| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Genetics, Vol. 169, 1169-1173, February 2005, Copyright © 2005
doi:10.1534/genetics.104.035980
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||




,1
* Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, Texas 77843
Department of Horticulture, Texas A&M University, College Station, Texas 77843
USDA-ARS, Southern Plains Agricultural Research Center, College Station, Texas 77845
Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843
1 Corresponding author: Department of Soil and Crop Sciences, Texas A&M University, 370 Olsen Blvd., College Station, TX 77843-2474.
E-mail: stelly{at}tamu.edu
| ABSTRACT |
|---|
|
|
|---|
Here, we used FISH-based karyotyping in concert with analysis of chromosome lengths, arm lengths, and arm ratios to establish a size-based nomenclature for sorghum chromosomes. The ability to reliably identify contracted chromosomes facilitated development of a standardized karyotype (ideogram) for Sorghum bicolor (L.) Moench. The results enabled us to align and orientate the linkage maps relative to the 10 chromosome pairs, and to develop nomenclatures for chromosomes and linkage groups that are based on sorghum chromosome size.
| MATERIALS AND METHODS |
|---|
|
|
|---|
-monobromonaphthalene for 2 hr and then fixed and processed for slide making as described previously (KIM et al. 2002). Prior to FISH, chromosomal DNA on slides was denatured at 70° in 100 µl of 70% formamide in 2x SSC on a hot block for 1.5 min followed by dehydration in 70% ethanol at 20° and 85, 95, and 100% ethanol at room temperature, respectively. For single-probe FISH, the hybridization mixture (25 µl) contained 10 ng of labeled BAC probe DNA, 50% formamide, 10% dextran sulfate, and 2x SSC. The mixture was denatured at 90° for 10 min, chilled on ice, and added to the slide. For FISH of the multi-probe cocktail from 17 BAC clones, 50x Cot-1 DNA was added to the probe mixture, which was denatured at 90° for 10 min, chilled on ice, and then annealed for 30 min before application to the slide. Following overnight incubation at 37°, slides were rinsed at 40° for 5 min in a series of washes consisting of 2x SSC, 50% formamide in 2x SSC, 2x SSC, and 4x SSC plus 0.2% Tween 20, respectively. Images were taken from an Olympus AX-70 epifluorescence microscope (Olympus America, Melville, NY) equipped with standard filter cubes, a Peltier-cooled monochrome 1.3 megapixel Sensys camera (Photometrics, Tucson, AZ), and MacProbe v.4.2.3 digital imaging system (Applied Imaging, San Jose, CA). Homologous chromosome pairs were identified with the aid of MacProbe v.4.2.3, according to the pattern of signal on each chromosome. For karyotyped images, DAPI-stained chromosomes were measured using Optimas v6.0 (Media Cybernetics, Silver Spring, MD). The centromere for each chromatid was identified by the primary constriction and also by FISH of the centromere-associated sequence pCEN38 (ZWICK et al. 2000). FISH-identified chromatid arms were measured and averaged to determine the length for each arm of the genome. The arm ratio (average long arm/short arm ratio), total chromosome length (short arm + long arm), and relative chromosome length (length of the individual chromosome/total length of all chromosomes in the genome) were calculated for each chromosome in the complement. Data were exported to a spreadsheet (Microsoft Excel) and analyzed.
| RESULTS AND DISCUSSION |
|---|
|
|
|---|
|
|
|
The karyotype of BTx623 is grossly similar to those of other sorghum accessions and cultivars (MAGOON and SHAMBULINGAPPA 1960; MAGOON and RAMANA 1961; MAGOON et al. 1964; BENNETT and LAURIE 1995; SANG and LIANG 2000). BTx623 contained an exceptionally long pair of chromosomes, SBI-01, eight pairs of metacentric chromosomes closely graded in size, SBI-02, -03, -04, -05, -07, -08, -09, and -10, and one pair of midsized submetacentric chromosomes, SBI-06. SBI-01 is morphologically the most distinct chromosome of the sorghum haploid complement. In addition to its distinctive length (5.11 µm), SBI-01 is one of only two submetacentric pairs and is the only "satellite" chromosome. Lengths of the remaining chromosomes followed a somewhat bimodal distribution, with SBI-02, -03, -04, and -05 constituting the group of longer chromosomes (3.873.44 µm) and SBI-06, -07, -08, -09, and -10 constituting the group of shorter ones (3.152.97 µm).
The only secondary constriction and nucleolus organizing region (NOR) observed in BTx623 was located near the centromere in the short arm of chromosome 1, SBI-01p. It should be noted, however, that the relative length of the two SBI-01 arms shifts during the mitotic chromosome contraction. Because NORs contract differentially late in the cell cycle and are otherwise very long, overall length of the NOR-bearing arm, SBI-01p, actually exceeds that of the long arm (SBI-01q) until the chromatin contraction process is nearly complete, i.e., at metaphase. Thus, the designation of relative arm sizes at metaphase should connote relative molecular size as well.
In most higher eukaryotes, NORs are situated in short arms of subacrocentric or submetacentric chromosomes. The medial position seen in BTx623 is of interest, but not unique. NORs in most S. bicolor genotypes (and a number of other Sorghum species) occur in medial locations of the largest chromosome of the genome (MAGOON and SHAMBULINGAPPA 1960; MAGOON and RAMANA 1961; MAGOON et al. 1964; BENNETT and LAURIE 1995; SANG and LIANG 2000). However, a temporary constriction occurs in the fifth largest chromosome of a variety of S. bicolor cultivated for silage, in addition to the major constriction in its largest chromosome (GU et al. 1984). The NOR of S. bicolor Combine Kafir 60 is located in the middle of the fifth longest chromosome (YU et al. 1991). The NOR of its close rhizomatous relative, S. propinquum, is located in the short arm of the smallest chromosome (MAGOON and SHAMBULINGAPPA 1961). Such structural differences between parents can complicate linkage analysis (e.g., see BOWERS et al. 2003) and undermine the applicability of each linkage map beyond the respective parental combination.
We developed an integrated "cyto-genomic" map from FISH data on 24 BACs containing linkage markers from across the sorghum genome (Figure 2, Table 2). The centromere position of each chromosome was identified using the centromere-specific probe pCEN38, as previously described by ISLAM-FARIDI et al. (2002; data not shown). Relative to the karyotyping convention (shorter arms at top), the orientations of linkage groups were concordant for SBI-01, -02, -04, -05, -06, -07, and -10, but inverted for SBI-03, -08, and -09 (Figure 2).
|
| ACKNOWLEDGEMENTS |
|---|
|
|
|---|
| LITERATURE CITED |
|---|
|
|
|---|
ANDERSON, L. K., G. G. DOYLE, B. BRIGHAM, J. CARTER, K. D. HOOKER et al., 2003 High-resolution crossover maps for each bivalent of Zea mays using recombination nodules. Genetics 165: 849865.
BENNETT, M. D., and D. A. LAURIE, 1995 Chromosome size in maize and sorghum using EM serial section reconstruction nuclei. Maydica 40: 199204.
BHATTRAMAKKI, D., J. DONG, K. CHHABRA and G. E. HART, 2000 An integrated SSR and RFLP linkage map of Sorghum bicolor (L.) Moench. Genome 43: 9881002.[Medline]
BOIVIN, K., M. DEU, J-F. RAMI, G. TROUCHE and P. HAMON, 1999 Towards a saturated sorghum map using RFLP and AFLP markers. Theor. Appl. Genet. 98: 320328.[CrossRef]
BOWERS, J. E., C. ABBEY, S. ANDERSON, C. CHANG, X. DRAYE et al., 2003 A high-density genetic recombination map of sequence-tagged sites for Sorghum, as a framework for comparative structural and evolutionary genomics of tropical grains and grasses. Genetics 165: 367386.
CHENG, Z., C. R. BUELL, R. A. WING, M. GU and J. JIANG, 2001 Toward a cytological characterization of the rice genome. Genome Res. 11: 21332141.
CHITTENDEN, L. M., K. F. SCHERTZ, Y.-R. LIN, R. A. WING and A. H. PATERSON, 1994 A detailed RFLP map of Sorghum bicolor x S. propinquum, suitable for high-density mapping, suggests ancestral duplication of Sorghum chromosomes or chromosomal segments. Theor. Appl. Genet. 87: 925933.
CRASTA, O. R., W. W. XU, D. T. ROSENOW, J. MULLET and H. T. NGUYEN, 1999 Mapping of post-flowering drought resistance traits in grain sorghum: association between QTLs influencing premature senescence and maturity. Mol. Gen. Genet. 262: 579588.[CrossRef][Medline]
DUFOUR, P., M. DEU, L. GRIVET, A. D'HONT, F. PAULET et al., 1997 Construction of a composite sorghum genome map and comparison with sugarcane, a related complex polyploid. Theor. Appl. Genet. 94: 409418.[CrossRef]
FRANSZ, P. F., S. ARMSTRONG, C. ALONSO-BLANCO, T. C. FISCHER, R. A. TORRES-RUIZ et al., 1998 Cytogenetics for the model system Arabidopsis thaliana. Plant J. 13: 867876.[CrossRef][Medline]
GU, M. H., H. T. MA and G. H. LIANG, 1984 Karyotype analysis of seven species in the genus Sorghum. J. Hered. 75: 196202.
HAUSSMANN, B. I. G., D. E. HESS, N. SEETHARAMA, H. G. WELZ and H. H. GEIGER, 2002 Construction of a combined sorghum linkage map from two recombinant inbred populations using AFLP, SSR, RFLP, and RAPD markers, and comparison with other sorghum maps. Theor. Appl. Genet. 105: 629637.[CrossRef][Medline]
HOWELL, E. C., G. C. BARKER, G. H. JONES, M. J. KEARSEY, G. J. KING et al., 2002 Integration of the cytogenetic and genetic linkage maps of Brassica oleracea. Genetics 161: 12251234.
ISLAM-FARIDI, M. N., K. L. CHILDS, P. E. KLEIN, G. HODNETT, M. A. MENZ et al., 2002 A molecular cytogenetic map of sorghum chromosome 1: fluorescence in situ hybridization analysis with mapped bacterial artificial chromosomes. Genetics 161: 345353.
KIM, J.-S., K. L. CHILDS, M. N. ISLAM-FARIDI, M. A. MENZ, R. R. KLEIN et al., 2002 Integrated karyotyping of sorghum by in situ hybridization of landed BACs. Genome 45: 402412.[Medline]
KLEIN, P. E., R. R. KLEIN, S. W. CARTINHOUR, P. E. ULANCH, J. DONG et al., 2000 A high-throughput AFLP-based method for constructing integrated genetic and physical maps: progress toward a sorghum genome map. Genome Res. 10: 789807.
KONG, L., J. DONG and G. E. HART, 2000 Characteristics, linkage-map positions, and allelic differentiation of Sorghum bicolor (L.) Moench DNA simple-sequence repeats (SSRs). Theor. Appl. Genet. 101: 438448.[CrossRef]
KULIKOVA, O., G. GUALTIERI, R. GEURTS, D.-J. KIM, D. COOK et al., 2001 Integration of the FISH pachytene and genetic maps of Medicago truncatula. Plant J. 27: 4958.[CrossRef][Medline]
KüNZEL, G., L. KORZUN and A. MEISTER, 2000 Cytologically integrated physical restriction fragment length polymorphism maps for the barley genome based on translocation breakpoints. Genetics 154: 397412.
MAGOON, M. L., and M. S. RAMANA, 1961 Cytology of some "Eu-sorghums." Genet. Iber. 13: 129144.
MAGOON, M. L., and K. G. SHAMBULINGAPPA, 1960 Karyomorphological studies in Sorghum ankolib var. annalib red, a Eu-Sorghum. Indian J. Genet. 20: 166177.
MAGOON, M. L., and K. G. SHAMBULINGAPPA, 1961 Karyomorphology of Sorghum propinquum and its bearing on the origin of 40-chromosome sorghum. Chromosoma 42: 460465.[CrossRef]
MAGOON, M. L., P. L. MANCHANDA and M. S. RAMANA, 1964 Cytological and morphological studies in the genus Sorghum. Cytologia 29: 4260.[Medline]
MENZ, M. A., R. R. KLEIN, J. E. MULLET, J. A. OBERT, N. C. UNRUH et al., 2002 A high-density genetic map of Sorghum bicolor (L.) Moench based on 2926 AFLP, RFLP and SSR markers. Plant Mol. Biol. 48: 483499.[CrossRef][Medline]
MING, R., S. C. LIU, J. DA SILVA, W. WILSON, D. BRAGA et al., 1998 Detailed alignment of Saccharum and Sorghum chromosomes: comparative organization of closely related diploid and polyploid genomes. Genetics 150: 16631682.
PENG, Y., K. F. SCHERTZ, S. CARTINHOUR and G. E. HART, 1999 Comparative genome mapping of Sorghum bicolor (L.) Moench using an RFLP map constructed in a population of recombinant inbred lines. Plant Breed. 118: 225235.[CrossRef]
PEREIRA, M. G., M. LEE, P. BRAMEL-COX, W. WOODMAN, J. DOEBLEY et al., 1994 Construction of an RFLP map in sorghum and comparative mapping in maize. Genome 37: 236243.
PRICE, H. J., S. L. DILLON, G. HODNETT, W. ROONEY, L. ROSS et al., 2005 Genome evolution in the genus Sorghum (Poaceae). Ann. Bot. 95: 219227.
SANG, Y., and G. H. LIANG, 2000 Comparative physical mapping of the 18S5.8S- 26rDNA in three sorghum species. Genome 43: 918922.[Medline]
TAO, Q., and H. B. ZHANG, 1998 Cloning and stable maintenance of DNA fragments over 300 kb in Escherichia coli with conventional plasmid-based vectors. Nucleic Acids Res. 26: 49014909.
TAO, Y. Z., D. R. JORDAN, R. G. HENZELL and C. L. MCINTYRE, 1998 Construction of a genetic map in a sorghum RIL population using probes from different sources and its comparison with other sorghum maps. Aust. J. Agric. Res. 49: 729736.
TAO, Y. Z., R. G. HENZELL, D. R. JORDAN, D. G. BUTLER, A. M. KELLY et al., 2000 Identification of genomic regions associated with stay green in sorghum by testing RILs in multiple environments. Theor. Appl. Genet. 100: 12251232.[CrossRef]
WERNER, J. E., T. R. ENDO and B. S. GILL, 1992 Toward a cytogenetically based physical map of the wheat genome. Proc. Natl. Acad. Sci. USA 89: 1130711311.
WHITKUS, R., J. DOEBLEY and M. LEE, 1992 Comparative genome mapping of sorghum and maize. Genetics 132: 11191130.[Abstract]
WOO, S. S., J. M. JIANG, B. S. GILL, A. H. PATERSON and R. A. WING, 1994 Construction and characterization of bacterial artificial chromosome library of Sorghum bicolor. Nucleic Acids Res. 22: 49224931.
XU, G.-W., C. W. MAGILL, K. F. SCHERTZ and G. E. HART, 1994 A RFLP linkage map of Sorghum bicolor (L) Moench. Theor. Appl. Genet. 89: 139145.
YU, H., G. H. LIANG and K. D. KOFOID, 1991 Analysis of C-banding chromosome patterns of sorghum. Crop Sci. 31: 15241527.
ZWICK, M. S., M. N. ISLAM-FARIDI, H. B. ZHANG, G. L. HODNETT, M. GOMEZ et al., 2000 Distribution and sequence analysis of the centromere-associated repetitive element CEN38 of Sorghum bicolor (Poaceae). Am. J. Bot. 87: 17571764.
This article has been cited by other articles:
![]() |
H. V. Tang, J. F. Pedersen, C. D. Chase, and D. R. Pring Fertility Restoration of the Sorghum A3 Male-Sterile Cytoplasm through a Sporophytic Mechanism Derived from Sudangrass Crop Sci., May 31, 2007; 47(3): 943 - 950. [Abstract] [Full Text] [PDF] |
||||
![]() |
J.-S. Kim, M. N. Islam-Faridi, P. E. Klein, D. M. Stelly, H. J. Price, R. R. Klein, and J. E. Mullet Comprehensive Molecular Cytogenetic Analysis of Sorghum Genome Architecture: Distribution of Euchromatin, Heterochromatin, Genes and Recombination in Comparison to Rice Genetics, December 1, 2005; 171(4): 1963 - 1976. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. E. Bowers, M. A. Arias, R. Asher, J. A. Avise, R. T. Ball, G. A. Brewer, R. W. Buss, A. H. Chen, T. M. Edwards, J. C. Estill, et al. Comparative physical mapping links conservation of microsynteny to chromosome structure and recombination in grasses PNAS, September 13, 2005; 102(37): 13206 - 13211. [Abstract] [Full Text] [PDF] |
||||
![]() |
Sorghum Genomics Planning Workshop Participants Toward Sequencing the Sorghum Genome. A U.S. National Science Foundation-Sponsored Workshop Report Plant Physiology, August 1, 2005; 138(4): 1898 - 1902. [Full Text] [PDF] |
||||
![]() |
J.-S. Kim, P. E. Klein, R. R. Klein, H. J. Price, J. E. Mullet, and D. M. Stelly Molecular Cytogenetic Maps of Sorghum Linkage Groups 2 and 8 Genetics, February 1, 2005; 169(2): 955 - 965. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |