scholarly journals The unusualdRempretrotransposon is abundant, highly mutagenic, and mobilized only in the second pollen mitosis of some maize lines

2020 ◽  
Vol 117 (30) ◽  
pp. 18091-18098
Author(s):  
Qinghua Wang ◽  
Jun Huang ◽  
Yubin Li ◽  
Hugo K. Dooner
Keyword(s):  
Spontaneous Mutation ◽  
Male Meiosis ◽  
Normal Embryo ◽  
Ltr Retrotransposons ◽  
Pollen Mitosis ◽  
Low Copy Number ◽  
Frequent Mutations ◽  
Second Pollen Mitosis ◽  
Mutant Phenotypes ◽  
Insertion Mutants

The frequent mutations recovered recently from the pollen of select maize lines resulted from the meiotic mobilization of specific low-copy number long-terminal repeat (LTR) retrotransposons, which differ among lines. Mutations that arise at male meiosis produce kernels with concordant mutant phenotypes in both endosperm and embryo because the two sperms that participate in double fertilization are genetically identical. Those are in a majority. However, a small minority of kernels with a mutant endosperm carry a nonconcordant normal embryo, pointing to a postmeiotic or microgametophytic origin. In this study, we have identified the basis for those nonconcordant mutations. We find that all are produced by transposition of a defective LTR retrotransposon that we have termeddRemp(defective retroelement mobile in pollen). This element has several unique properties. Unlike the mutagenic LTR retrotransposons identified previously,dRempis present in hundreds of copies in all sequenced lines. It seems to transpose only at the second pollen mitosis because alldRempinsertion mutants are nonconcordant yet recoverable in either the endosperm or the embryo. Although it does not move in most lines,dRempis highly mobile in the Corn Belt inbred M14, identified earlier by breeders as being highly unstable. Lastly, it can be recovered in an array of structures, ranging from solo LTRs to tandemdRemprepeats containing several internal LTRs, suggestive of extensive recombination during retrotransposition. These results shed further light on the spontaneous mutation process and on the possible basis for inbred instability in maize.

scholarly journals Spontaneous mutations in maize pollen are frequent in some lines and arise mainly from retrotranspositions and deletions

2019 ◽  
Vol 116 (22) ◽  
pp. 10734-10743 ◽  
Author(s):  
Hugo K. Dooner ◽  
Qinghua Wang ◽  
Jun T. Huang ◽  
Yubin Li ◽  
Limei He ◽  
...  
Keyword(s):  
Copy Number ◽  
Large Scale ◽  
High Throughput Sequencing ◽  
Ltr Retrotransposons ◽  
Spontaneous Mutations ◽  
Maize Pollen ◽  
Genome Wide ◽  
Autonomous Element ◽  
Low Copy Number ◽  
Female Germline

While studying spontaneous mutations at the maizebronze(bz) locus, we made the unexpected discovery that specific low-copy number retrotransposons are mobile in the pollen of some maize lines, but not of others. We conducted large-scale genetic experiments to isolate newbzmutations from severalBzstocks and recovered spontaneous stable mutations only in the pollen parent in reciprocal crosses. Most of the new stablebzmutations resulted from either insertions of low-copy number long terminal repeat (LTR) retrotransposons or deletions, the same two classes of mutations that predominated in a collection of spontaneouswxmutations [Wessler S (1997)The Mutants of Maize, pp 385–386]. Similar mutations were recovered at the closely linkedshlocus. These events occurred with a frequency of 2–4 × 10−5in two lines derived from W22 and in 4Co63, but not at all in B73 or Mo17, two inbreds widely represented in Corn Belt hybrids. Surprisingly, the mutagenic LTR retrotransposons differed in the active lines, suggesting differences in the autonomous element make-up of the lines studied. Some active retrotransposons, likeHopscotch,Magellan, andBs2, aBs1variant, were described previously; others, likeFotoandFocouin 4Co63, were not. By high-throughput sequencing of retrotransposon junctions, we established that retrotranposition ofHopscotch,Magellan, andBs2occurs genome-wide in the pollen of active lines, but not in the female germline or in somatic tissues. We discuss here the implications of these results, which shed light on the source, frequency, and nature of spontaneous mutations in maize.

Extrême précocité et conditions thermiques du développement apical et floral chez Claytonia caroliniana var. caroliniana

1985 ◽  
Vol 63 (9) ◽  
pp. 1516-1520 ◽  
Author(s):  
Miroslav M. Grandtner ◽  
Camille Gervais
Keyword(s):  
Sugar Maple ◽  
Floral Development ◽  
Growth Period ◽  
Chromosomal Anomalies ◽  
Cellular Activity ◽  
Seed Setting ◽  
Pollen Mitosis ◽  
Aerial Portion ◽  
Second Pollen Mitosis ◽  
First Pollen Mitosis

The apical and floral development of Claytonia caroliniana var. caroliniana has been studied concurrently with soil temperature, in a sugar maple forest of the Stoneham mountain, Québec. Apical cellular activity begins early in May, while the flowering stems of the year are present. At the beginning of July, external apical development becomes visible. In the first days of August, 9 months before flowering, the foliar and floral structures of the next year are already present in the soil. Meiosis takes place at the beginning of October and first pollen mitosis follows shortly after, in the middle of the same month. From that time, well developed individuals, without chlorophyll, are present just under the litter. They can occasionally turn green and reach the upper surface of the litter in November or December, where they will spend wintertime under the snow, at a temperature oscillating between 0 and −4 °C. This behaviour is quite close to the survival strategy of hemicryptophytes. The active epigeous growth period begins in the middle of April, with the melting of snow. Second pollen mitosis and flowering take place at this time, rapidly followed by seed setting, dissemination, and destruction of the aerial portion of the plant. Cytoecological investigations to study possible influence of environmental factors on chromosomal anomalies in primordia should thus be conducted during the year preceding the flowering of Claytonia.

scholarly journals B CHROMOSOME NONDISJUNCTION IN CORN: CONTROL BY FACTORS NEAR THE CENTROMERE

Genetics ◽  
1981 ◽  
Vol 97 (2) ◽  
pp. 379-389
Author(s):  
Wayne R Carlson ◽  
Tau-San Chou
Keyword(s):  
B Chromosome ◽  
B Chromosomes ◽  
Translocation Chromosome ◽  
Pollen Mitosis ◽  
Second Pollen Mitosis ◽  
Chromosome Nondisjunction

ABSTRACT B chromosomes of corn are stable at all mitotic and meiotic divisions of the plant except the second pollen mitosis. In the latter division, B chromosomes undego mitotic nondisjunction at rates as high as 98%. Studies by several workers on B-A translocation chromosomes have provided evidence for the existence of four factors on the B chromosome that control nondisjunction and are separable from the centromere. Two of these factors, referred to here as factors 3 and 4, flank the B chromosome centromere. Factor 3 is the centromere-adjacent heterochromatin in the long arm of the B chromosome; factor 4 is located in the minute short arm. Evidence is presented here supporting the existence of factors 3 and 4. Deficiencies that include each factor were identified following centromeric misdivision events, with breaks at or near the centromere of a B-translocation chromosome. B chromosomes lacking factors 3 or 4 show much less nondisjunction than do chromosomes containing them. The possible function of factor 4 in nondisjuntion is also discussed.

scholarly journals The Gametic Non-Lethal Gene Gal on Chromosome 5 Is Indispensable for the Transmission of the Co-Induced Semidwarfing Gene d60 in Rice

Biology ◽  
2019 ◽  
Vol 8 (4) ◽  
pp. 94
Author(s):  
Motonori Tomita ◽  
Takatoshi Tanisaka
Keyword(s):  
Genetic Model ◽  
Recessive Gene ◽  
Male Gamete ◽  
Lethal Gene ◽  
Single Recessive Gene ◽  
Pollen Mitosis ◽  
Chromosome 5 ◽  
Second Pollen Mitosis ◽  
Generation Sequencing ◽  
Simple Sequence

The gametic lethal gene gal in combination with the semidwarfing gene d60 causes complementary lethality in rice. Here, we attempted to ascertain the existence of gal and clarify male gamete abortion caused by d60 and gal. Through the F2 to F4 generations derived from the cross between D60gal-homozygous and d60Gal-homozygous, progenies of the partial sterile plants (D60d60Galgal) were segregated in a ratio of 1 semidwarf (1 d60d60GalGal):2 tall and quarter sterile (2 D60d60Galgal):6 tall (2 D60d60GalGal:1 D60D60GalGal:2 D60D60Galgal:1 D60D60galgal), which is skewed from the Mendelian ratio of 1 semidwarf:3 tall. However, the F4 generation was derived from fertile and tall heterozygous F2 plants (D60d60GalGal), which were segregated in the Mendelian ratio of 1[semidwarf (d60d60GalGal)]:2[1 semidwarf:3 tall (D60d60GalGal)]:1[tall (D60D60GalGal)]. The backcrossing of D60Gal-homozygous tall F4 plants with Hokuriku 100 resulted in fertile BCF1 and BCF2 segregated in a ratio of 1 semidwarf:3 tall, proving that d60 is inherited as a single recessive gene in the D60d60GalGal genetic background (i.e., in the absence of gal). Further, gal was localized on chromosome 5, which is evident from the deviated segregation of d1 as 1:8 and linkage with simple sequence repeat (SSR) markers. Next-generation sequencing identified the candidate SNP responsible for Gal. In F1 and sterile F2, at the binucleate stage, partial pollen discontinued development. Degraded pollen lost vegetative nuclei, but second pollen mitosis raising two generative nuclei was observed. Thus, our study describes a novel genetic model for a reproductive barrier. This is the first report on such a complementary lethal gene, whose mutation allows the transmission of a co-induced valuable semidwarfing gene d60.

Unstable inheritance of maize B-type chromosomes that lack centric heterochromatin

Genome ◽  
2006 ◽  
Vol 49 (5) ◽  
pp. 420-431 ◽  
Author(s):  
Wayne R Carlson
Keyword(s):  
B Chromosome ◽  
Chromosome 9 ◽  
Pollen Mitosis ◽  
Genetic Studies ◽  
Telocentric Chromosome ◽  
Deletion Derivative ◽  
Translocation Heterozygote ◽  
Second Pollen Mitosis

The B chromosome of maize undergoes frequent non-disjunction at the second pollen mitosis. In B–A translocations, the B–A chromosome retains the capacity for non-disjunction. We have collected deletion-derivative TB-9Sb stocks. One derivative, the "type 1 telocentric", has a B–9 chromosome that lacks centric heterochromatin. It produces few recessive (non-disjunctional) phenotypes in pollen parent testcrosses of the translocation heterozygote, 9 9–B telo B–9. The finding helped demonstrate the role of centric heterochromatin in non-disjunction. An isochromo some derivative of the type 1 telocentric was also recovered. It was tested in the 9–B 9–B iso B–9 constitution. This is equivalent to 9 9–B telo B–9 in terms of chromosome 9 dosage. Surprisingly, crosses with the isochromosome gave significant levels of recessive phenotypes. In addition, high levels of variegated phenotypes were found. Recently, a circumstance was found that makes inheritance of the type 1 telocentric chromosome somewhat similar to that of the isochromosome. Crosses with hypoploid 9–B 9–B telo B–9 plants showed significant levels of recessive and variegated phenotypes. These crosses were investigated to help explain the source(s) of the phenotypes. Cytological and genetic studies were performed. Centric misdivision was found to account for the variegated phenotypes. A mixture of conventional B non-disjunction and centric misdivision produced the recessive phenotypes. The significance of conventional non-disjunction in the absence of centric heterochromatin is discussed.Key words: cytogenetics, B chromosome, centromere, maize.

Locating a site on the maize B chromosome that controls preferential fertilization

Genome ◽  
2007 ◽  
Vol 50 (6) ◽  
pp. 578-587 ◽  
Author(s):  
Wayne R. Carlson
Keyword(s):  
B Chromosome ◽  
B Chromosomes ◽  
Chromosome 9 ◽  
Chromosome Deletion ◽  
Pollen Mitosis ◽  
Preferential Fertilization ◽  
Second Pollen Mitosis ◽  
A Site ◽  
Derivatives Of

In maize, the B chromosome can undergo nondisjunction at the second pollen mitosis, producing sperm with two B chromosomes and sperm with zero B chromosomes. Preferential fertilization is the ability of the sperm carrying two B chromosomes to transmit more frequently to the embryo of a kernel than the sperm lacking the B chromosome. A translocation involving the B chromosome and chromosome 9, TB-9Sb, has been used to study preferential fertilization. The B-9 chromosome has the same properties of nondisjunction and preferential fertilization as the standard B chromosome. Deletion derivatives of B-9, which lack the centric heterochromatin and possibly some adjacent euchromatin, were tested for their ability to induce preferential fertilization. They were found to lack the capacity for preferential fertilization.

scholarly journals Genetic Dissection of Meiotic Cytokinesis in Drosophila Males

2004 ◽  
Vol 15 (5) ◽  
pp. 2509-2522 ◽  
Author(s):  
Maria Grazia Giansanti ◽  
Rebecca M. Farkas ◽  
Silvia Bonaccorsi ◽  
Dan L. Lindsley ◽  
Barbara T. Wakimoto ◽  
...  
Keyword(s):  
Male Meiosis ◽  
Genetic Dissection ◽  
Male Sterile ◽  
Large Size ◽  
Wheel Drive ◽  
A Cell ◽  
Cell Type Specific ◽  
Meiotic Spindles ◽  
Mutant Phenotypes ◽  
Four Wheel Drive

We have used Drosophila male meiosis as a model system for genetic dissection of the cytokinesis mechanism. Drosophila mutants defective in meiotic cytokinesis can be easily identified by their multinucleate spermatids. Moreover, the large size of meiotic spindles allows characterization of mutant phenotypes with exquisite cytological resolution. We have screened a collection of 1955 homozygous mutant male sterile lines for those with multinucleate spermatids, and thereby identified mutations in 19 genes required for cytokinesis. These include 16 novel loci and three genes, diaphanous, four wheel drive, and pebble, already known to be involved in Drosophila cytokinesis. To define the primary defects leading to failure of cytokinesis, we analyzed meiotic divisions in male mutants for each of these 19 genes. Examination of preparations stained for tubulin, anillin, KLP3A, and F-actin revealed discrete defects in the components of the cytokinetic apparatus, suggesting that these genes act at four major points in a stepwise pathway for cytokinesis. Our results also indicated that the central spindle and the contractile ring are interdependent structures that interact throughout cytokinesis. Moreover, our genetic and cytological analyses provide further evidence for a cell type-specific control of Drosophila cytokinesis, suggesting that several genes required for meiotic cytokinesis in males are not required for mitotic cytokinesis.

scholarly journals De novo centromere formation on chromosome fragments with an inactive centromere in maize (Zea mays)

2021 ◽  
Author(s):  
Ryan N. Douglas ◽  
Hua Yang ◽  
Bing Zhang ◽  
Chen Chen ◽  
Fangpu Han ◽  
...  
Keyword(s):  
De Novo ◽  
Low Frequency ◽  
B Chromosome ◽  
Chromosome 9 ◽  
Centromere Region ◽  
Pollen Mitosis ◽  
Accumulation Mechanism ◽  
Chromosome Fragments ◽  
Breakpoint Determination ◽  
Second Pollen Mitosis

AbstractThe B chromosome of maize undergoes nondisjunction at the second pollen mitosis as part of its accumulation mechanism. Previous work identified 9-Bic-1 (9-B inactivated centromere-1), which comprises an epigenetically silenced B chromosome centromere that was translocated to the short arm of chromosome 9(9S). This chromosome is stable in isolation, but when normal B chromosomes are added to the genotype, it will attempt to undergo nondisjunction during the second pollen mitosis and usually fractures the chromosome in 9S. These broken chromosomes allow a test of whether the inactive centromere is reactivated or whether a de novo centromere is formed elsewhere on the chromosome to allow recovery of fragments. Breakpoint determination on the B chromosome and chromosome 9 showed that mini chromosome B1104 has the same breakpoint as 9-Bic-1 in the B centromere region and includes a portion of 9S. CENH3 binding was found on the B centromere region and on 9S, suggesting both centromere reactivation and de novo centromere formation. Another mini chromosome, B496, showed evidence of rearrangement, but it also only showed evidence for a de novo centromere. Other mini chromosome fragments recovered were directly derived from the B chromosome with breakpoints concentrated near the centromeric knob region, which suggests that the B chromosome is broken at a low frequency due to the failure of the sister chromatids to separate at the second pollen mitosis. Our results indicate that both reactivation and de novo centromere formation could occur on fragments derived from the progenitor possessing an inactive centromere.

scholarly journals Dynamics of R1 and R2 Elements in the rDNA Locus of Drosophila simulans

Genetics ◽  
2001 ◽  
Vol 158 (4) ◽  
pp. 1557-1567 ◽  
Author(s):  
César E Pérez-González ◽  
Thomas H Eickbush
Keyword(s):  
Copy Number ◽  
Rdna Locus ◽  
Drosophila Simulans ◽  
Rrna Gene ◽  
Ltr Retrotransposons ◽  
Pcr Assay ◽  
X Chromosomes ◽  
Low Copy Number ◽  
The Many ◽  
The Individual

Abstract The mobile elements R1 and R2 insert specifically into the rRNA gene locus (rDNA locus) of arthropods, a locus known to undergo concerted evolution, the recombinational processes that preserve the sequence homogeneity of all repeats. To monitor how rapidly individual R1 and R2 insertions are turned over in the rDNA locus by these processes, we have taken advantage of the many 5′ truncation variants that are generated during the target-primed reverse transcription mechanism used by these non-LTR retrotransposons for their integration. A simple PCR assay was designed to reveal the pattern of the 5′ variants present in the rDNA loci of individual X chromosomes in a population of Drosophila simulans. Each rDNA locus in this population was found to have a large, unique collection of 5′ variants. Each variant was present at low copy number, usually one copy per chromosome, and was seldom distributed to other chromosomes in the population. The failure of these variants to spread to other units in the same rDNA locus suggests a strong recombinational bias against R1 and R2 that results in the individual copies of these elements being rapidly lost from the rDNA locus. This bias suggests a significantly higher frequency of R1 and R2 retrotransposition than we have previously suggested.

Time Course Study of the Chromosome-Type Breakage-Fusion-Bridge Cycle in Maize

Genetics ◽  
1999 ◽  
Vol 153 (3) ◽  
pp. 1435-1444
Author(s):  
Yin-Zhou Zheng ◽  
Robin R Roseman ◽  
Wayne R Carlson
Keyword(s):  
Time Course ◽  
B Chromosome ◽  
Developmental Time ◽  
Chromosome 9 ◽  
Pollen Mitosis ◽  
Chromosome Type ◽  
Root Cells ◽  
Wide Range ◽  
Time Course Study ◽  
Second Pollen Mitosis

Abstract The B chromosome of maize has been used in a study of dicentric chromosomes. TB-9Sb is a translocation between the B and chromosome 9. The B-9 of TB-9Sb carries 60% of the short arm of 9. For construction of dicentrics, a modified B-9 chromosome was used, B-9-Dp9. It consists of the B-9 chromosome plus a duplicated 9S region attached to the distal end. In meiosis, fold-back pairing and crossing over in the duplicated region gives a chromatid-type dicentric B-9 that subsequently initiates a chromatid-type breakage-fusion-bridge cycle. In the male, it forms a single bridge in anaphase II of meiosis and at the first pollen mitosis. However, the cycle is interrupted by nondisjunction of the B centromere at the second pollen mitosis, which sends the B-9 dicentric to one pole and converts it from a chromatid dicentric to a chromosome dicentric. As expected, the new dicentric undergoes the chromosome-type breakage-fusion-bridge cycle and produces double bridges. A large number of plants with chromosome dicentrics were produced in this way. The presence of double bridges in the root cells of plants with a chromosome dicentric was studied during the first 10 wk of development. It was found that the number of plants and cells showing double bridges declined steadily over the 10-wk period. Several lines of evidence indicate that there was no specific developmental time for dicentric loss. “Healing” of broken chromosomes produced by dicentric breakage accounted for much of the dicentric loss. Healing produced a wide range of derived B-9 chromosomes, some large and some small. A group of minichromosomes found in these experiments probably represents the small end of the scale for B-9 derivatives.

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