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Letters to Nature

Nature 429, 776-780 (17 June 2004) | doi:10.1038/nature02637; Received 4 March 2004; Accepted 10 May 2004

Plant retinoblastoma homologues control nuclear proliferation in the female gametophyte

Chantal Ebel1, Luisa Mariconti1 & Wilhelm Gruissem1

  1. Institute of Plant Sciences, Swiss Federal Institute of Technology, ETH Zürich, Universitätstrasse 2, CH-8092 Zürich, Switzerland

Correspondence to: Wilhelm Gruissem1 Email: wilhelm.gruissem@ipw.biol.ethz.ch

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Haploid spores of plants divide mitotically to form multicellular gametophytes. The female spore (megaspore) of most flowering plants develops by means of a well-defined programme into the mature megagametophyte consisting of the egg apparatus and a central cell1, 2. We investigated the role of the Arabidopsis retinoblastoma3, 4 protein homologue and its function as a negative regulator of cell proliferation during megagametophyte development. Here we show that three mutant alleles of the gene for the Arabidopsis retinoblastoma-related protein, RBR1 (ref. 4), are gametophytic lethal. In heterozygous plants 50% of the ovules are aborted when the mutant allele is maternally inherited. The mature unfertilized mutant megagametophyte fails to arrest mitosis and undergoes excessive nuclear proliferation in the embryo sac. Supernumerary nuclei are present at the micropylar end of the megagametophyte, which develops into the egg apparatus and central cell. The central cell nucleus, which gives rise to the endosperm after fertilization, initiates autonomous endosperm development reminiscent of fertilization-independent seed (fis) mutants5. Thus, RBR1 has a novel and previously unrecognized function in cell cycle control during gametogenesis and in the repression of autonomous endosperm development.