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Karyotype variability in tropical maize sister inbred lines and hybrids compared with KYS standard line.

Mondin M, Santos-Serejo JA, Bertäo MR, Laborda P, Pizzaia D, Aguiar-Perecin ML - Front Plant Sci (2014)

Bottom Line: Somatic chromosomes of a JD line and the commonly used KYS line were compared by FISH in a hybrid of these lines.This suggests that homologous chromosomes could pair through differential degrees of chromatin packaging in homologous arms differing in size.The results contribute to current knowledge of maize global diversity and also raise questions concerning the meiotic pairing of homologous chromosomes possibly differing in their amounts of repetitive DNA.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, Brazil.

ABSTRACT
Maize karyotype variability has been extensively investigated. The identification of maize somatic and pachytene chromosomes has improved with the development of fluorescence in situ hybridization (FISH) using tandemly repeated DNA sequences as probes. We identified the somatic chromosomes of sister inbred lines that were derived from a tropical flint maize population (Jac Duro [JD]), and hybrids between them, using FISH probes for the 180-bp knob repeat, centromeric satellite (CentC), centromeric satellite 4 (Cent4), subtelomeric clone 4-12-1, 5S ribosomal DNA and nucleolus organizing region DNA sequences. The observations were integrated with data based on C-banded mitotic metaphases and conventional analysis of pachytene chromosomes. Heterochromatic knobs visible at pachynema were coincident with C-bands and 180-bp FISH signals on somatic chromosomes, and most of them were large. Variation in the presence of some knobs was observed among lines. Small 180-bp knob signals were invariant on the short arms of chromosomes 1, 6, and 9. The subtelomeric 4-12-1 signal was also invariant and useful for identifying some chromosomes. The centromere location of chromosomes 2 and 4 differed from previous reports on standard maize lines. Somatic chromosomes of a JD line and the commonly used KYS line were compared by FISH in a hybrid of these lines. The pairing behavior of chromosomes 2 and 4 at pachytene stage in this hybrid was investigated using FISH with chromosome-specific probes. The homologues were fully synapsed, including the 5S rDNA and CentC sites on chromosome 2, and Cent4 and subtelomeric 4-12-1 sites on chromosome 4. This suggests that homologous chromosomes could pair through differential degrees of chromatin packaging in homologous arms differing in size. The results contribute to current knowledge of maize global diversity and also raise questions concerning the meiotic pairing of homologous chromosomes possibly differing in their amounts of repetitive DNA.

No MeSH data available.


Somatic karyotypes of JD lines (A–C) and hybrids (D–F), labeled by FISH with probes for the knob 180-bp repeat (A,B,D–F, green), Cent4 (A,B,D,F, red and C, green), subtelomeric 4-12-1 (B,D–F, red), 5S rDNA (C, red and F, pseudo-colored white), CentC (E, green). Note that the large knobs can be detected as DAPI bands in (C) and that the knobless chromosome 9 from the parent 133425, in hybrid 132331 × 133425, has a small 180-bp signal on 9S (D). Chromosomes 2, 3, 5, 7, 8, and 9 from the 441311 parent (placed on the left) can be recognized in the 441311 × KYS hybrid (E,F). The chromosomes were counterstained with DAPI. Scale bar = 10 μm.
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Figure 4: Somatic karyotypes of JD lines (A–C) and hybrids (D–F), labeled by FISH with probes for the knob 180-bp repeat (A,B,D–F, green), Cent4 (A,B,D,F, red and C, green), subtelomeric 4-12-1 (B,D–F, red), 5S rDNA (C, red and F, pseudo-colored white), CentC (E, green). Note that the large knobs can be detected as DAPI bands in (C) and that the knobless chromosome 9 from the parent 133425, in hybrid 132331 × 133425, has a small 180-bp signal on 9S (D). Chromosomes 2, 3, 5, 7, 8, and 9 from the 441311 parent (placed on the left) can be recognized in the 441311 × KYS hybrid (E,F). The chromosomes were counterstained with DAPI. Scale bar = 10 μm.

Mentions: The identification of the C-banded somatic chromosomes was based on their relative lengths and arm ratios (Table 2), and on the knob (C-band) positions. Figure 1 shows the C-banded karyograms of the 441123 and 444331 lines and their hybrid. In the 441123 line (Figure 1A), knobs were observed on chromosomes 3L, 5L, 6L 7SL, 8L, and 9S. In the 444331 line, the knobs on 3L, 7S, and 9S were not present (Figure 1B), and chromosome 7 could be distinguished from chromosome 8 by its larger knob (K7L). In the 441123 × 444331 hybrid (Figure 1C), it can be visualized that in the heterozygous pairs 3, 7, and 9, the presence of the large knob altered the chromosome sizes (Table 2). Chromosomes 2 and 4 were recognized in the C-banded metaphases according to FISH data using the chromosome-specific 5S rDNA probe for chromosome 2 (Mascia et al., 1981) and Cent4 for chromosome 4 (Page et al., 2001), as seen in the metaphase from a 441123 × 442612 hybrid (Figure 1D). The position of the chromosome 2 centromere was submedian in comparison with that of chromosome 4. It is interesting to note that the FISH procedure enhances the visualization of the knob regions, which can be seen as DAPI bands. The knob composition of the 442612 line is shown in Table 1. Chromosome 6 was identified by the NOR rDNA signal (Figure 1E), and by the secondary constriction and satellite on 6S which were visualized in the C-banding and FISH spreads (Figures 1 and 4). In the 132331 and 133425 lines, knobs on 3L and 5L were absent as can be observed in the 132331 × 133425 hybrid, homozygous for knobs at 6L, 7SL, and 8L, and heterozygous for K9S (Figure 1F), which was only observed in 132331 line (Table 1). The values of relative lengths and arm ratios of the somatic chromosomes without knobs (Table 2) were consistent with previous data describing wild maize (Aguiar-Perecin and Vosa, 1985), except for the arm ratios of chromosomes 2 and 4, higher in chromosome 2 (about 1.44) compared with chromosome 4 (about 1.30) in JD lines. The knobless chromosome 5 was analyzed in spreads of the 132331 × 133425 hybrid.


Karyotype variability in tropical maize sister inbred lines and hybrids compared with KYS standard line.

Mondin M, Santos-Serejo JA, Bertäo MR, Laborda P, Pizzaia D, Aguiar-Perecin ML - Front Plant Sci (2014)

Somatic karyotypes of JD lines (A–C) and hybrids (D–F), labeled by FISH with probes for the knob 180-bp repeat (A,B,D–F, green), Cent4 (A,B,D,F, red and C, green), subtelomeric 4-12-1 (B,D–F, red), 5S rDNA (C, red and F, pseudo-colored white), CentC (E, green). Note that the large knobs can be detected as DAPI bands in (C) and that the knobless chromosome 9 from the parent 133425, in hybrid 132331 × 133425, has a small 180-bp signal on 9S (D). Chromosomes 2, 3, 5, 7, 8, and 9 from the 441311 parent (placed on the left) can be recognized in the 441311 × KYS hybrid (E,F). The chromosomes were counterstained with DAPI. Scale bar = 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4195276&req=5

Figure 4: Somatic karyotypes of JD lines (A–C) and hybrids (D–F), labeled by FISH with probes for the knob 180-bp repeat (A,B,D–F, green), Cent4 (A,B,D,F, red and C, green), subtelomeric 4-12-1 (B,D–F, red), 5S rDNA (C, red and F, pseudo-colored white), CentC (E, green). Note that the large knobs can be detected as DAPI bands in (C) and that the knobless chromosome 9 from the parent 133425, in hybrid 132331 × 133425, has a small 180-bp signal on 9S (D). Chromosomes 2, 3, 5, 7, 8, and 9 from the 441311 parent (placed on the left) can be recognized in the 441311 × KYS hybrid (E,F). The chromosomes were counterstained with DAPI. Scale bar = 10 μm.
Mentions: The identification of the C-banded somatic chromosomes was based on their relative lengths and arm ratios (Table 2), and on the knob (C-band) positions. Figure 1 shows the C-banded karyograms of the 441123 and 444331 lines and their hybrid. In the 441123 line (Figure 1A), knobs were observed on chromosomes 3L, 5L, 6L 7SL, 8L, and 9S. In the 444331 line, the knobs on 3L, 7S, and 9S were not present (Figure 1B), and chromosome 7 could be distinguished from chromosome 8 by its larger knob (K7L). In the 441123 × 444331 hybrid (Figure 1C), it can be visualized that in the heterozygous pairs 3, 7, and 9, the presence of the large knob altered the chromosome sizes (Table 2). Chromosomes 2 and 4 were recognized in the C-banded metaphases according to FISH data using the chromosome-specific 5S rDNA probe for chromosome 2 (Mascia et al., 1981) and Cent4 for chromosome 4 (Page et al., 2001), as seen in the metaphase from a 441123 × 442612 hybrid (Figure 1D). The position of the chromosome 2 centromere was submedian in comparison with that of chromosome 4. It is interesting to note that the FISH procedure enhances the visualization of the knob regions, which can be seen as DAPI bands. The knob composition of the 442612 line is shown in Table 1. Chromosome 6 was identified by the NOR rDNA signal (Figure 1E), and by the secondary constriction and satellite on 6S which were visualized in the C-banding and FISH spreads (Figures 1 and 4). In the 132331 and 133425 lines, knobs on 3L and 5L were absent as can be observed in the 132331 × 133425 hybrid, homozygous for knobs at 6L, 7SL, and 8L, and heterozygous for K9S (Figure 1F), which was only observed in 132331 line (Table 1). The values of relative lengths and arm ratios of the somatic chromosomes without knobs (Table 2) were consistent with previous data describing wild maize (Aguiar-Perecin and Vosa, 1985), except for the arm ratios of chromosomes 2 and 4, higher in chromosome 2 (about 1.44) compared with chromosome 4 (about 1.30) in JD lines. The knobless chromosome 5 was analyzed in spreads of the 132331 × 133425 hybrid.

Bottom Line: Somatic chromosomes of a JD line and the commonly used KYS line were compared by FISH in a hybrid of these lines.This suggests that homologous chromosomes could pair through differential degrees of chromatin packaging in homologous arms differing in size.The results contribute to current knowledge of maize global diversity and also raise questions concerning the meiotic pairing of homologous chromosomes possibly differing in their amounts of repetitive DNA.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, Brazil.

ABSTRACT
Maize karyotype variability has been extensively investigated. The identification of maize somatic and pachytene chromosomes has improved with the development of fluorescence in situ hybridization (FISH) using tandemly repeated DNA sequences as probes. We identified the somatic chromosomes of sister inbred lines that were derived from a tropical flint maize population (Jac Duro [JD]), and hybrids between them, using FISH probes for the 180-bp knob repeat, centromeric satellite (CentC), centromeric satellite 4 (Cent4), subtelomeric clone 4-12-1, 5S ribosomal DNA and nucleolus organizing region DNA sequences. The observations were integrated with data based on C-banded mitotic metaphases and conventional analysis of pachytene chromosomes. Heterochromatic knobs visible at pachynema were coincident with C-bands and 180-bp FISH signals on somatic chromosomes, and most of them were large. Variation in the presence of some knobs was observed among lines. Small 180-bp knob signals were invariant on the short arms of chromosomes 1, 6, and 9. The subtelomeric 4-12-1 signal was also invariant and useful for identifying some chromosomes. The centromere location of chromosomes 2 and 4 differed from previous reports on standard maize lines. Somatic chromosomes of a JD line and the commonly used KYS line were compared by FISH in a hybrid of these lines. The pairing behavior of chromosomes 2 and 4 at pachytene stage in this hybrid was investigated using FISH with chromosome-specific probes. The homologues were fully synapsed, including the 5S rDNA and CentC sites on chromosome 2, and Cent4 and subtelomeric 4-12-1 sites on chromosome 4. This suggests that homologous chromosomes could pair through differential degrees of chromatin packaging in homologous arms differing in size. The results contribute to current knowledge of maize global diversity and also raise questions concerning the meiotic pairing of homologous chromosomes possibly differing in their amounts of repetitive DNA.

No MeSH data available.