The Y chromosome in the liverwort Marchantia polymorpha has accumulated unique repeat sequences harboring a male-specific gene

Abstract

The haploid liverwort Marchantia polymorpha has heteromorphic sex chromosomes, an X chromosome in the female and a Y chromosome in the male. We here report on the repetitive structure of the liverwort Y chromosome through the analysis of male-specific P1-derived artificial chromosome (PAC) clones, pMM4G7 and pMM23-130F12. Several chromosome-specific sequence elements of Ϸ70 to 400 nt are combined into larger arrangements, which in turn are assembled into extensive Y chromosome-specific stretches. These repeat sequences contribute 2-3 Mb to the Y chromosome based on the observations of three different approaches: fluorescence in situ hybridization, dot blot hybridization, and the frequency of clones containing the repeat sequences in the genomic library. A novel Y chromosome-specific gene family was found embedded among these repeat sequences. This gene family encodes a putative protein with a RING finger motif and is expressed specifically in male sexual organs. To our knowledge, there have been no other reports for an active Y chromosome-specific gene in plants. The chromosome-specific repeat sequences possibly contribute to determining the identity of the Y chromosome in M. polymorpha as well as to maintaining genes required for male functions, as in mammals such as human.dioecism ͉ sex chromosome ͉ FISH ͉ RING finger motif ͉ convergent evolution

The role of repetitive DNA in structure and evolution of sex chromosomes in plants

“…The Y chromosome of liverwort has specific repeat sequences that contain multiplicated genes. These data suggest that the Y chromosome-amplified protein-coding genes evolved in concert with specific repeat sequences (Okada et al, 2001;Ishizaki et al, 2002).…”

Gene organization of the liverwort Y chromosome reveals distinct sex chromosome evolution in a haploid system

“…The YR1 domain consists of unique small repeat sequences of only several hundred nucleotides, which are assembled in various stoichiometries to form different arrangements of the 2.4-kb BamHI repeat family. Structures and sequences of these elements have been analyzed (23). When DNA of clone pMM23-104E4 (contig A of YR2), which is one of the first clones isolated from YR2 (25), and a fragment of the 2.4-kb BamHI repeat were simultaneously applied to prometaphase chromosomes of male plants in FISH experiments, the signal of the 2.4-kb BamHI repeat (yellowish green signal in Fig.…”

“…Sequencing of PAC clones was performed by a shotgun method as described (23). Some of the shotgun reads were produced by Shimadzu, Kyoto, Japan.…”

“…PCR for determining sex specificity of putative genes and linkage analysis was performed basically as described (23). Template genomic DNAs were isolated as described (29), and 10 ng each was used per assay.…”

“…Preparation of chromosome spreads from young thalli of M. polymorpha and FISH was performed as described (23,26,38). For ordering contig A and contig B (Fig.…”