Chromosomal Locations of 5S and 45S rDNA in Gossypium Genus and Its Phylogenetic Implications Revealed by FISH

Yimei Gan,Fang Liu,Kunbo Wang,Qiong Wu,Yuhong Wang,Xiangdi Zhang,Dan Chen,Chunying Wang,Qin Qin,Shaohui Li,Baohong Zhang

doi:10.1371/journal.pone.0068207

Abstract

We investigated the locations of 5S and 45S rDNA in Gossypium diploid A, B, D, E, F, G genomes and tetraploid genome (AD) using multi-probe fluorescent in situ hybridization (FISH) for evolution analysis in Gossypium genus. The rDNA numbers and sizes, and synteny relationships between 5S and 45S were revealed using 5S and 45S as double-probe for all species, and the rDNA-bearing chromosomes were identified for A, D and AD genomes with one more probe that is single-chromosome-specific BAC clone from G. hirsutum (A1D1). Two to four 45S and one 5S loci were found in diploid-species except two 5S loci in G . incanum (E4), the same as that in tetraploid species. The 45S on the 7th and 9th chromosomes and the 5S on the 9th chromosomes seemed to be conserved in A, D and AD genomes. In the species of B, E, F and G genomes, the rDNA numbers, sizes, and synteny relationships were first reported in this paper. The rDNA pattern agrees with previously reported phylogenetic history with some disagreements. Combined with the whole-genome sequencing data from G . raimondii (D5) and the conserved cotton karyotype, it is suggested that the expansion, decrease and transposition of rDNA other than chromosome rearrangements might occur during the Gossypium evolution.

Highlights

Cotton (Gossypium) is an important economic fiber crop
Three 45S Ribosomal DNA (rDNA) loci and two 5S rDNA loci were detected in all three tetraploid species (Figure 1 a, b, c)
The number of 45S rDNA loci was detected three, two, four and three in D5, D6, D9, D11, respectively, while only one 5S rDNA locus was observed in the four D genome species (Figure 1d– 1g)

Summary

Introduction

Cotton (Gossypium) is an important economic fiber crop. The genus of Gossypium comprises about 50 species throughout tropical and subtropical regions of the world, including five tetraploid (2n=4x=52) species and about 45 diploid (2n=2x=26) species. The taxonomic and evolution study on Gossypium genus has been an important subject of investigation due to its economic significance. In the late 1800’s or early 1900’s, the taxonomy was mainly based on morphological characteristics and geographical distributions, it has been confusion due to un-consensus characteristics used by different taxonomists. The evolutionary history of Gossypium genus was reconstruct based on geography, morphology, cytogenetics and molecular data. Due to the continuous recombination and exchange, great differences existed between existing cotton species and their ancestors in terms of physiological feature, agronomic trait and morphology. More interpretation about the phylogenetic and interspecific evolution in Gossypium genus is quite necessarily to be clarified

Methods

Results

Conclusion