Abstract
The 18S–28S and 5S rDNA sites are useful chromosome landmarks and provide valuable evidence about genome organization and evolution. This investigation was the first attempt to study the dynamics, distribution and directionality of rDNA gains and losses, as well as to understand the contribution of site number variation in the speciation of the genus Citrullus. In this study, we employed fluorescent in situ hybridization (FISH), using the18S–28S and 5S rDNA gene loci, to evaluate the differences between the (1) cultivated type watermelon C. lanatus var. lanatus (sweet watermelon), (2) the “bitter” desert watermelon C. colocynthis (colocynth) that is indigenous to the deserts of northern Africa, the Middle East and Asia, (3) the C. lanatus var. citroides (citron) “Tsamma” or “cow watermelon” that is known as and is indigenous to southern Africa, (4) and C. rehmii that thrive in the Namibian Desert. The FISH analyses showed that the sweet watermelon and colocynth have similar rDNA configuration. The sweet watermelon and colocynth genomes contain two 18S–28S rDNA gene loci, each located on a different chromosome, and one 5S rDNA locus which is co-localized with one of the 18S–28S rDNA gene loci. On the other hand, the C. rehmii has one 18S–28S rDNA locus and one 5S rDNA locus positioned on different chromosomes, while the citron has one18S–28S rDNA and two 5S rDNA loci, each located on a different chromosome. A FISH analysis of F1 (citron × sweet watermelon) chromosome spreads revealed uniparental homeologous rDNA gene copies pertaining to the sweet watermelon versus the citron chromosomes, with the sweet watermelon chromosome containing the 18S–28S and 5S rDNA locus versus the citron homologue chromosome that has the 5S rDNA locus, but not the 18S–28S rDNA locus. Genomic in situ hybridization (GISH) analysis, using the entire citron genome as a probe to be differentially hybridized on sweet watermelon chromosome spreads, revealed that the citron genomic probes mainly hybridize to subtelomeric and pericentromeric regions of the sweet watermelon chromosomes, suggesting extensive divergence between the citron and sweet watermelon genomes. The FISH and GISH cytogenetic analysis here indicate major differences in genome organization between the cultivated watermelon type sweet watermelon and its counterpart citron that thrive in southern Africa and considered a useful germplasm source for enhancing disease and pest resistance in watermelon cultivars.
Similar content being viewed by others
References
Adams S, Leitch I, Bennett M, Chase M, Leitch A (2000) Ribosomal DNA evolution and phylogeny in Aloe (Asphodelaceae). Am J Bot 87:1578–1583
Álvarez I, Wendel JF (2003) Ribosomal ITS sequences and plant phylogenetic inference. Mol Phylogenet Evol 29:417–434
Bates DM, Robinson RW (1995) Cucumbers melon and watermelons. In: Smart J, Simmonds NW (eds) Evolution of crop plants, 2nd edn. Longman, London, pp 89–96
Berjano R, Roa F, Talavera S, Guerra M (2009) Cytotaxonomy of diploid and polyploidy Aristolochia (Aristolochiaceae) species based on the distribution of CMA/DAPI bands and 5S and 45S rDNA sites. Plant Syst Evol 280:219–227
Brown GR, Carlson JE (1997) Molecular cytogenetics of the gene encoding 18S–5.8S–26S rRNA and 5S rRNA in two species of Spruce (Picea). Theor Appl Genet 95:1–9
Burkill HM (1985) The useful plants of west tropical Africa, vol 1, 2nd edn. Royal Botanic Gardens, Kew
Dahl Jensen B, Touré FM, Hamattal MA, Touré FA, Nantoumé AD (2011) Watermelons in the Sand of Sahara: cultivation and use of indigenous landraces in the Tombouctou region of Mali. Ethnobot Res Appl 9:151–162
Dane F, Lang P (2004) Sequence variation at cpDNA regions of watermelon and related wild species: implications for the evolution of Citrullus haplotypes. Am J Bot 91:1922–1929
Dane F, Liu CJ (2007) Diversity and origin of cultivated and citron type watermelon (Citrullus lanatus). Genet Resour Crop Evol 54:1255–1265
Dane F, Lang P, Bakhtiyarova R (2004) Comparative analysis of chloroplast DNA variability in wild and cultivated Citrullus species. Theor Appl Genet 108:958–966
Dane F, Liu J, Zhang C (2007) Phylogeography of the bitter apple, Citrullus colocynthis. Genet Resour Crop Evol 54:327–336
Dover G (1986) Concerted evolution, molecular drive and natural selection. Curr Biol 4:1165–1166
Fransz PF, Armstrong S, Alonso-Blanco C, Fischer TC, Torres-Ruiz RA, Jones GH (1998) Cytogenetics for the model species Arabidopsis thaliana. Plant J 13:867–876
Fukushima K, Nagano K, Hoshi Y (2008) Somatic chromosome differentiation in three species of the Byblis liniflora complex (Byblidaceae). Chromosom Bot 3:95–99
Fursa T (1972) K sistematike roda Citrullus Schrad. Bot Zhurn 57:31–41
Gu ZJ, Xiao H (2003) Physical mapping of the 18S–26S rDNA by fluorescent in situ hybridization (FISH) in Camellia reticulata polyploidy complex (Theaceae). Plant Sci 164:279–285
Hanson RE, Islam-Faridi MN, Percival EA, Crane CF, McKnight TD, Stelly DM, Price HJ (1996) The distribution of 5S and 18S–28S rDNA loci in tetraploid cotton (Gossypium hirsutum L.) and its putative diploid ancestors. Chromosoma 105:55–61
Heslop-Harrison JS (1991) The molecular cytogenetics of plants. J Plant Sci 100:15–21
Hizume M, Ishida MF, Murata M (1992) Multiple locations of ribosomal RNA genes in chromosomes of pines, P. densiflora and P. thunberghii. Jpn J Genet 67:389–396
Islam-Faridi MN, Childs KL, Klein PE, Hodnett G, Menz MA, Klein RR, Rooney WL, Mullet JE, Stelly DM, Price HJ (2002) A molecular cytogenetic map of sorghum chromosome1: fluorescence in situ hybridization analysis with mapped bacterial artificial chromosomes. Genetics 161:345–353
Islam-Faridi MN, Nelson CD, Kubisiak TL (2007) Reference karyotype and cyto molecular map for loblolly pine (Pinus taeda L.). Genome 50:241–251
Jarret RL, Newman M (2000) Phylogenetic relationships among species of Citrullus and the placement of C. rehmii De Winter as determined by internal transcribed spacer (ITS) sequence heterogeneity. Genet Resour Crop Evol 47:215–222
Jarret RL, Merrick LC, Holms T, Evans J, Aradhya MK (1997) Simple sequence repeats in watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai]. Genome 40:433–441
Jeffrey C (2001) Cucurbitaceae (Citrullus). In: Hanelt P, Institute of Plant Genet and Crop Plant Research (eds) Mansfeld’s encyclopedia of agricultural and horticultural crops. Springer, New York, pp 1510–1557
Jewell DC, Islam-Faridi MN (1994) A technique for somatic chromosome preparation and C-banding of maize. In: Freeling M, Walbot V (eds) The maize handbook. Springer-Verlag, New York, pp 484–493
Laghetti G, Hammer K (2007) The Corsican citron melon (Citrullus lanatus (Thunb.) Matsum. et Nakai subsp. lanatus var. citroides (Bailey) Mansf. ex Greb.), a traditional and neglected crop. Genet Resour Crop Evol 54:913–916
Leitch IJ, Heslop-Harrison JS (1992) Physical mapping of the 18S–5.8S–25S rRNA genes in barley by in situ hybridization. Genome 35:1013–1018
Levi A, Thomas CE, Keinath AP, Wehner TC (2001) Genetic diversity among watermelon (Citrullus lanatus and Citrullus colocynthis) accessions. Genet Resour Crop Evol 48:559–566
Levi A, Thomas CE, Joobeur T, Zhang X, Davis A (2002) A genetic linkage map for watermelon derived from a testcross population: (Citrullus lanatus var. citroides × C. lanatus var. lanatus) × C. colocynthis. Theor Appl Genet 105:555–563
Levi A, Thomas CE, Trebitsh T, Salman A, King J, Karalius J, Newman M, Reddy UK, Xu Y, Zhang X (2006) An extended linkage map for watermelon based on SRAP, AFLP, SSR, ISSR and RAPD markers. J Am Soc Hortic Sci 131:393–402
Linares C, Gonzalez J, Ferrer E, Fominaya A (1996) The use of double fluorescence in situ hybridization to physically map the positions of 5S rDNA genes in relation to the chromosomal location of 18S–5.8S–26S rDNA and a C genome specific DNA sequence in the genus Avena. Genome 39:535–542
Martínez J, Vargas P, Luceño M, Cuadrado Á (2010) Evolution of Iris subgenus Xiphium based on chromosome numbers, FISH of nrDNA (5S, 45S) and trnL- trnF sequence analysis. Plant Syst Evol 289:223–235
Meeuse ADJ (1962) The Cucurbitaceae of southern Africa. Bothalia 8:111
Mujaju C, Sehic J, Werlemark G, Garkava-Gustavsson L, Faith M, Nybom H (2010) Genetic diversity in watermelon (Citrullus lanatus) landraces from Zimbabwe revealed by RAPD and SSR markers. Hereditas 147:142–153
Murata M, Heslop-Harrison JS, Motoyoshi F (1997) Physical mapping of the 5S ribosomal RNA genes in Arabidopsis thaliana by multi-color FISH with cosmid clones. Plant J 12:31–37
Navot N, Zamir D (1987) Isozyme and seed protein phylogeny of the genus Citrullus (Cucurbitaceae). Plant Syst Evol 156:61–68
Nimmakayala P, Tomason YR, Jeong J, Ponniah SK, Karunathilake A, Levi A, Perumal R, Reddy UK (2010) Genetic reticulation and interrelationships among Citrullus species as revealed by joint analysis of shared AFLPs and species-specific SSR alleles. Plant Genet Resour 8:16–25
Ohta T (1984) Some models of gene conversion for treating the evolution of multigene families. Genetics 106:517–528
Pedrosa-Harand CC, de Almeida S, Mosiolek MM, Blair WD, Schweizer W, Guerra M (2006) Extensive ribosomal DNA amplification during Andean common bean (Phaseolus vulgaris L.) evolution. Theor Appl Genet 112:924–933
Robinson RW, Decker-Walters DS (1997) Cucurbits. CAB international, Wallingford
Rubatsky VE (2001) Origin, distribution and uses. In: Maynard D (ed) Watermelons, characteristics, production, and marketing. ASHS Press, Alexandria
Schmidt T, Schwarzacher T, Heslop-Harrison JS (1994) Physical mapping of rRNA genes by fluorescent in situ hybridization and structural analysis of 5S rRNA genes and intergenic spacer sequences in sugar-beet (Beta vulgaris L.). Theor Appl Genet 88:629–636
Whitaker TW, Bemis WB (1976) Cucurbits. In: Simmonds NW (ed) Evolution of crop plants. Longman, London, pp 64–69
Whitaker TW, Davis GN (1962) The Cucurbits: botany, cultivation and utilization. Interscience Publishers, New York
Zamir D, Navot N, Rudich J (1984) Enzyme polymorphism in Citrullus lanatus and C. colocynthis in Israel and Sinai. Plant Syst Evol 146:163–170
Zimmer EA, Jupe ER, Walbot V (1988) Ribosomal gene structure, variation and inheritance in maize and its ancestors. Genetics 120:1125–1136
Acknowledgments
The authors are grateful to Dr. Jarret, Plant Genetic Resources Conservation Unit, USDA-ARS, Griffin, GA, 30223 for providing the seeds of germplasm accessions. Funding support is provided by NSF-EPSCOR#1003907, Gus R. Douglass Institute and USDA-NIFA Research (2010-02247).
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Reddy, U.K., Aryal, N., Islam-Faridi, N. et al. Cytomolecular characterization of rDNA distribution in various Citrullus species using fluorescent in situ hybridization. Genet Resour Crop Evol 60, 2091–2100 (2013). https://doi.org/10.1007/s10722-013-9976-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10722-013-9976-1