Identification of repetitive sequences containing motifs of retrotransposons in the ectomycorrhizal basidiomycete Tricholoma matsutake

Abstract

An ectomycorrhizal basidiomycete, Tricholoma matsutake, produces fruiting bodies known as matsutake mushrooms in Pinus sp. forests. Matsutake mushrooms are a commercially valuable edible fungi. By using designed oligonucleotides as primers and genomic DNA of T. matsutake strain Y1 as a template, 967 and 1375 bp nucleotides were amplified by the polymerase chain reaction (PCR). The fragments consist of repetitive sequences and are predicted to encode peptides highly similar to those of reverse transcriptase, RNase H and integrase of retrotransposons. Internal fragments of 967 bp and 1375 bp DNA hybridized to genomic digests of T. matsutake isolated from various locations, and a strain of Tricholoma magnivelare. No hybridization was detected in 9 other Tricholoma species and one species each of 3 other genera of basidiomycetes that form an ectomycorrhizal symbiosis with the Pinus sp. tested. Hybridization signals generated by a probe of the 967 bp fragment were much stronger than those of the 1375 bp fragment. Restriction fragment length polymorphism revealed that DNA segments containing the 967 bp fragments are highly conserved in strains of T. matsutake and T. magnivelare whereas those containing the 1375 bp fragments are markedly diversified between these species. PCR with primers used for cloning of these fragments and those designed based on internal complementary inverted repeats showed both conservation and differentiation of the repetitive sequences containing motifs of retrotransposons in T. matsutake and the closely related fungi T. magnivelare.

Key Words:

• integrase
• molecular evolution
• Pinus densiflora
• reverse transcriptase
• RNase H
• Tricholoma magnivelare