Diversification of gene function: homologs of the floral regulatorFLO/LFYcontrol the first zygotic cell division in the mossPhyscomitrella patens

Abstract

After fertilization, the zygote undergoes dynamic changes in chromosomal and cytoplasmic organization, and begins the cell cycles that eventually lead to formation of the multicellular embryo. Specific transcription factors that initiate this cascade of events in land plants have not been identified. We have identified two FLO/LFY genes, PpLFY1 and PpLFY2, that regulate the first cell division after formation of the zygote in the moss Physcomitrella patens. The deduced amino acid sequences of the two PpLFY genes are 94.8% identical to each other and show similar expression patterns. While fertilization occurred in the PpLFY disruptants, the development of double disruptant zygotes was arrested at the single-cell stage. When the double disruptants, as the female parent, were crossed with the wild type, as the male parent, normal sporophytes were formed, supporting the notion that the PpLFY genes function after fertilization to regulate the first mitotic cell division in zygotes. The rare sporophytes that formed on the PpLFY double disruptants showed mostly normal organogenesis, but had abnormalities in the pattern of cell division, supporting a role of PpLFY genes in regulating cell division. The FLO/LFY genes in angiosperms are conserved master regulators of floral identity without any obvious effects on cell division. By contrast, our study suggests that FLO/LFY genes have functions throughout sporophyte development in the basal land plant lineages.

The evolutionary development of plant body plans

“…Physcomitrella, Ophioglossum and Ceratopteris) but are not orthologues of the ABC genes. Tanahashi et al (2005;see also Henschel et al 2002) have identified two FLORICAULA/LEAFY genes, PpLFY1 and PpLFY2, in Physcomitrella that regulate the first zygotic cell division and are thus involved in vegetative growth, whereas LFY genes among seed plants function during the vegetative to reproductive transition.…”

“…In ferns, FLO/LFY homologues are expressed predominantly in sporogenous meristematic tissues but MADS-box gene expression is not closely correlated, suggesting that these genes have not yet been subordinated to FLO/LFY regulation. In Physcomitrella, there are two FLO/LFY paralogues (PpLFY-1 and PpLFY-2), which are required for the first division of the zygote and subsequent early sporophyte development (see Henschel et al 2002;Tanahashi et al 2005). Thus, an ancient gene function has been recruited to perform new functions among embryophytes, culminating in the specification of floral organ identity.…”

Endogenous Diterpenes Derived from ent-Kaurene, a Common Gibberellin Precursor, Regulate Protonema Differentiation of the Moss Physcomitrella patens

“…The number of protonemal cells with side branches was counted in 10 protonemal cells from a protonema apical cell using protonemata grown on BCD-ATG medium under red light for 5 d. The growth rate of protonema in BCD-ATG medium (0.2% gellan gum) was analyzed by taking photographs of protonema cells at 3-min intervals. To observe the sporophytes, protonemata were inoculated using peat pellets (Jiffy-7; Jiffy Products International) in a plastic plant box (Asahi Techno Glass) as described previously (Tanahashi et al, 2005). The protonemata inoculated on the peat pellets were cultured at 25°C under 16-h-light/8-h-dark conditions for 1 month and then transferred to 15°C under 8-h-light/16-h-dark conditions.…”

Distinct regulatory role for RFL , the rice LFY homolog, in determining flowering time and plant architecture

“…Protein domains recognizable in all LFY homologs are an N-terminal proline-rich domain and a C-terminal domain; substitutions in these largely conserved DNA-binding domains are suggested to contribute to its potentially divergent functions (3). In fact, mutations in some LFY homologs show additional developmental roles (e.g., compound leaf development in pea and cell division in moss) (4,5).…”