Evolution of Internal Transcribed Spacer Region of Nuclear Ribosomal DNA in Allopolyploids of Aegilops

Abstract

Abstract:

Hybridization with subsequent polyploidy is a prominent process in evolution of higher

plants, but few data address the evolution of homeologous sequences after polyploidy. The internal

transcribed spacer (ITS) of nuclear ribosomal DNA (nrDNA) from eleven allopolyploid species in

Aegilops was investigated by PCR amplification and direct sequencing. The sequences obtained were

used to study the evolution of ITS region in allopolyploid species. The length of ITS region varied

from 599 to 606 bp and the number of variable sites was 93, i.e. 51 and 42 for ITS1 and ITS2 re-

spectively. Some polymorphic sites were observed in polyploid species, and this indicated that the

ancestral sequences had not been homogenized completely by concerted evolution. Distance matrix

analysis of diploid and polyploid species by neighbor-joining method, using Triticum monococcum as

outgroup, resulted in well-resolved neighbor-joining tree indicating that the ITS regions of UUMM

and UUSS genome ( sect. Vertebrata) were homogenizing toward those of UU ancestal genome. This

result is in agreement with the results of ctyogenetics of Aegilops. On the other hand, the neighbor-

joining tree including the D-genome group species (sect. Cylindropyrum and sect. Polyeides ) com-

prised three clades (CC-DDCC, UU-DDMM-DDMMSS-DDMMUU and MM-DDMvMv), which sug-

gested that concerted evolution was homogenizing the ITS region of the polyploid derivatives to either

of their ancestors.

Key words: Aegilops, Allopolyploid, ITS sequence, Evolution

WANG Chao, WANG Jian-Bo, SHI Su-Hua, ZHONG Yang. Evolution of Internal Transcribed Spacer Region of Nuclear Ribosomal DNA in Allopolyploids of Aegilops[J]. , 2000, 38(3): 211-217.

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Evolution of Internal Transcribed Spacer Region of Nuclear Ribosomal DNA in Allopolyploids of Aegilops

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