Abstract
Zingeria (Poaceae) is a small genus that includes Z. biebersteiniana, a diploid species with the lowest chromosome number known in plants (2n = 4) as well as hexaploid Z. kochii and tetraploid Z. pisidica, and/or Z. trichopoda species. The relationship between these species and the other low-chromosomes species Colpodium versicolor are unclear. To explore the intragenomic polymorphism and genome composition of these species we examined the sequences of the internal transcribed spacer 1 of the 35S rRNA gene via NGS approach. Our study revealed six groups of ribotypes in Zingeria species. Their distribution confirmed the allopolyploid nature of Z. kochii, whose probable ancestors were Colpodium versicolor and Z. pisidica. Z. pisidica has 98% of rDNA characteristic only for this species, and about 0.3% of rDNA related to that of Z. biebersteiniana. We assume that hexaploid Z. kochii is either an old allopolyploid or a homodiploid that has lost most of the rRNA genes obtained from Z. biebersteiniana. In Z. trichopoda about 81% of rDNA is related to rDNA of Z. biebersteiniana and 19% of rDNA is derived from Poa diaphora sensu lato. The composition of the ribotypes of the two plants determined by a taxonomy specialist as Z. pisidica and Z. trichopoda is very different. Two singleton species are proposed on this base with ribotypes as discriminative characters. So, in all four studied Zingeria species, even if the morphological difference among the studied species was modest, the genomic constitution was significantly different, which suggests that these are allopolyploids that obtained genomes from different ancestors.
Highlights
Interspecific hybridization, often accompanied by the formation of allopolyploid genomes, allows plants to bypass the prohibitions on sympatric speciation known from the synthetic theory of evolution [1,2]
Six ribotypes were shared between Zingeria and Colpodium species and two ribotypes were found in studied Catabrosella species
Ribotype A (Figures 1 and 2) included intragenomic variants of ITS1 from Catabrosella araratica (Lipsky) Tzvelev. This ribotype included all sequences of Catabrosella araratica from GenBank and formed a separated network, not connected with ribotypes of Zingeria and Colpodium (Figure 1)
Summary
Interspecific hybridization, often accompanied by the formation of allopolyploid genomes, allows plants to bypass the prohibitions on sympatric speciation known from the synthetic theory of evolution [1,2]. Various genetic processes, such as the loss of all or part of the chromosomes of one of the parents, the expansion of transposons, translocations and transpositions, and the loss of a part of the genes of one or both parental genomes, take place in complicated allopolyploid genomes [3,4]. The diploid species Zingeria biebersteiniana (Claus) P.A. Smirn.
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