Actin-Related Protein2/3 Complex Component ARPC1 Is Required for Proper Cell Morphogenesis and Polarized Cell Growth in Physcomitrella patensW

• Published in: The Plant cell Vol. 17; no. 8; pp. 2327 - 2339
• Main Authors: Harries, Phillip A., Pan, Aihong, Quatrano, Ralph S.
• Format: Journal Article
• Language: English
• Published: American Society of Plant Biologists 01-08-2005
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.105.033266

The actin-related protein2/3 (Arp2/3) complex functions as a regulator of actin filament dynamics in a wide array of eukaryotic cells. Here, we focus on the role of the Arp2/3 complex subunit ARPC1 in elongating tip cells of protonemal filaments of the moss
Physcomitrella patens
. Using RNA interference (RNAi) to generate loss-of-function mutants, we show dramatic defects in cell morphology manifested as short, irregularly shaped cells with abnormal division patterns. The
arpc1
RNAi plants lack the rapidly elongating caulonemal cell type found in wild-type protonemal tissue. The absence of this cell type prevents normal bud formation even in response to cytokinin treatment and results in filamentous colonies lacking leafy gametophores. In addition,
arpc1
protoplasts show an increased sensitivity to osmotic shock and are defective in their ability to properly establish a polarized outgrowth during regeneration from a single cell. This failure of
arpc1
protoplasts to undergo proper tip growth is rescued by ARPC1 overexpression and is phenocopied in wild-type protoplasts treated with Latrunculin B, a potent inhibitor of actin polymerization. We show in moss that ARPC1, and by inference the Arp2/3 complex, plays a critical role in controlling polarized growth and cell division patterning through its regulation of actin dynamics at the cell apex.