Morphogenesis requires the coordination of
cell growth, division, and
cell differentiation. Female
gametogenesis in
flowering plants, where a single
haploid spore undergoes continuous growth and nuclear division without
cytokinesis to form an eight-nucleate
coenocytic embryo sac before cellularization, provides a good system to study the
genetic control of such processes in multicellular organisms. Here, we report the characterization of an Arabidopsis (
Arabidopsis thaliana) female gametophyte
mutant, slow walker2 (swa2), in which the progression of the
mitotic cycles and the synchrony of female gametophyte development were
impaired, causing an arrest of female gametophytes at the two-, four-, or eight-nucleate stage. Delayed pollination test showed that a portion of the
mutant ovules were able to develop into functional
embryo sacs and could be
fertilized. SWA2 encodes a nucleolar protein homologous to
yeast NUCLEOLAR COMPLEX ASSOCIATED PROTEIN1 (NOC1)/MAINTENANCE OF KILLER21 that, together with NOC2, is involved in preribosome export from the nucleus to the
cytoplasm. Similarly, SWA2 can physically interact with a putative Arabidopsis NOC2 homologue. SWA2 is expressed ubiquitously throughout the plant, at high levels in actively dividing tissues and gametophytes. Therefore, we conclude that SWA2 most likely plays a role in
ribosome biogenesis that is essential for the coordinated
mitotic progression of the female gametophyte.
