Primary trisomics of rice: origin, morphology, cytology and use in linkage mapping

Twelve primary trisomics of Oryza sativa L. were isolated from the progenies of spontaneous triploids and were transferred by backcrossing to the genetic background of IR36, a widely grown high yielding rice variety. Eleven trisomics can be identified morphologically from one another and from diploids. However, triplo 11 is difficult to distinguish from diploid sibs.—The extra chromosome of each trisomic was identified cytologically at pachytene stage of meiosis, and the chromosomes were numbered according to their length at this stage. The major distinguishing features of each pachytene chromosome were redescribed.—The female transmission rates varied from 15.5% for triplo 1, the longest chromosome, to 43.9% for triplo 12, the shortest chromosome. Seven of the 12 primary trisomics transmitted the extra chromosome through the male. The low level of chromosomal imbalance tolerated by rice and other evidence are interpreted to indicate that this species is a basic diploid.—Genetic segregation for 22 marker genes in the trisomic progenies was studied. Of a possible 264 combinations, involving 22 genes and 12 trisomics, 120 were examined. Marker genes for each of the 12 chromosomes were identified. The results helped establish associations between linkage groups and cytologically identifiable chromosomes of rice for the first time. Relationships between various systems of numbering chromosomes, trisomics, linkage groups and marker genes are described, and a revised linkage map of rice is presented.     

四倍体水稻花药培养筛选初级三体的研究

以同源四倍体水稻 ( Oryza sativa L.)各世代杂种和四倍体籼、粳原种为材料进行花药培养 ,诱导花粉植株再生。根据三体植株表型上相互区别的特性 ,且又显著区别于二倍体 ,对其中所诱导的 1 5个花药培养品系 4 390株 H1花粉植株进行了重点固定和染色体镜检。结果表明 ,花粉 H1植株染色体组成包括二倍体、四倍体和非整倍体 ,其频率分别为 88.0 %、5 .5 3%和 6.67%。鉴定出 2 72株三体 ,占全部花粉植株的 6.2 0 %。对照已配套三体系的形态 ,将鉴定的三体株划分为 9种类型 ,并对其中的 91 2 4 - 7窄叶三体进行粗线期核型分析 ,鉴定为三体 8。将三体 8的种子播种 ,在 H2 代苗期统计额外染色体的传递率 ,三体株占 34 .1 1 % ,其农艺性状也同于 H1亲代     

Selection of Primary Trisomics from Anther Culture of Autotetraploid Rice (Oryza sativa L.)

The hybrids from different generations of autotetraploid rice (Oryza sativa L. ) and the original autotetraploid rice (indica and japonica) were used for anther culture, and the pollen-plantlets from them were induced. Due to the significant difference on phenotype among the trisomics and between trisomics and diploid, 15 lines of 4390 H1 induced plants were selected for chromosome study. Their PMC meiosis were observed. The results showed that the chromosomes from these plants consisted of 2n, 4n and aneuploids, and their ratios were 88.00%, 5.53% and 6.47% respectively. 272 trisomics from 284 aneuploids were identified, which acounted for 6.20% of all the pollen-plants. According to the special characters from the whole set of trisomics, they were classified as 9 types. The 9124- 7 trisomics were designated as triplo-8 by the pachytene analysis. Sowing the seeds of triplo8, the transmission rate of extra chromosome was calculated at the seedling stage of H2. The rate of trisomic was 34.11% of all plants, the agronomic characters were similar to the H1 parent plants.     

Chiasma frequency and position in male and female mice of chromosomes involved in homozygous and heterozygous translocations and tertiary trisomy

Chiasma frequency and position were analyzed at a predominantly late diplotene-diakinesis stage of the first meiotic division in oocytes and spermatocytes from T(1;13)70H homozygotes and heterozygotes, T(2;8)26H heterozygotes and from Ts(I¹³)70H tertiary trisomics of the mouse, Mus musculus. For T70H/T70H, the 13¹ long marker bivalent was studied and for the other karyotypes, analysis was confined to the multivalent configurations adopted by the rearranged chromosomes and their homologues. For the 13¹ bivalent, the chiasma frequency tended to be increased in the female. For the T26H and the T70H multivalents, the chiasma frequencies were higher in the female, largely due to the much higher values in the short interstitial segments. This observed enhancement has been attributed to pairing differences rather than to differences in chiasma forming capability. Both in the telomeric region of the 13¹ bivalent and in the short translocated segments of the reciprocal translocation and tertiary trisomic multivalents, females showed fewer chiasmata than males. The determinations of chiasma position in the 13¹ bivalent indicated chiasma interference with respect to position, leading to clustering of chiasmata somewhat beyond the centromere and towards the telomere of this chromosome.     

Genetic and cytogenetic analyses of the A genome of Triticum monococcum. IX. Cytological behaviour, phenotypic characteristics, breeding behaviour, and fertility of primary, double, and triple trisomics.

Cytogenetic studies in Triticum monococcum (2n = 2x = 14, AA) were initiated by generating a series of primary as well as double and triple trisomics from autotriploids derived from crosses between induced autotetraploids and a diploid progenitor. Analysis of meiotic chromosome behaviour revealed that, with the exception of primary trisomics for chromosome 7A, the chromosome present in triple dose in all other trisomics formed either a bivalent plus a univalent or a trivalent (always V shaped) at diakinesis - metaphase I in approximately equal proportions. Trisomics for chromosome 7A formed a bivalent plus a univalent or a trivalent in approximately a 1:2 ratio. About 99% of the anaphase I segregations in all the trisomics were seven to one pole and eight to the other, suggesting that primary trisomics in T. monococcum form n and n + 1 meiotic products in equal proportions. The double trisomics and triple trisomics formed 5 II + 2 III and 4 II + 3 III during metaphase I, respectively. A majority of the secondary meiocytes from the double and triple trisomics possessed unbalanced chromosome numbers. All the trisomics differed phenotypically from their diploid progenitors. Single primary trisomics for chromosomes 3A and 7A produced distinct morphological features on the basis of which they could be distinguished. The phenotypes of the double and triple trisomics deviated to a greater extent from that of diploids than those of the single trisomics. Less than 50% of the progeny of all primary trisomics were trisomics themselves. Trisomic progeny were not produced in diploid female x trisomic male crosses, indicating that functional n + 1 male gametes were not generated. Diploid as well as trisomic progeny were produced in the reciprocal crosses and upon self-fertilization of the trisomics. The average frequency of trisomic progeny was 9.9%. The fertility of primary trisomics ranged from 3.8% in trisomics for chromosome 1A to 40.6% in trisomics for chromosome 2A and was significantly less than that of diploids (99.6%). The breeding behaviour and low fertility of these trisomics make their maintenance and use in cytogenetic analyses difficult.     

Comparison of the transmission of three trisomies by males and females in the newt Pleurodeles waltlii (author's transl)]

In the newt Pleurodelles waltlii, males and females trisomic for chromosomes 8, 10 and 11 are fertile. Crosses between such trisomics and diploids were carried out. Progeny analysis showed that an extra chromosome is transmitted to half of the gametes of both males and females trisomics. The extra chromosome apparently causes interference in the regular mechanics of meiotic division, so that trisomics throw nonparental aneuploids and polyploids in their progenies. Moreover, some descendants develop chromosome anomalies during embryonic life ; thus, the progeny of trisomics include diploids, parentaltype trisomics, and embryos with new chromosome anomalies. Morphology and chromosome anomalies of the embryos are compared. A possible explanation for the secondarily acquired anomalies are discussed.     

Aneuhaploids and tetrasomics in rice (Oryza sativa L.) derived from anther culture of trisomics.

Eight types of aneuhaploids (Aneuhaplo 4, 5, 6, 8, 9, 10, 11, and 12) and eight types of tetrasomics (Tetraplo 4, 5, 6, 7, 8, 9, 10, and 12) of rice have been obtained from anther culture of trisomics. This paper reports the plant morphology of these aneuploids and their chromosome behavior at metaphase I. Aneuhaploids for different chromosomes are distinguishable from each other and are morphologically similar to the parental trisomics, suggesting that the extra chromosome has similar genetic effects on plant morphology at the haploid level as at the diploid level. Similarly, tetrasomics with different extra chromosomes are distinguishable from each other and are similar morphologically to the parental trisomic. However, stronger changes in morphological characters were observed in tetrasomics compared with trisomics having the same extra chromosome, as a result of a dosage effect of the extra chromosomes. Comparing plant size between aneuhaploid, tetrasomic, and trisomic with the same extra chromosome, it was shown that the trisomic was the largest, the tetrasomic was of medium size, and the aneuhaploid was the smallest, except for those plants with an extra chromosome 8 in which plant size is dramatically decreased in both the aneuhaploid and the tetrasomic. At metaphase I, aneuhaploids showed chromosome configurations of 1 II + 11 I and 13 I. The frequency of the 1 II + 11 I configuration is higher than 70%, indicating that homologous chromosomes in aneuhaploids tend to stay associated in meiosis. Intragenome chromosome pairing (2 II + 9 I), so called secondary association, was observed in the aneuhaploid for chromosome 5. Tetrasomic plants showed 5 kinds of chromosome configurations: 1 IV + 11 II, 1 III + 11 II + 1 I, 13 II, 12 II + 2 I, and 11 II + 4 I. A chromosome configuration of 13 II was often observed in tetrasomics with shorter extra chromosomes and a chromosome configuration of 1 IV + 11 II was often observed in tetrasomics with longer extra chromosomes. Aneuhaploids had complete seed sterility. Tetrasomics showed very poor pollen fertility and complete seed sterility, except for a few shriveled seeds that were observed in Tetraplo 6 and 9. This is the first report in rice where many aneuhaploids and tetrasomics have been characterized. This information will help to further unravel rice aneuploidy and cytogenetics. The aneuploids obtained here will be very useful tools for the study of genetics and breeding in rice.     

Meiosis and the Neo- XY system of Dichroplus vittatus (Melanoplinae, Acrididae): a comparison between sexes

The origin of neo-XY sex systems in Acrididae is usually explained through an X-autosome centric fusion, and the behaviour of the neo-sex chromosomes has been solely studied in males. In this paper we analysed male and female Dichroplus vittatus. The karyotype comprises 2n = 20 chromosomes including 9 pairs of autosomes and a sex chromosome pair that includes a large metacentric neo-X and a small telocentric neo-Y. We compared the meiotic behaviour of the sex bivalent between both sexes. Mean cell autosomal chiasma frequency was low in both sexes and slightly but significantly higher in males than in females. Chiasma frequency of females increased significantly when the sex-bivalent was included. Chiasma distribution was basically distal in both sexes. Behaviour of the neo-XY pair is complex as a priori suggested by its structure, which was analysed in mitosis and meiosis of diploid and polyploid cells. During meiosis, orientation of the neo-XY is highly irregular; only 21% of the metaphase I spermatocytes show standard orientation. In the rest of cells, the alternate or simultaneous activity of an extra kinetochore in the distal end of the short arm (XL) of the neo-X, determined unusual MI orientations and a high frequency of non-disjunction and lagging of the sex-chromosomes. In females, the neo-XX bivalent had a more regular behaviour but showed 17% asynapsis in the XL arm which, in those cases orientated its distal ends towards opposite spindle poles suggesting, again, the activity of a second kinetochore. The dicentric nature and the unstable meiotic behaviour of the sex neo-chromosomes of D. vittatus suggest a recent origin of the sex determination mechanism, with presumable adaptive advantages which could compensate their potential negative heterosis. Our observations suggest that the origin of the neo-sex system was a tandem fusion of two original telocentric X-chromosomes followed by another tandem fusion with the small megameric bivalent and a further pericentric inversion of the neo-X. The remaining autosomal homolog resulted in the neo-Y chromosome. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aneuploidy in guava

Aneuploids have been identified cytomorphologically in progenies from triploid and diploid-triploid crosses. 30 trisomics, 2 double trisomics, 1 tetrasomic, and 2 higher aneuploids were obtained. Some of the aneuploids were found to be different from those reported earlier and higher aneuploids carried eight extra chromosomes. The plants with one extra chromosome occurred more frequently (67%) than the other aneuploid types. The changes in morphological traits such as a reduction in the amount of growth and the size of leaf etc. distinguished aneuploids from diploids. In the higher aneuploids the plant parts were highly exaggerated and pollen sterility was very high. The chromosomal counts in acetocarmine squashes confirmed the presence of extra chromosome(s). Aneuploids particularly trisomics were found to be promising and may lead to the production of commercially viable plants.     

粳稻三体的染色体G—显带鉴定

采用有丝分裂染色体的G-显带技术,对供试的6个三体的额外染色体进行了鉴定。结果表明:A型、B型、C型、D型、E型和H型三体的额外染色体分别为K5、K6、K12、K7、K8和K10。用不同的分裂时期的细胞所鉴定出的结果完全一致。与过去所用的三体鉴定的方法相比较,利用G-显带技术鉴定三体的方法具有准确性高,稳定性和重复性好以及简便易行的优点。     

An asymmetric chromosome pair undergoes synaptic adjustment and crossover redistribution during Caenorhabditis elegans meiosis: implications for sex chromosome evolution

Heteromorphic sex chromosomes, such as the X/Y pair in mammals, differ in size and DNA sequence yet function as homologs during meiosis; this bivalent asymmetry presents special challenges for meiotic completion. In Caenorhabditis elegans males carrying mnT12, an X;IV fusion chromosome, mnT12 and IV form an asymmetric bivalent: chromosome IV sequences are capable of pairing and synapsis, while the contiguous X portion of mnT12 lacks a homologous pairing partner. Here, we investigate the meiotic behavior of this asymmetric neo-X/Y chromosome pair in C. elegans. Through immunolocalization of the axis component HIM-3, we demonstrate that the unpaired X axis has a distinct, coiled morphology while synapsed axes are linear and extended. By showing that loci at the fusion-proximal end of IV become unpaired while remaining synapsed as pachytene progresses, we directly demonstrate the occurrence of synaptic adjustment in this organism. We further demonstrate that meiotic crossover distribution is markedly altered in males with the asymmetric mnT12/+ bivalent relative to controls, resulting in greatly reduced crossover formation near the X;IV fusion point and elevated crossovers at the distal end of the bivalent. In effect, the distal end of the bivalent acts as a neo-pseudoautosomal region in these males. We discuss implications of these findings for mechanisms that ensure crossover formation during meiosis. Furthermore, we propose that redistribution of crossovers triggered by bivalent asymmetry may be an important driving force in sex chromosome evolution.     

Development and applications of a complete set of rice telotrisomics

We previously isolated a complete set of primary trisomics along with many other aneuploids from triploid plants derived from an indica rice variety "Zhongxian 3037." About 30,000 progeny from these trisomic and aneuploid plants were grown each year from 1994 to 1999. The variants that differed morphologically from both the diploids and the original primary trisomics were collected for cytological identification. From these variants, a complete set of telotrisomics covering all 24 rice chromosome arms was obtained. The identities of the extra chromosomes were further confirmed by dosage analysis of the RFLP markers on extra chromosome arms. The telocentric nature of the extra chromosomes in these stocks was verified by fluorescence in situ hybridization (FISH) using a rice centromeric BAC clone as a marker probe. In general, the shorter the extra chromosome arm of a telotrisomic, the stronger the resemblance it bears to the diploid; the longer the extra chromosome arm, the stronger the resemblance to the corresponding primary trisomic. We demonstrated that DNA clones can be rapidly assigned to specific chromosome arms by dosage analysis with the telotrisomics. We also showed that telotrisomics are valuable tools for chromosome microdissection and for developing chromosome-specific DNA markers.     

Behaviour of the ZW sex bivalent in the snake Bothrops jararaca

The behavior of the ZW sex bivalent was investigated in female meiosis of the poisonous snake Bothrops jararaca. The Z is euchromatic and synapses end to end with the W. The W chromosome shows a heterochromatic segment distally in the short arm. Pairing occurs between the long arm of the W and the slightly longer arm of the mediocentric Z. A sex vesicle, similar to the one found in the XY placental mammals, does not occur in snakes. The Z and W chromosomes segregate reductionally in the first meiotic division and equationally in the second.This work is dedicated to the memory of my father Lino Pires de Camargo     

Trisomics from triploid-diploid crosses in self-incompatible Lycopersicum peruvianum

Summary An attempt was carried out to produce trisomics of the wild tomato L. peruvianum, to define their essential features, and to detect relationships between trisomy and the expression of self-compatibility.Triploid-diploid crosses in L. peruvianum yielded nearly 40% aneuploids. Of these, 18% were single trisomics, and the rest had 2, 3 and 4 extra chromosomes. Almost all the trisomics occurred in crosses where the triploid was used as female parent. Vigour and fertility of trisomics were not much different from those of disomics, and morphologically they were very similar.The extra chromosome was identified in three self-compatible trisomic plants through somatic and pachytene chromosome morphology. One of these plants was trisomic for chromosome 1, while the other two were trisomic for chromosome 3. In these trisomics a positive correlation was found between chromosome length and trivalent formation, but no relationship between chromosome length and frequency of laggards was observed.A series of test-crosses revealed that the capacity of the trisomics to produce seed upon selfing always resulted from alterations of the incompatibility phenotype of the style and not from competitive interaction in the pollen. Progeny analyses showed that the self-compatibility features of the trisomics were not transmitted from one generation to the next. The implications of these findings are discussed.This work has been supported by a contract between the European Communities and the CNEN. This publication is contribution no. 1458 from the Biology Division of the European Communities and contribution no. 472 from the Divisione Applicazioni delle Radiazioni del CNEN.     

Tertiary trisomics in pearl millet (Pennisetum typhoides Stapf & Hubb)

Four tertiary trisomic plants are reported here, two of them (Nos. Tr11 and Tr13) from selfed progeny of a triploid Pearl millet and the other two (Nos. 3/12 and 16/7) from the progenies of radiation induced interchange heterozygotes. The extra chromosome in Tr13 and 3/12 was the nucleolus organizing chromosome. In No. 16/7 an extra chromosome enters into an association chromosomes were also involved. Meiotic behaviour in these four trisomics indicates that Tr11 and 3/12 are tertiary trisomics. It is suggested that two reciprocal translocations have occurred between two sets of chromosomes in the triploid parent and that syngamy has taken place in such a way that four interchange chromosomes and one non-interchange nucleolus organizing chromosome have come together in the offspring. The extra chromosome in No. 16/7 is an interchange chromosome which is homologous to one of the chromosomes of an interchange complex of six chromosomes.     

Identification of five new primary simple trisomies in soybean based on pachytene chromosome analysis.

Primary trisomics are ideal cytogenetic tools for associating genes and linkage groups to known chromosomes and testing their independence. In the cultivated soybean, only 8 of the possible 20 primary simple trisomics are known. In this report cytological evidence for the identification of five more new primary simple trisomics, corresponding to chromosomes 6, 8, 12, 16, and 19, is presented for the first time. The precise identification was based on trivalent configuration of chromosomes at the pachynema stage of meiosis, where the chromosomes were identified by their characteristic total length, arm ratio, and distribution of heterochromatin and euchromatin. Cytological observation of chromosome pairing in the 2n = 42 chromosome F1 plants, obtained from eight crosses between known primary trisomics, also supported the identification of primary trisomics in soybean based on pachytene chromosome analysis. Together with the eight primary trisomics identified previously, 13 of the possible 20 primary simple trisomics have been successfully identified, which accounts for about 76% of the total nuclear euchromatin in soybean.     

Evidence for specific RNA/protein interactions in the differential segment of the W sex chromosome in the amphibian Pleurodeles waltl

Pleurodeles exhibits a ZZ/ZW system of GSD (genotype sex determination). However, the Z and W sex chromosomes appear to be morphologically identical. A short RNA sequence is described that was specifically bound to lampbrush loops in the differential segment of the sexual bivalent IV. The distribution of these labeled loops in experimentally produced ZZ and WW females enabled us to demonstrate that such labeled loops were perfectly correlated with the W chromosome. Therefore, this RNA sequence constitutes an excellent marker for the W differential segment. Furthermore, analysis of the labeled loops under various experimental conditions suggested that their labeling is caused by specific interactions between this RNA sequence and lampbrush loop-associated proteins (RNA/protein interactions). North-western assays revealed that nuclear polypeptide(s) of 65 kDa could be responsible for such binding.     

Five primary trisomics from translocation heterozygote progenies in common bean,Phaseolus vulgaris L.

Summary Twelve distinct phenotypic groups of plants were isolated from nondisjunction progenies of 11 translocation heterozygote stocks. All the plants in these phenotypic groups originated in the light weight seed class. Five of the 12 phenotypic groups of plants have been verified as primary trisomics. They are all phenotypically distinguishable from each other and from disomics. One of the five primary trisomic groups, puckered leaf, was directly recovered as a primary trisomic from the original translocation heterozygote progenies. Three of the five trisomics — weak stem, dark green leaf, and convex leaf — originated first as tertiary trisomics. The related primary trisomics were isolated later from progenies of selfed tertiary trisomics. The fifth group, chlorotic leaf, originated at a low frequency among the progenies of three other trisomics: puckered leaf, convex leaf, and dark green leaf. The chlorotic leaf did not set seed under field conditions. The remaining four groups — puckered leaf, dark green leaf, convex leaf, and weak stem — are fertile, though sensitive to high temperature conditions. The transmission rate of the extra chromosome on selfing ranges from 28% to 41%. Physical identification of the extra chromosome has not been achieved for any of the five trisomic groups. Two trisomic groups, dark green leaf and convex leaf, have produced tetrasomics at low frequency. The phenotypes of these two tetrasomics are similar to the corresponding trisomics but more exaggerated.Fla. Agr. Expt. Stn. Journal Series No. 7137     

Non-relationship between nucleolus and sex chromosome system Xyp in Chelymorpha variabilis boheman (Coleoptera: Chrysomelidae)

Nucleolar-organizer region, nucleolus and mode of association of the sex bivalent were analyzed in spermatecytes of Chelymorpha variabilis Boheman. This species (2n=10II+Xy_p) shows the typical sex chromosome system of the group Polyphaga. The results of silver staining techniques showed the nucleolar organizer region localized in a subterminal position of an autosomal bivalent. During meiotic prophase the nucleolus was distinguished with the silver staining and acridine orange fluorescence technique up to diakinesis. The independence of nucleolus and sex bivalent Xy_p during meiosis is demonstrated. The positively silver staining but negatively orange-red material found within the parachute could be involved in the regular co-orientation of both sex chromosomes. After a longer hypotonic treatment, sex bivalents were observed elongated and paired only at one end during the pachytene stage. Along these sex chromosomes, C-bands showed positive blocks located in the pericentromeric and telomeric regions. Heterochromatic association of both sex chromosomes was suggested.     

Meiosis of T70H translocation trisomic male mice

Meiosis of T70H/+, Ts(1¹³)70H translocation trisomic male mice has been studied using C-banded preparations and ³H-thymidine autoradiography of the first meiotic division. Epididymal sperm counts and sperm morphology scores were also collected. As reported earlier, at the first meiotic division the translocation involved chromosomes 1, 13, 13¹ and 1¹³ (twice) formed mainly three multivalent configurations: Chain III+II, CIV+I and CV. — The autoradiographic study indicated an abnormal, precocious spiralization pattern for the chromatin in CIV+I primary spermatocytes. These cells, occurring together with the CIII+II and CV configurations in recognizable groups, usually descending from single spermatogonial stem cells, are delayed through meiotic prophase. Both delay and disturbed chromosome spiralization in these cells are attributed to the uniform association of the univalent (I) chromosome 1¹³ with the sex chromosomes during pachytene. Primary spermatocytes of the CIV+I configuration and those carrying a CV take longer to develop from metaphase I into secondary spermatocytes than does the CIII+II type. — In T70H tertiary trisomics with a similar chromosome imbalance, the majority of primary spermatocytes degenerates during the diakinesis-metaphase I stages of meiosis. Fertility is low in contrast to the translocation trisomics. Comparison between the two types leads to the conclusion, that trisomy per se reduces the size of the testes and that the univalent containing CIV+I primary spermatocytes, contrary to the almost uniformly 1¹³ univalent carrying spermatocytes of the T70H tertiary trisomics are rescued by the neighbouring CIII+II and CV carrying cells to form normal secondary spermatocytes and morphologically normal sperm.