First published online October 29, 2004; 10.1104/pp.104.053173
Plant Physiology 136:3616-3627 (2004)
© 2004 American Society of Plant Biologists
CELL BIOLOGY AND SIGNAL TRANSDUCTION
Arabidopsis NAP and PIR Regulate Actin-Based Cell Morphogenesis and Multiple Developmental Processes1
Yunhai Li2,
Karim Sorefan2,
Georg Hemmann2 and
Michael W. Bevan*
Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom
The actin cytoskeleton mediates cellular processes through the dynamic regulation of the time, location, and extent of actin polymerization. Actin polymerization is controlled by several types of evolutionarily conserved proteins, including those comprising the ARP2/3 complex. In animal cells ARP2/3 activity is regulated by WAVE complexes that contain WAVE/SCAR proteins, PIR121, Nap125, and other proteins. The activity of the WAVE complex is regulated by Rho-GTPase-mediated signaling that leads to ARP2/3 activation by WAVE/SCAR proteins. We describe in this report Arabidopsis (Arabidopsis thaliana) genes encoding Nap and PIR proteins. Light-grown Atnap-1 and Atpir-1 mutant plants displayed altered leaf, inflorescence, silique, and seed set phenotypes. Dark-grown Atnap-1 and Atpir-1 seedlings also exhibited longer roots, enhanced skotomorphogenesis and Glc responses, and shorter thicker hypocotyls than those of wild type, showing that AtNAP and AtPIR participate in a variety of growth and developmental processes. Mutations in AtNAP and AtPIR caused cell morphology defects in cotyledon pavement cells and trichomes seen in mutants in ARP2/3 subunits and in plants expressing constitutively active Rop2 GTPase. The patterns and levels of actin polymerization observed in Atnap-1 and Atpir-1 mutant trichome cells and epidermal pavement cell morphology is consistent with Arabidopsis NAP and PIR proteins forming a WAVE complex that activates ARP2/3 activity. The multiple growth and developmental phenotypes of Atnap and Atpir mutants reveals these proteins are also required for a wider variety of cellular functions in addition to regulating trichome cell growth.
1 This work was supported by the Biotechnology and Biological Sciences Research Council (grant no. 208/EGM16126), by Syngenta (grant no. PMC19), and by the John Innes Centre Core Strategic Grant (to M.W.B.).
2 These authors contributed equally to the paper.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.053173.
* Corresponding author; e-mail michael.bevan{at}bbsrc.ac.uk; fax 01603–450025.
Received September 9, 2004;
returned for revision September 30, 2004;
accepted September 30, 2004.
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