Two new loci for hybrid sterility in cultivated rice (Oryza sativa L.)

Female gamete abortion in Indica-Japonica crosses of rice was earlier identified to be due to an allelic interaction at the S-5 locus on chromosome 6. Recently, in other crosses of rice, similar allelic interactions were found at loci designated as S-7 and S-8, located on chromosomes 7 and 6 respectively. All of them are independent of each other. At the S-5 locus, Indica and Japonica rice have S-5 ⁱ and S-5 ^j alleles respectively and Javanicas, such as Ketan Nangka, have a neutral allele S-5 ⁿ .The S-5 ⁱ /S-5 ^j genotype is semi-sterile due to partial abortion of female gametes carrying S-5 ^j , but both the S-5 ⁿ /S-5 ⁱ and S-5 ⁿ /S-5 ^j genotypes are fertile. The S-5 ⁿ allele is thus a wide-compatibility gene (WCG), and parents homozygous for this allele are called wide-compatible varieties (WCV). Such parents when crossed with Indica or Japonica varieties do not show F₁ hybrid sterility. Wide-compatible parents have been used to overcome sterility barriers in crosses between Indica and Japonica rice. However, a Javanica variety, Ketan Nangka (WCV), showed typical hybrid sterility when crossed to the Indian varieties N22 and Jaya. Further, Dular, another WCV from India, showed typical hybrid sterility when crossed to an IRRI line, IR2061-628-1-6-4-3(IR2061-628). By genetic analyses using isozyme markers, a new locus causing hybrid sterility in crosses between Ketan Nangka and the Indicas was located near isozyme loci Est-1 and Mal-1 on chromosome 4, and was designated as S-9. Another new locus for hybrid sterility in the crosses between Dular and the IR2061-628 was identified and was found linked to four isozyme loci, Sdh-1, Pox-2, Acp-1 and Acp-2, on chromosome 12. It was designated as S-15. On the basis of allelic interactions causing female-gamete abortion, two alleles were found at S-9, S-9 ^kn in Ketan Nangka and S-9 ⁱ in N22 and Jaya. In the heterozygote, S-9 ^kn /S-9 ⁱ , which was semisterile, female gametes carrying S-9 ^kn were aborted. The hybrid of Dular and IR2061-628, with a genetic constitution of S-15 ^Du /S-15 ⁱ , was semi-sterile and the female gametes carrying S-15 ^Du were aborted. A Japonica tester variety, Akihikari, and an Indica variety, IR36, were found to have neutral alleles, S-9 nand S-15 n, at these loci, in addition to S-7 nand at S-7. The accumulation of three neutral alleles into a breeding line should help solve the hybrid sterility problem in wide crosses of rice.     

Improved mating efficiency inAcetabularia acetabulum: recovery of 48–100% of the expected zygotes

Summary We have improved zygote recovery 11–1,000 fold by optimizing the physiology of gamete release and mating inAcetabularia acetabulum. Gamete release was affected by agar purity, concentration, and volume/gametangial pair. Cold pre-treatment of gametangia (14–30 d at 10°C in the dark) synchronized subsequent gamete release at 21°C in the light. Cold pre-treatment was nearly twice as effective in synchronizing subsequent gamete release when intact, gametangia-bearing caps rather than isolated gametangia were pretreated. Synchronizing gamete release doubled mating efficiency. In a wild-type laboratory strain ofA. acetabulum, there were 1,561±207 gametes/gametangium which had half-lives of 14.5 d in 0.1% seawater-agar. We recovered 48–93% of the expected numbers of zygotes from a mass mating of 8 to 1,226 gametangia and 11–128% of the expected numbers of zygotes from mating single gametangial pairs: the large range in the calculated mating efficiency may be attributable to the variation in the numbers of gametes made per gametangium. Zygote recovery from single gametangial pairs was highly dependent on the volume of mating matrix. In addition, most zygotes recovered were unattached to any other zygotes in the subsequent generation (> 95% single cells from matings of 1–500 gametangial pairs). Our improvements in mating conditions and zygote recovery (1) have facilitated cell manipulation and culture ofA. acetabulum in the laboratory; and (2) have made controlled crosses for selection and genetic analysis of mutants feasible. These advances have removed a major barrier to genetic analysis of development inAcetabularia.Abbreviations LB Luria-Bertani bacteriological broth - SE standard error of the mean - T_g agar gelling temperatures - DAPI 4,6-diamidino-2-phenylindole     

OVULE PACKAGING IN STOCHASTIC POLLINATION AND FERTILIZATION ENVIRONMENTS

The modular morphology of plants has important consequences for reproductive strategies. Ovules are packaged in discrete structures (flowers) that usually vary stochastically in pollen capture and ovule fertilization, because of the vagaries of pollen transfer by external agents. Different ovule packaging schemes may use limited reproductive resources more or less effectively, so that some number of ovules per flower may be optimal, given the prevailing probabilities of ovule fertilization. I derive a phenotypic model for ovule number per flower that maximizes the expected total ovule fertilizations on a plant when pollination and fertilization vary randomly among individual flowers. This model predicts that, except for small or inexpensive flowers, ovules should be “oversupplied” relative to the mean receipt of pollen tubes, so that pollen limitation of seed set should be common. Published data are congruent with this prediction. Additional hypotheses on the relation of ovule packaging to floral cost, plant size, and variance in pollen receipt are suggested by the model, but few data exist to evaluate these hypotheses.     

Peculiarities in PMC Meiosis of Pisum sativum

Summary Nemesia strumosa plants were discovered which had styles capable of discriminating among incompatible pollen tubes from different pollinators, allowing growth of some but not others. All but 3 of 26 families tested had at least some members with discriminating styles (DS). Presence and level of DS was independent of S genotype. Plants with pseudo-self-compatiblity (PSC) levels greater than 10% had the trait, though many plants with strong DS had PSC levels less than 10%. Self pollination of highly DS plants produced mostly DS offspring, but of differing sensitivities. Some progenies from crosses between a family of highly DS plants and unrelated, probably low DS plants segregated half DS and half non-DS, while others consisted of mostly DS or mostly non-DS. The DS phenomenon is probably caused by PSC genes.Scientific Journal Series Paper No. 11,677 of the Minnesota Agricultural Experiment Station     

Role of evolutionary and ecological factors in the reproductive success and the spatial genetic structure of the temperate gorgonian Paramuricea clavata

Dispersal and mating features strongly influence the evolutionary dynamics and the spatial genetic structure (SGS) of marine populations. For the first time in a marine invertebrate, we examined individual reproductive success, by conducting larval paternity assignments after a natural spawning event, combined with a small‐scale SGS analysis within a population of the gorgonian Paramuricea clavata. Thirty four percent of the larvae were sired by male colonies surrounding the brooding female colonies, revealing that the bulk of the mating was accomplished by males from outside the studied area. Male success increased with male height and decreased with increasing male to female distance. The parentage analyses, with a strong level of self‐recruitment (25%), unveiled the occurrence of a complex family structure at a small spatial scale, consistent with the limited larval dispersal of this species. However, no evidence of small scale SGS was revealed despite this family structure. Furthermore, temporal genetic structure was not observed, which appears to be related to the rather large effective population size. The low level of inbreeding found suggests a pattern of random mating in this species, which disagrees with expectations that limited larval dispersal should lead to biparental inbreeding. Surface brooding and investment in sexual reproduction in P. clavata contribute to multiple paternity (on average 6.4 fathers were assigned per brood), which enhance genetic diversity of the brood. Several factors may have contributed to the lack of biparental inbreeding in our study such as (i) the lack of sperm limitation at a small scale, (ii) multiple paternity, and (iii) the large effective population size. Thus, our results indicate that limited larval dispersal and complex family structure do not necessarily lead to biparental inbreeding and SGS. In the framework of conservation purposes, our results suggested that colony size, proximity among colonies and the population size should be taken into consideration for restoration projects.     

Identification and characterization of segregation distortion loci along chromosome 5B in tetraploid wheat

Segregation distortion genes are widespread in plants and animals and function by their effect on competition among gametes for preferential fertilization. In this study, we evaluated the segregation distortion of molecular markers in multiple reciprocal backcross populations derived from unique cytogenetic stocks involving the durum cultivar Langdon (LDN) and wild emmer accessions that allowed us to study the effects of chromosome 5B in isolation. No segregation distortion of female gametes was observed, but three populations developed to analyze segregation of male gametes had genomic regions containing markers with skewed segregation ratios. One region of distortion was due to preferential transmission of LDN alleles over wild emmer alleles through male gametes. Another region required the presence of LDN 5B chromosomes in the female for preferential fertilization by male gametes harboring LDN alleles indicating that the corresponding genes in the female gametes can govern genes affecting segregation distortion of male gametes. A third region of distortion was the result of preferential transmission of wild emmer alleles over LDN alleles through male gametes. These results indicate the existence of different distorter/meiotic drive elements among different genotypes and show that distortion factors along wheat chromosome 5B differ in chromosomal location as well as underlying mechanisms.     

Co‐evolution of gametes of the Greater Bandicoot Rat,Bandicota indica – a murine rodent from South‐East Asia

Most Old World mice and rats, subfamily Murinae, have a spermatozoon with an apical hook, a long tail and, as seen typically in eutherian mammals, a bilaterally flattened head. Dramatically different from this are the sperm of the Greater Bandicoot Rat, Bandicota indica. Here, we ask the question has the structure of the sperm head co‐evolved with that of the egg coat, the zona pellucida? For this, we first summarise the morphological features of the spermatozoon of B. indica that may relate to zona pellucida penetration at the time of fertilisation, and we confirm that the sperm head is generally round, not bilaterally flattened, in profile and has a huge acrosome. We then show that the zona pellucida around oocytes in tertiary follicles also differs from that of the other murine rodents in being only about 4 μm thick and, as demonstrated by lectin staining, has an unusual abundance of alpha‐L‐fucose. These findings indicate that both the male and female gametes of this South‐East Asian murine rodent are highly divergent in their structural organisation. One of the functional implications of this probably relates to sperm–zona interactions and the release of acrosomal enzymes that probably facilitate penetration by digestion of the zona matrix at the time of fertilisation.     

In vitro fertilization as a tool for investigating sexual reproduction of angiosperms

In vitro fertilization (IVF) of isolated male and female gametes of flowering plants was first accomplished in the last decade. Successful isolation of male and female gametes, and culturing of in vitro zygotes to form new plants, is a prelude to the use of IVF for research into the cellular and molecular control of fertilization in higher plants and its application as a tool in biotechnology. Genes unique to male and female gametes and zygotes of higher plants, although currently incompletely characterized, are expected to permit direct molecular dissection of fertilization. By applying IVF and microculture to zygotes and endosperm obtained by both in vivo and in vitro methods, newly activated fusion products may be observed and manipulated in media where they are directly accessible to the techniques of molecular cell biology. IVF and zygote culture may also offer potential for creating new hybrid plants by fusing isolated gametes from different species to produce unique zygotes and ultimately plants that would be impossible to obtain using typical crossing techniques. Transformation and regeneration frequencies using IVF may also be high enough to avoid the necessity of adding controversial antibiotic and herbicide resistant genes to screen transformed products. This review describes advances using IVF in plant sexual reproduction and discusses its potential in the genetic improvement of flowering plants.     

Inbreeding depression of sperm traits in the zebra finch Taeniopygia guttata

Inbreeding depression, or the reduction in fitness due to mating between close relatives, is a key issue in biology today. Inbreeding negatively affects many fitness‐related traits, including survival and reproductive success. Despite this, very few studies have quantified the effects of inbreeding on vertebrate gamete traits under controlled breeding conditions using a full‐sib mating approach. Here, we provide comprehensive evidence for the negative effect of inbreeding on sperm traits in a bird, the zebra finch Taeniopygia guttata. We compared sperm characteristics of both inbred (pedigree F = 0.25) and outbred (pedigree F = 0) individuals from two captive populations, one domesticated and one recently wild‐derived, raised under standardized conditions. As normal spermatozoa morphology did not differ consistently between inbred and outbred individuals, our study confirms the hypothesis that sperm morphology is not particularly susceptible to inbreeding depression. Inbreeding did, however, lead to significantly lower sperm motility and a substantially higher percentage of abnormal spermatozoa in ejaculate. These results were consistent across both study populations, confirming the generality and reliability of our findings.     

Ubiquitin-proteasome pathway modulates mouse oocyte meiotic maturation and fertilization via regulation of MAPK cascade and cyclin B1 degradation

Degradation of proteins mediated by ubiquitin-proteasome pathway (UPP) plays important roles in the regulation of eukaryotic cell cycle. In this study, the functional roles and regulatory mechanisms of UPP in mouse oocyte meiotic maturation, fertilization, and early embryonic cleavage were studied by drug-treatment, Western blot, antibody microinjection, and confocal microscopy. The meiotic resumption of both cumulus-enclosed oocytes and denuded oocytes was stimulated by two potent, reversible, and cell-permeable proteasome inhibitors, ALLN and MG-132. The metaphase I spindle assembly was prevented, and the distribution of ubiquitin, cyclin B1, and polo-like kinase 1 (Plk1) was also distorted. When UPP was inhibited, mitogen-activated protein kinase (MAPK)/p90rsk phosphorylation was not affected, but the cyclin B1 degradation that occurs during normal metaphase-anaphase transition was not observed. During oocyte activation, the emission of second polar body (PB2) and the pronuclear formation were inhibited by ALLN or MG-132. In oocytes microinjected with ubiquitin antibodies, PB2 emission and pronuclear formation were also inhibited after in vitro fertilization. The expression of cyclin B1 and the phosphorylation of MAPK/p90rsk could still be detected in ALLN or MG-132-treated oocytes even at 8 h after parthenogenetic activation or insemination, which may account for the inhibition of PB2 emission and pronuclear formation. We also for the first time investigated the subcellular localization of ubiquitin protein at different stages of oocyte and early embryo development. Ubiquitin protein was accumulated in the germinal vesicle (GV), the region between the separating homologous chromosomes, the midbody, the pronuclei, and the region between the separating sister chromatids. In conclusion, our results suggest that the UPP plays important roles in oocyte meiosis resumption, spindle assembly, polar body emission, and pronuclear formation, probably by regulating cyclin B1 degradation and MAPK/p90rsk phosphorylation.