Two types of plastid ftsZ genes in the liverwort Marchantia polymorpha

Two types of ftsZ genes (MpftsZ1 and MpftsZ2) were isolated from the liverwort Marchantia polymorpha by degenerate reverse transcription PCR. The MpFtsZ1 and MpFtsZ2 proteins are predicted to localize in chloroplasts. Genomic Southern analysis suggested that each ftsZ gene is a single-copy nuclear gene. Northern analysis confirmed that both genes are active. A phylogenetic tree constructed with the deduced MpFtsZ amino acid sequences suggests that MpFtsZ1 and MpFtsZ2 can be classified into the plant chloroplastic FtsZ1 and FtsZ2 families, respectively. This result suggests that two ftsZ families exist universally in land plants. The determination of the intron structures of both MpftsZ genes supported this hypothesis. The transformation of a sense MpftsZ2 overexpression construct into M. polymorpha produced a large chloroplast phenotype in a transgenic plant. The mean number of chloroplasts was 38.2 (standard deviation, 21.4; n = 200) in epidermal cells of wild-type plants, whereas the mean number of chloroplasts was 7.4 (standard deviation, 4.4; n = 200) in the transgenic plant. Southern analysis showed that the cauliflower mosaic virus 35S promoter-MpftsZ2 construct was inserted in at least three positions. Northern analysis suggested that the high accumulation of MpftsZ2 mRNA blocked plastid division. Determination of the chlorophyll content and the chlorophyll fluorescence parameters suggested that the macrochloroplasts function like chloroplasts in wild-type plants under normal light conditions. However, the transgenic plant grew more slowly than did wild-type plants.