro culture and reached the flowering stage. Pollen fertility of hybrid plants between M. altissima and M. alba was about 46% whereas hybrids between M. altissima and M. taurica and between M. suaveolens and M. wolgica showed about 25% and 18% of pollen fertility, respectively. All F1s did not set any selfed seeds. Observing the pairing of chromosomes at metaphase I in the hybrid plants, it was revealed that the genomes of M. altissima and M. alba differ by a reciprocal translocation. This result could account for the partial sterility of pollen in the F1 hybrids. On the other hand, hybrid plants between M. altissima and M. taurica and between M. suaveolens and M. wolgica showed normal pairing of chromosomes though pollen fertility of the hybrids was very low, suggesting that low pollen fertility was controlled by sterility gene(s). These results demonstrate that M. altissima and 7 other species of the subgenus Eumelilotus share the same chromosomal constitution. The only exception, M. alba, differs from the other 8 species by a segmental interchange.

A genome-wide analysis of wide compatibility in rice and the precise location of the S5 locus in the molecular map

The discovery of wide-compatibility varieties (WCVs) that are able to produce normal fertility hybrids when crossed both to indica and japonica rice has enabled the fertility barrier between indica and japonica subspecies to be broken and provided the possibility of developing inter-subspecific hybrids in rice breeding programs. However, a considerable variation in the fertility level of hybrids from the same WCV crossed to different varieties has often been observed. One hypothesis for this variable fertility is that additional genes are involved in hybrid fertility besides the wide-compatibility gene (WCG). To assess such a possibility, we performed a genome-wide analysis by assaying a large population from a three-way cross ‘02428’/‘Nanjing 11’//‘Balilla’ using a total of 171 RFLP probes detecting 191 polymorphic loci distributed throughout the entire rice linkage map. Our analysis recovered 3 loci conferring significant effects on hybrid fertility. The major locus on chromosome 6 coincided in chromosomal location with the previously identified S 5 locus, and the 2 minor loci that mapped to chromosomes 2 and 12, respectively, were apparently distinct from all previously reported hybrid sterility genes. Interaction between the indica and japonica alleles at each of the loci caused a reduction in hybrid fertility. The joint effect of the 2 minor loci could lead to partial sterility even in the presence of the WCG. The location of the S 5 locus on the molecular marker linkage map was determined to be approximately 1.0 cM from the RFLP locus R2349. This tight linkage will be useful for marker-aided transfer of the WCG in hybrid rice breeding and for map-based cloning.

Molecularmarker diversity and hybrid sterility in indica-japonica rice crosses

The partial sterility of hybrids between the indica and japonica rice subspecies of Asian cultivated rice is a serious constraint for utilizing inter-subspecific heterosis in hybrid rice breeding. In this study, we have investigated the relationship between molecular-marker polymorphism and indica-japonica hybrid fertility using a diallel set involving 20 rice accessions including 9 indica and 11 japonica varieties. Spikelet fertility of the resulting 190 F1s and their parents was examined in a replicated field trial. Intra-subspecific hybrids showed much higher spikelet fertility than inter-subspecific hybrids except in crosses involving wide-compatibility varieties. The parents were surveyed for DNA polymorphism using 96 RFLP and ten SSR markers, which revealed extensive genetic differentiation between indica and japonica varieties. A large number of markers detected highly significant effects on hybrid fertility. The chromosomal locations for many of the positive markers coincided well with previously identified loci for hybrid sterility. The correlation between hybrid fertility and parental distance was low in both intra- and inter-subspecific crosses. The results suggest that the genetic basis of indica-japonica hybrid sterility is complex. It is the qualitative, rather than the quantitative, difference between the parents that determines the fertility of hybrids.

Genetic and cytological analyses of three lethal ovule mutants in soybean (Glycine max; Leguminosae)

Soybean partially sterile mutants 2, 3, and 4 (PS-2, PS-3, and PS-4), recovered from a gene-tagging experiment, were studied to clarify their inheritance, linkage, allelism, and reproductive biology. The PS-2, PS-3, and PS-4 mutants were maintained as heterozygotes and upon self-pollination segregated l fertile: l partially-sterile. For inheritance and linkage tests, all three PS mutants were crossed to flower color mutant Harosoy-w4 and to chlorophyll-deficient (CD) mutants CD-1 and CD-5, also recovered from the tagging study. For allelism tests, reciprocal crosses were made among the three partially sterile mutants. Linkage results indicated that the gene for partial sterility in the PS-2, PS-3, and PS-4 mutants was not linked either to the w4 locus or to the genes for chlorophyll deficiency. Studies of pollen development, pollen viability, and pollen-tube germination indicated no difference between normal and partially sterile genotypes. Linkage and allelism tests indicated that the gene in the three partially sterile mutants was not transmitted through the female when they were used as a female parent. A study of megagametogenesis indicated that the ovules from partially sterile plants had normal embryo sac development. Ovule abortion was due to failure of fertilization.

Depressed gross mineralization and immobilization of nitrogen and changes in microbial population in soil after heat treatment

Partial sterilization causes a change in N mineralization in soil. An increase in the net rate of N mineralization was reported in soil with chloropicrin applied to it (Rovira 1976), and has been well known in soil fumigated with chloroform to measure the microbial biomass N (Jenkinson and Ladd 1981). The gross rate of N mineralization increased in soil inoculated with fresh soil following fumigation with chloroform (Shen et al. 1984). The increased rate of N mineralization has been attributed to the rapid decomposition of organisms killed by partial sterilization (Jenkinson 1966). On the other hand, Nira et al. (1996) reported that the application of a fumigant in a field depressed the gross rates of N mineralization and immobilization in spite of the increase in the net rate of N mineralization. These results suggested that the increase in the net rate of N mineralization by partial sterilization is presumably due to the change in the ratio of N mineralization to immobilization. However, the residues of a fumigant may depress gross N transformation in the field, because the residues may continue to influence microbial activity long after the original treatment (Jenkinson 1966). Some effects of partial sterilization without residues on gross N mineralization remain to be determined.

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.

Lack of mitochondrial and nuclear-encoded subunits of complex I and alteration of the respiratory chain in Nicotiana sylvestris mitochondrial deletion mutants.

We previously have shown that Nicotiana sylvestris cytoplasmic male sterile (CMS) mutants I and II present large mtDNA deletions and that the NAD7 subunit of complex I (the main dehydrogenase of the mitochondrial respiratory chain) is absent in CMS I. Here, we show that, despite a large difference in size in the mtDNA deletion, CMS I and II display similar alterations. Both have an impaired development from germination to flowering, with partial male sterility that becomes complete under low light. Besides NAD7, two other complex I subunits are missing (NAD9 and the nucleus-encoded, 38-kDa subunit), identified on two-dimensional patterns of mitochondrial proteins. Mitochondria isolated from CMS leaves showed altered respiration. Although their succinate oxidation through complex II was close to that of the wild type, oxidation of glycine, a priority substrate of plant mitochondria, was significantly reduced. The remaining activity was much less sensitive to rotenone, indicating the breakdown of Complex I activity. Oxidation of exogenous NADH (coupled to proton gradient generation and partly sensitive to rotenone) was strongly increased. These results suggest respiratory compensation mechanisms involving additional NADH dehydrogenases to complex I. Finally, the capacity of the cyanide-resistant alternative oxidase pathway was enhanced in CMS, and higher amounts of enzyme were evidenced by immunodetection.

The maizedesynaptic1 mutation disrupts meiotic chromosome synapsis

In most eukaryotes, homologous chromosomes undergo synapsis during the first meiotic prophase. A consequence of mutations that interfere with the fidelity or completeness of synapsis can be failure in the formation or maintenance of bivalents, resulting in univalent formation at diakinesis and production of unbalanced spores or gametes. Such mutations, termed desynaptic mutations, can result in complete or partial sterility. We have examined the effect of the maize desynaptic1-9101 mutation on synapsis, using the nuclear spread technique and electron microscopy to examine microsporocytes ranging from early pachytene until the diplotene stage of prophase I. Throughout the pachytene stage, there was an average of about 10 sites of lateral element divergence (indicating nonhomologous synapsis), and during middle and late pachytene, an average of two and three sites of foldback (intrachromosomal) synapsis, per mutant nucleus, respectively. By the diplotene stage, the number of sites of lateral element divergence had decreased to seven, and there was an average of one foldback synapsis site per nucleus. Lateral element divergence and foldback synapsis were not found in spread pachytene nuclei from normal plants. These results imply that the normal expression of the dsy1 gene is essential for the restriction of chromosome synapsis to homologues. The abundance of nonhomologous synapsis and the persistence of extended stretches of unsynapsed axial elements throughout the pachytene stage of dsy1–9101 meiocytes suggests that this mutation disrupts both the fidelity of homology search and the forward course of the synaptic process. This mutation may identify a maize mismatch repair gene. Dev. Genet. 21:146–159, 1997. © 1997 Wiley-Liss, Inc.

Boron requirement for reproductive development in wheat

The effect of boron (B) deficiency on reproductive development was examined in a wheat line SW41 at 4 B levels in a field experiment. The soil B levels (designated B0, B1, B2, B3) ranged from 0.1 to 0.2 mg hot water soluble B kg1. No effect on vegetative growth was detected at any of the B levels, but the number of grains perear increased with B. from 7 in BO to 21 in B3; and Grain Set Index (GSI) also increased from 22 to 60%. At ear emergence, B content (mg B kg1 DW) of the ear ranged from 2.2 to 3.1. and of the flag leaf from 4.1 to 4.7. but these bore slight to no relationship to the number of grains per ear or GSI. Higher B concentrations were found in the carpel, and higher still in the anthers. More significantly, grain set was closely correlated with B in the carpel (R2 = 0.86) and anthers (R2 = 0.77). The significant correlation between GSI and carpel and anther B was confirmed with a larger set of data. With 7 mg B kg−1 DW in the anthers and 5 mg B kg−1 DW in the carpel, the number of grains per ear was doubled when cross pollination with B deficiency tolerant Fang 60 growing near by was allowed. In ears with 9 mg B kg−1 in the anthers and 8 mg B kg−1 in the carpel the effect of cross pollination was smaller, but still significant. The critical deficiency concentration (CDC) of B for the anthers was determined at 10 mg B kg−1 and for the carpel at 8 mg B kg−1.Histological examination of SW41 anthers revealed that microsporogenesis in B-deficient plants proceeded normally up to at least the uninucleate, vacuolate stage. However, pollen maturation was severely affected resulting in shrivelled pollen grains. The programmed development of the tapetum and endothecial layers appeared normal in anthers where partial or complete sterility occurred.It is concluded that reproductive development in wheat requires more B than vegetative growth. The B requirement of the male reproductive organ, the anthers, was also greater than that of the carpel. Since the B requirement in the carpel for successful fertilization and grain set probably also reflects B requirement for pollen germination, it is suggested that B requirement for female gamete development may be lower than the apparent requirement of the carpel.

Antisense and Sense CHS cDNA Expressed by a Tapetum-specific Promoter Causes Partial Male Sterility in Transgenic Tobacco

Chalcone synthase (CHS) is a key enzyme in the biosynthesis of all classes of flavonoids in plants. An antisense or sense CHS cDNA of tea under the regulation of a tapetum-specific promoter of rice was introduced into tobacco by Agrobacterium-mediated transformation. A reduction in the number of fertile pollen grains was observed in four out of 27 antisense CHS transformants and in five out of 26 sense CHS transformants. The distorted pollen grains of transformants lacked starch and flavonols. Fluorescein diacetate staining indicated abortion started at the late uninucleate microspore stage. The antisense or sense transgene would affect the pollen fertility.

Commercial production of avidin from transgenic maize: characterization of transformant, production, processing, extraction and purification

We have produced in transgenic maize seed the glycoprotein, avidin, which is native to avian, reptilian, and amphibian egg white. A transformant showing high-level expression of avidin was selected. Southern blot data revealed that four copies of the gene are present in this transformant. The foreign protein represents >2% of aqueous soluble extracted protein from populations of dry seed, a level higher than any heterologous protein previously reported for maize. In seed, greater than 55% of the extractable transgenic protein is present in the embryo, an organ representing only 12% of the dry weight of the seed. This indicates that the ubiquitin promoter which is generally considered to be constitutive, in this case may be showing a strong tissue preference in the seed. The mature protein is primarily localized to the intercellular spaces. An interesting trait of the transgenic plants expressing avidin is that the presence of the gene correlates with partial or total male sterility. Seed populations from transgenic plants were maintained by outcrossing and segregate 1:1 for the trait. In generations T2–T4, avidin expression remained high at 2.3% (230 mg/kg seed) of extractable protein from seed, though it varied from 1.5 to 3.0%. However, levels of expression did not appear to depend on pollen parent or growing location. Cracked and flaked kernels stored at −29°C or 10 °C for up to three months showed no significant loss of avidin activity. Commercial processing of harvested seed also generated no apparent loss of activity. The protein was purified to greater than 90% purity by affinity chromatography after extraction from ground mature maize seed. Physical characterization of purified maize-derived avidin demonstrated that the N-terminal amino acid sequence and biotin binding characteristics are identical to the native protein with near identical molecular weight and glycosylation. This study shows that producing avidin from maize is not only possible but has practical advantages over current methods.

Interspecific Oryza Sativa L. X O. Glaberrima Steud. progenies in upland rice improvement

Fertile interspecific progenies between Oryza sativa L. and O. glaberrima Steud. were produced through backcrossing and doubled haploid breeding (DHB). Backcrossing with the O. sativa parents increased fertility and helped combine the O. sativa and O. glaberrima features. The use of DHB to generate a large proportion of doubled haploids from interspecific F2 hybrids, helped overcome constraints associated with the conventional breeding of these species, such as: (1) slow fixation of the lines, (2) frequent partial sterility of the progenies and (3) low recovery of useful recombinants. Although true interspecific progenies between O. sativa and O. glaberrima were generally rare, their occurrence in some populations was as high as 30%. Some progenies combined the high yield potential of O. sativa, a result of high spikelet number caused by secondary branches on the panicle, with useful traits of O. glaberrima such as rapid leaf canopy establishment and high N responsiveness. The progenies partly inherited the O. glaberrima parents' high specific leaf area (SLA) during early growth, theoretically improving competitiveness with weeds, and from the O. sativa parents the rapid decrease in SLA towards the reproductive stage, theoretically allowing for high leaf photosynthetic rates and high grain yield. Research is in progress to develop new interspecific plant type concepts for resource poor, weed prone upland rice environments in West Africa.

Deficiency of cox1 gene expression in wheat plants with Aegilops columnaris cytoplasm.

Wheat plants with Aegilops columnaris cytoplasm are characterized by growth inhibition and partial male sterility and show an impaired mitochondrial cytochrome c oxidase activity. We designed this study to clarify the functional relationship between this impaired cytochrome c oxidase activity and possible structural alterations to the mitochondrial genes cox1, cox2 and cox3 that encode three subunits of the cytochrome c oxidase. Using restriction mapping and DNA sequencing, we found major rearrangements in the flanking regions of the cox1 and cox3 genes. In Northern-blot analysis, we detected two different cox3 transcripts and a reduced level of a cox2 transcript, whereas we could not detect a transcript of cox1. These results suggest that rearrangements of the flanking regions of the cox1 gene may result in the severe suppression of its transcription, and subsequently, may lead to the impaired cytochrome c oxidase activity.

SUBOPTIMAL VIRULENCE OF AN INSECT-PARASITIC NEMATODE.

Recent considerations of parasite virulence have focused on the adverse effects that parasites can have on the survival of their hosts. Many parasites, however, reduce host fitness by an equally deleterious but different means, by causing partial or complete sterility of their hosts. A model of optimal parasite virulence is developed in which a quantity of host resources can be allocated to either host or parasite reproduction. Increases in parasite reproduction thus cause reductions in host fertility. The model shows that under a wide variety of ecological conditions, such parasites should completely sterilize their hosts. Only when opportunities for horizontal transmission are very limited should the parasites appropriate less than all of a host's reproductive resources. Field and laboratory evidence shows that the nematode parasite Howardula aoronymphium is relatively avirulent to one of its principal host species, Drosophila falleni, whereas it is much more virulent to D. putrida and D. neotestacea, suggesting that there may be substantial vertical transmission in D. falleni. However, epidemiological studies in the field and laboratory assays of host specificity strongly suggest that the three host species share a single parasite pool in natural populations, indicating that parasites in all three host species experience high levels of horizontal transmission. Thus, the low virulence of H. aoronymphium to D. falleni is not consistent with the model of optimal parasite virulence. It is proposed that this suboptimal virulence in D. falleni is a consequence of populations of H. aoronymphium being selected to exploit simultaneously several different host species. As a result, virulence may not be optimal in any one host. One must, therefore, consider the full range of host species in assessing a parasite's virulence.

The Broom of the Sorcerer's Apprentice: The Fine Structure of a Chromosomal Region Causing Reproductive Isolation Between Two Sibling Species of Drosophila

How many genes contribute to reproductive isolation between closely related species? We determined the number of genes located in the 9D-12B region of the Drosophila mauritiana X chromosome that cause hybrid male sterility in a D. simulans background. Previous low resolution studies suggested that a single hybrid sterility factor was associated with this region. In this study, by taking advantage of a cluster of visible and DNA markers, we identified three D. mauritiana factors in this region and then subjected one of them to detailed analysis. This factor again turned out to be comprised of three factors; one of which, mapped to within 200 kb, may in fact be two factors. The title refers to this exercise of splitting sterile introgressions into ever smaller ones, each of which retains partial or full sterility effects. In a region representing a mere 3% of the Drosophila genome, no fewer than six loci of hybrid sterility were identified between two sibling species that have not shown clear divergence at the molecular level. These results suggest that levels of genetic divergence between closely related species may be quite high for functionally important traits even when the opposite is true for randomly chosen loci.

Examination of sclerotial germination in Sclerotinia minor with an in vitro model

An in vitro model was developed to examine the effect of surface microflora and exogenous nutrient on sclerotial germination of Sclerotinia minor. Germinated sclerotia were identified by the presence of appressoria on the plastic Petri dish. Surface sterilised field sclerotia germinated at maximum rates on water agar, but unsterilised sclerotia failed to germinate, even after drying and rewetting, indicating that sclerotia of S. minor are unlikely to germinate spontaneously in the presence of soil microflora. Partial surface sterilisation gave intermediate germination rates, which were enhanced two- to four-fold by treatment with sunflower root sap. There was no significant difference in the germination response to root sap from susceptible and resistant sunflower lines, but germination rates were highest with root nutrient obtained from plants during vegetative growth. A positive germination response to peptone and an amino acid mixture implicated amino acids as germination stimuli. Germination of field sclerotia required incubation with root sap for more than 3 days, suggesting that prolonged exposure of sclerotia to root exudates may be required for the onset of stem rot in sunflowers. This is discussed in relation to the dynamics of root growth. Keywords: exogenous nutrient, field sclerotia, germination stimulus.

Partial Male Sterility in Transgenic Tobacco Carrying Antisense and Sense PAL cDNA under the Control of a Tapetum-Specific Promoter

Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) catalyzes the first step in the synthesis of phenylpropanoids. An antisense or sense PAL cDNA of sweet potato under the control of a tapetum-specific promoter of rice was introduced into tobacco. A reduction in pollen fertility was observed in two out of seventeen antisense PAL transformants and in six out of nineteen sense PAL transformants. The pollen fertility of these plants ranged from 8% to 60%. The distorted pollen grains that did not germinate lacked starch and flavonols. PAL activity in anthers at the microspore stage was also reduced to some extent and the level of PAL activity was positively correlated with the number of fertile pollen grains at the flowering stage. Although it was unclear how the antisense or sense transgene affected the PAL activity in anthers, our results clearly demonstrate that the PAL activity in the anther tapetum has a significant effect on the development of microspores.

The mac1 gene: controlling the commitment to the meiotic pathway in maize.

The switch from the vegetative to the reproductive pathway of development in flowering plants requires the commitment of the subepidermal cells of the ovules and anthers to enter the meiotic pathway. These cells, the hypodermal cells, either directly or indirectly form the archesporial cells that, in turn, differentiate into the megasporocytes and microsporocytes. We have isolated a recessive pleiotropic mutation that we have termed multiple archesporial cells1 (mac1) and located it to the short arm of chromosome 10. Its cytological phenotype suggests that this locus plays an important role in the switch of the hypodermal cells from the vegetative to the meiotic (sporogenous) pathway in maize ovules. During normal ovule development in maize, only a single hypodermal cell develops into an archesporial cell and this differentiates into the single megasporocyte. In mac1 mutant ovules several hypodermal cells develop into archesporial cells, and the resulting megasporocytes undergo a normal meiosis. More than one megaspore survives in the tetrad and more than one embryo sac is formed in each ovule. Ears on mutant plants show partial sterility resulting from abnormalities in megaspore differentiation and embryo sac formation. The sporophytic expression of this gene is therefore also important for normal female gametophyte development.

Stress signal, mediated by a Hogl-like MAP kinase, controls sexual development in fission yeast

We identified the phhl + gene that encodes a MAP kinase as the effector of Wis1 MAP kinase kinase in fission yeast, which is highly homologous with HOG1 of S. cerevisiae. Heterothalic phh1 dsiruptant is phenotypically indistinguishable from wis1 deletion mutant, both displaying the same extent of partial sterility and enhanced sensitivity to a variety of stress. In phh1 disruptant, nitrogen starvation-induced expression of ste11 +, a key controller of sexual differentiation, is markedly diminished. Ectopic expression of ste11 + effectively restores fertility, but not stress resistance, to the phh1 disruptant. These data show that stress signal, mediated by a MAP kinase, is required for efficient start of sexual differentiation.

Gender variation, partial male sterility and labile sex expression in gynodioecious Plantago coronopus.

Gynodioecy is 8 breeding system consisting of male, steriles (MS, females) and hermaphrodites (H). There is however within such systems a third, often neglected, class of partially male sterile plants (PMS), i.e. plants with an intermediate sex expression, In natural populations of Plantago coronopus partially male sterile individuals were us common as male steriles (frequencies in the range 1·7-36·8%). These PMS plants constitute a continuous series, linking complete male sterility and hermaphroditism. We discovered that temperature influenced sex expression and the degree of male sterility of PMS individuals, but not of MS and H individuals. Thus, at higher temperatures PMS individuals became more male sterile. Difference in cytoplasmic background of the individuals did nut influence their response to temperature. It is argued that partial male sterility is a normal feature of gynodioecious species and not an abnormality.