Gene organization of the Y chromosome of the liverwort, Marchantia polymorpha

Abstract

In the liverwort M. polymorpha, a specific Y chromosome is present in the male, and an X chromosome is found only in the female plants. This X/Y exclusiveness strongly suggests the presence of sex-determining factors on the sex chromosomes. The liverwort Y chromosome has an approximately 4-Mb region (YR1) which has accumulated its own repetitive sequences. The other part of the Y chromosome is designated as YR2 which contains genes unique to the Y chromosome. We have obtained draft sequences of 25 representative PAC clones and a 470-kb contig in YR1. Forty-five PAC clones were selected from two contigs (5.94 Mb) in YR2 and sequenced. Most genes identified in YR1 are present in multicopy. Contrastingly genes present in YR2 are mostly single-copied. Gene structure evolution of the Y chromosome and its genes in M. polymorpha as well as difference in gene structure between the X and Y chromosomes are discussed.