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Comparative Study
. 2016 Apr 18:16:85.
doi: 10.1186/s12862-016-0656-6.

Cytogenetic relationships among Citrullus species in comparison with some genera of the tribe Benincaseae (Cucurbitaceae) as inferred from rDNA distribution patterns

Kun-Peng Li  1 , Yun-Xiang Wu  1 , Hong Zhao  2 , Yan Wang  1 , Xing-Ming Lü  1 , Ji-Ming Wang  3 , Yong Xu  2 , Zong-Yun Li  4 , Yong-Hua Han  5
Affiliations
Comparative Study

Cytogenetic relationships among Citrullus species in comparison with some genera of the tribe Benincaseae (Cucurbitaceae) as inferred from rDNA distribution patterns

Kun-Peng Li et al. BMC Evol Biol. .

Abstract

Background: Comparative mapping of 5S and 45S rDNA by fluorescent in situ hybridization (FISH) technique is an excellent tool to determine cytogenetic relationships among closely related species.

Results: In this study, the number and position of 5S and 45S rDNA loci in all Citrullus species and subspecies were determined. The cultivated watermelon (C. lanatus subsp. vulgaris), C. lanatus subsp. mucosospermus, C. colocynthis and C. naudinianus (or Acanthosicyos naudinianus) had two 45S rDNA loci and one 5S rDNA locus which was located syntenic to one of the 45S rDNA loci. C. ecirrhosus and C. lanatus subsp. lanatus had one 45S rDNA locus and two 5S rDNA loci, each located on a different chromosome. C. rehmii had one 5S and one 45S rDNA locus positioned on different chromosomes. The distribution of 5S and 45S rDNA in several species belonging to other genera in Benincaseae tribe was also investigated. The distribution pattern of rDNAs showed a great difference among these species.

Conclusions: The present study confirmed evolutionary closeness among cultivated watermelon (C. lanatus subsp. vulgaris), C. lanatus subsp. mucosospermus and C. colocynthis. Our result also supported that C. lanatus subsp. lanatus was not a wild form of the cultivated watermelon instead was a separate crop species. In addition, present cytogenetic analysis suggested that A. naudinianus was more closely related to Cucumis than to Citrullus or Acanthosicyos, but with a unique position and may be a link bridge between the Citrullus and the Cucumis.

Keywords: Citrullus species; Cytogenetic relationship; Fluorescence in situ hybridization; Oligonucleotides probes; rDNA.

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Figures

Fig. 1
Fig. 1
FISH of watermelon oligos probes, 5S and 45S rDNA in Citrullus species and Acanthosicyos naudinianus. a1-g1 FISH oligos probes Library 1 (green) and Library 2 (red) on metaphase chromosomes of C. lanatus subsp. vulgaris (a1), C. lanatus subsp. mucosospermus (b1), C. colocynthis (c1), C. lanatus subsp. lanatus (d1), C. ecirrhosus (e1), C. rehmii (f1) and A. naudinianus (g1), respectively. a2-g2 The same cells in A1-G1 were reprobed with 5S rDNA (red) and 45S rDNA (green) probes. a3-g3 The chromosomes with the signals of the oligos probes Library 1 (green) and Library 2 (red) in a1-g1. a4-g4 The chromosomes with the signals of 5S rDNA (red) and 45S rDNA (green) probes in a2-g2. Bars, 5 mm
Fig. 2
Fig. 2
FISH of 5S rDNA (red) and 45S rDNA (green) probes in eight species from other genera in Benincaseae tribe. a Lagenaria siceraria. b Zehneria mariothii. c Melothria pendula. d Cucumis metuliferus. e Benincasa fistulosa. f Coccinia sessilifolia. g Diplocyclos palmatus. h Cucumis sativus. Bars, 5 mm
Fig. 3
Fig. 3
FISH of melon oligos probes, 5S and 45S rDNA in Cucumis metuliferus and Acanthosicyos naudinianus. a1-b1 FISH oligos probes Library 1 (green) and Library 2 (red) on metaphase chromosomes of C. metuliferus (a1) and A. naudinianus (b1). a2-b2 The same cells in a1-b1 were reprobed with 5S rDNA (red) and 45S rDNA (green) probes. a3-b3 The chromosomes with the signals of the oligos probes Library 1 (green) and Library 2 (red) in a1-b1. a4-b4 The chromosomes with the signals of 5S rDNA (red) and 45S rDNA (green) probes in a2-b2. Bars, 5 mm
Fig. 4
Fig. 4
A scheme showing phylogenetic relationships among the Citrullus species
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