title: A small, novel protein highly conserved in plants and animals promotes the polarized growth and division of maize leaf epidermal cells.
abstract: Plant cell shapes are defined by their surrounding walls, but microtubules and F-actin both play critical roles in cell morphogenesis by guiding the deposition of wall materials in expanding cells. Leaf epidermal cells have lobed shapes, which are thought to arise through a microtubule-dependent pattern of locally polarized growth. We have isolated a recessive mutation, brk1, which blocks the formation of epidermal cell lobes in the maize leaf. Mutant epidermal cells expand to the same extent as wild-type cells but fail to establish polar growth sites from which lobes arise. In expanding brk1 epidermal cells, microtubule organization differs little from that in wild-type, but localized enrichments of cortical F-actin seen at the tips of emerging lobes in wild-type cells fail to form. These observations suggest a critical role for F-actin in lobe formation and together with additional effects of brk1 on the morphogenesis of stomata and hairs suggest that Brk1 promotes multiple, actin-dependent cell polarization events in the developing leaf epidermis. The Brk1 gene encodes a novel, 8 kD protein that is highly conserved in plants and animals, suggesting that BRK1-related proteins may function in actin-dependent aspects of cell polarization in a wide spectrum of eukaryotic organisms.
authors.affiliation: Section of Cell and Developmental Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA.
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Frank
authors.forename: Laurie G
authors.initials: LG
authors.lastname: Smith
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D016764:Cell Polarity; D017124:Conserved Sequence; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D019441:Plant Epidermis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000166:cytology / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D010940:Plant Proteins; D012333:RNA, Messenger