Towards an understanding of the genetics of human male infertility: lessons from flies

It has been argued that about 4–5% of male adults suffer from infertility due to a genetic causation. From studies in the fruitfly Drosophila, there is evidence that up to 1500 recessive genes contribute to male fertility in that species. Here we suggest that the control of human male fertility is of at least comparable genetic complexity. However, because of small family size, conventional positional cloning methods for identifying human genes will have little impact on the dissection of male infertility. A critical selection of well-defined infertility phenotypes in model organisms, combined with identification of the genes involved and their orthologues in man, might reveal the genes that contribute to human male infertility.     

Ecological and genetic factors contributing to the low frequency of male sterility in Chamaecrista Fasciculata (Fabaceae)

Bumble bee pollinated Chamaecrista fasciculata provides pollen as the sole reward to its pollinators. Male sterility, expressed as an absence or nearly complete absence of pollen production, occurs in low frequency in populations of C. fasciculata. Here we describe experiments, using C. fasciculata, to examine frequently cited determinants of the spread and maintenance of male sterility: compensation and the genetic basis of male sterility. In addition, we examine the role the pollination system plays in determining the reproductive success of the male steriles. Seventeen populations in Maryland, Illinois, and Kansas were surveyed and found to range from 0 to 6% male sterility per population. An artificial population of male-sterile simulants and hermaphrodites was created to examine how the local frequency of nonrewarding male steriles might affect male-sterile female reproductive success. Male steriles performed equally poorly, with respect to seed production, whether surrounded by other male-sterile simulants or hermaphrodites. Compensation was examined by comparison of male steriles and hermaphrodites with respect to several reproductive and nonreproductive characters. Male steriles outperformed hermaphrodites in terms of nonreproductive biomass, but performed equally in terms of ovule number and produced many fewer flowers. The genetic basis of male sterility was examined by performing both intra- and interpopulational crosses of male steriles to hermaphrodites and indicate that male sterility is not purely cytoplasmic. The low frequency of male sterility in C. fasciculata populations may reflect reduced female reproductive success because of pollinator avoidance, lack of reproductive compensation, and a mode of inheritance that is not purely cytoplasmic.     

A Moricandia arvensis– based cytoplasmic male sterility and fertility restoration system in Brassica juncea

 A cytoplasmic male-sterility system has been developed in mustard (Brassica juncea) following repeated backcrossings of the somatic hybrid Moricandia arvensis (2n=28, MM)+B. juncea (2n=36, AABB), carrying mitochondria and chloroplasts from M. arvensis, to Brassica juncea. Cytoplasmic male-sterile (CMS) plants are similar to normal B. juncea; however, the leaves exhibit severe chlorosis resulting in delayed flowering. Flowers are normal with slender, non-dehiscent anthers and excellent nectaries. CMS plants show regular meiosis with pollen degeneration occurring during microsporogenesis. Female fertility was normal. Genetic information for fertility restoration was introgressed following the development of a M. arvensis monosomic addition line on CMS B. juncea. The additional chromosome paired allosyndetically with one of the B. juncea bivalents and allowed introgression. The putative restorer plant also exhibited severe chlorosis similar to CMS plants but possessed 89% and 73% pollen and seed fertility, respectively, which subsequently increased to 96% and 87% in the selfed progeny. The progeny of the cross of CMS line with the restorer line MJR-15, segregated into 1 fertile : 1 sterile. The CMS (Moricandia) B. juncea, the restorer (MJR-15), and fertility restored F₁ plants possess similar cytoplasmic organellar genomes as revealed by ‘Southern’ analysis. Received: 17 September 1997 / Accepted: 18 February 1998     

Quantitative ovule sterility in Medicago sativa

 Ovule sterility was found to be associated with callose deposition in B17, a plant with low fertility from the alfalfa cv Blazer XL. The site of callose deposition, which began during embryo-sac development and affected 81% of the ovules in mature florets, at random positions in the ovary, appeared to be the embryo-sac wall or the integumentary tapetum. The fertile ovules of B17 transmitted the ovule-sterility trait to the progenies, thereby demonstrating a sporophytic genetic control. B17 was crossed with P13, a Peruvian plant with 5% callosized ovules, to generate reciprocal F₁ populations, and an F₁ plant (91% callosized ovules) was used to obtain the backcross populations. B17 was also crossed to unrelated, highly fertile, plants. S₁ progenies from B17 and P13 were also studied. All the progeny populations displayed continuous variation for the percentage of sterile ovules, supporting a polygenic control. Narrow-sense heritability estimated by offspring-midparent regression was 0.85. Reduced transmission of the sterility trait through the pollen is hypothesized to explain the difference between reciprocal crosses. Six progeny plants showing 100% callosized ovules proved to be female-sterile. Ovule sterility could be an important component of the generally observed low realized seed potential in alfalfa. Received: 2 March 1998 / Accepted: 28 May 1998     

Nuclear-cytoplasmic interactions in restoration of male fertility in the ‘9E’ and A4 CMS-inducing cytoplasms of sorghum

 The genetics of male-fertility restoration in sorghum in the “9E” and A4 CMS-inducing cytoplasms, was studied by crossing a number of fertility restorer lines of A1 cytoplasm to CMS lines [9E]T×398 and [A4]T×398 and the line [9E]Milo-10, which was obtained by backcrossing Milo-10 to [9E]T×398. It was revealed that both A4 and “9E” cytoplasms are characterized by a sporophytic mode of restoration of male fertility. Depending on the nuclear background of the male parents, fertility restoration was controlled by one or two dominant genes. Fertility-restorer genes of one of the tester lines, KVV-114, were effective in [9E]T×398 but could not restore [9E]Milo-10. A fertile line obtained from the fertile hybrid [9E]T×398/KVV-112, with “9E” cytoplasm, also failed to restore [9E]Milo-10. In a number of hybrid combinations with both A4 and “9E” cytoplasms a novel and unusual phenomenon of gradual restoration of male fertility in subsequent backcross generations was observed. Pollen from the fertile revertants did not transmit fertility restoration in progeny from crosses with the original CMS line and was poorly transmitted in sib-crosses. The appearance of fertile revertants and the different reactions of different CMS lines with the same cytoplasm in test-crosses may be caused by the action of recessive nuclear genes of the recurrent male parents that were accumulated during backcrossing; these may induce changes in cytoplasmic genes controlling CMS. Received: 5 March 1998 / Accepted: 7 April 1998     

The high level of wide-compatibility of variety ‘Dular’ has a complex genetic basis

Wide-compatibility varieties (WCVs) are a special class of rice germplasm that is able to produce fertile hybrids when crossed to both indica and japonica rice varieties. WCVs may differ greatly in their spectrum and level of compatibility. The objective of this study was to determine the genetic basis of wide-compatibility conferred by ‘Dular’, a landrace variety from India that has demonstrated a high level of wide-compatibility in previous studies with a broad range of indica and japonica varieties. A three-way cross (‘Balilla/Dular//Nanjing 11’) was made and the resulting F₁ population evaluated in the field for spikelet fertility. A total of 235 plants from this population was assayed individually for restriction fragment length polymorphisms (RFLPs) at 159 marker loci covering the entire rice genome at regular intervals. Quantitative trait locus (QTL) analysis identified 5 loci, located on chromosomes 1, 3, 5, 6 and 8, as having significant effects on hybrid fertility, which jointly explained 55.5% of the fertility variation in this population. The QTL on chromosome 5 ( f5) showed the largest effect on hybrid fertility, followed by those on chromosomes 6 ( f6), 3 ( f3) and 1 ( f1), with the one on chromosome 8 ( f8) having the smallest effect. Genotypes each composed of an allele from ‘Dular’ and an allele from ‘Nanjing 11’ at four ( f3, f5, f6 and f8) of the five QTLs contributed to the increase of fertility in the population. In contrast, the genotype composed of alleles from ‘Balilla’ and ‘Nanjing 11’ at the fifth locus ( f1) was in the direction of increasing fertility. Analysis of variance using marker genotypes at the five QTLs as the groups detected two interactions involving four of the five loci, a 2-locus interaction between f5 and f8 and a 3-locus interaction among f3, f5 and f6. The level of hybrid fertility is the result of complex interactions among these loci. The implication of the present findings in the utilization of the wide-compatibility of ‘Dular’ in rice breeding programs is also discussed. Received: 21 October 1997 / Accepted: 30 December 1997     

水稻细胞质雄性不育系与保持系的呼吸途径比较

比较水稻细胞质雄性不育系珍汕97A及其保持系珍汕97B之幼穗、叶片和花药的呼吸代谢。结果表明：不育系花药的总呼吸速率、抗氰呼吸所占总呼吸比例和细胞色素氧化酶（COD）、苹果酸脱氢酶（MDH）和6－磷酸葡萄糖脱氢酶（6－PGDH）活性低于保持系;幼穗中则仅6－PGDH低于保持系;叶片间各指标均无差异。Na3PO4可抑制保持系的叶片和幼穗及不育系叶片总呼吸的30％,而仅能抑制不育系幼穗总呼吸的24％;丙二酸则抑制不育系与保持系的叶片和幼穗的总呼吸的70％。     

HSP_(70)基因表达对高粱育性的影响(英文)

高粱细胞质雄性不育系３１９７Ａ（３Ａ）在常温条件下是不育的（Ｆｉｇｓ．１１＆２）,经热激（４５℃）诱导不同程度地恢复了育性（Ｆｉｇｓ．１３＆４）,为研究其不育机理提供了线索。热激２ｈ后,３Ａ中即可产生一类线粒体热激蛋白（ＨＳＰｓ）。其中,分子量为７０ｋＤ的ＨＳＰ７０含量最高,也最为稳定。不过,３Ａ中ＨＳＰｓ的稳定性弱于保持系３１９７Ｂ（３Ｂ）（Ｆｉｇ．２,Ｐａｎｅｌｓ１～４）。放线菌素Ｄ抑制ＨＳＰｓ的合成,而氯霉素无此作用（Ｆｉｇ．２,Ｐａｎｅｌｓ５＆６）,表明：ＨＳＰｓ是由核基因编码、在细胞质中合成、再跨膜转运到线粒体中的。３Ａ幼穗经热激后,线粒体的总蛋白量猛增了２．７倍（Ｆｉｇ．３）,达到３Ｂ的水平,育性亦变为可育的。Ｆｉｇ．４表明：ＨＳＰ７０反义链ｃＤＮＡ（Ｒ１）能进入到３Ｂ花药细胞中,并与靶ＲＮＡ（ＨＳＣ７０ｍＲＮＡ）结合,而对照、正义链ｃＤＮＡ（Ｄ）链无此反应。由此、再增加一个通用保守序列的反义链ｃＤＮＡ（Ｒ２）、共两个探针（Ｒ１、Ｒ２）,可以检测到：３Ａ在常温下没有能力合成ＨＳＣ７０ｍＲＮＡ（Ｆｉｇ．５）,而在热激条件下,转变为有能力（Ｆｉｇ．６）。启示：３Ａ在热激条件下由不育转变为可育     

雄性核不育水稻育性转换的光周期效应指数值(PE)和温度效应指数值(TE)的遗传性初步研究

对比考察了农垦５８ｓ与７００１ｓ、８９０２ｓ与培矮６４ｓ及８９０２ｓ与安农Ｓ１等３个光（温）敏核不育水稻杂交组合的双亲、Ｆ１、Ｂ１、Ｂ２和Ｆ２世代的样本及每一个体的ＰＥ和ＴＥ的变异。无论双亲核不育基因的等位程度及栽培环境的光、温周期如何,在多数情况下都显示了如下的规律：（１）后代样本ＰＥ、ＴＥ的大小虽然形形色色,但都取决于其双亲。Ｆ１表示完全显性甚至超显性。（２）Ｆ２个体的ＰＥ或ＴＥ、尤其同一个体ＰＥ与ＴＥ的集成类型发生有规律的分离和超亲分离,产生形形色色的育性转换类型。在纯粹由雄性不育个体组成的Ｆ２不育分样本中也发生同样分离。（３）ＰＥ或ＴＥ的广义遗传力的估值都大于５０％。据此推断ＰＥ、ＴＥ是两个可遗传并可供选择的独立性状;并对育性转换现象的遗传机制也进行了讨论。