The Arabidopsis KLUNKER gene controls cell shape changes and encodes the AtSRA1 homolog

Abstract

The analysis of a group of seven trichome mutants in Arabidopsis, which all show distorted trichomes along with severe actin defects has revealed insight into the role of the actin cytoskeleton in cell shape control. Four of the corresponding genes encode components of a protein complex, the ARP2/3 complex that stimulates the production of 'fine actin' at active growth sites. In this study, we show that another member of the distorted group, KLUNKER (KLK), encodes the AtSRA1 homolog of Arabidopsis and that klk mutants show a similar range of cell shape defects to those of arp2/3 mutants. In animals, SRA1 regulates the activity of the ARP2/3-regulating WAVE-HSPC300 complex in a Rho-dependent manner. Our findings provide evidence that a Rho/ARP2/3 regulation pathway exists in plants.

The Endoplasmic Reticulum Is a Reservoir for WAVE/SCAR Regulatory Complex Signaling in the Arabidopsis Leaf

“…Interestingly, the ER localization of NAP1 in pavement cells is not affected either in spk1, in which W/SRC is inactive (Basu et al, 2008), or in sra1 cells, in which W/SRC is incompletely assembled and has little or no activity Brembu et al, 2004;Saedler et al, 2004). These genetic data clearly demonstrate that inactive NAP1 associates with ER membranes and that its binding partner, SRA1, is not necessary for either the stability of the NAP1 protein or its association with the ER.…”

The role ofArabidopsis SCARgenes in ARP2-ARP3-dependent cell morphogenesis

“…Four plant homologues of the five components of the SCAR regulatory complex have now been associated with phenotypes that either resemble arp2-arp3 complex mutant alleles (Basu et al, 2004;Brembu et al, 2004;El-Assal et al, 2004a;Saedler et al, 2004b;Zimmermann et al, 2004) or are correlated with disruption of the Factin cytoskeleton (Frank and Smith, 2002).…”

“…Epidermal cell lobe phenotypes associated with ARP2-ARP3 complex mutations and mutations of ARP2-ARP3 complex regulators suggest that ARP2-ARP3 complex activity affects the development of plant epidermal lobes by influencing either the magnitude of lobe expansion (Brembu et al, 2004;Frank et al, 2003;Li et al, 2003;Mathur et al, 2003a;Mathur et al, 2003b;Saedler et al, 2004a;Saedler et al, 2004b) or cell-cell adherence following lobe intercalation (Basu et al, 2004;El-Assal et al, 2004b;Le et al, 2003). Surprisingly, the atscar2 mutants showed well-developed epidermal lobes.…”

“…The corresponding mutants show an aberrant actin phenotype and affect the same cell types as the arp2-arp3 complex mutants except for the root hairs, indicating that they regulate most aspects of the ARP2-ARP3 complex function (Basu et al, 2004;Brembu et al, 2004;Deeks et al, 2004;El-Assal et al, 2004a;Saedler et al, 2004b;Zimmermann et al, 2004). Recently it was shown that HSPC300 is conserved in plants (as BRICK1, BRK1), and the analysis of the corresponding maize and Arabidopsis mutants also revealed a distorted phenotype and an involvement in the regulation of actin (Djakovic et al, 2006;Frank and Smith, 2002;Le et al, 2006).…”

Differential Growth in Periclinal and Anticlinal Walls during Lobe Formation in Arabidopsis Cotyledon Pavement Cells

“…The importance of actin filaments and actin binding proteins in lobe formation is clear because the pavement cells in a number of Arabidopsis mutants of a signaling cascade upstream of actin filaments have either smaller or no recognizable lobes. Proteins in this cascade include Rho of plants (ROP) and ROP interactive crib motif protein (RIC) (Fu et al, 2002(Fu et al, , 2005, ROP guanine nucleotide exchange factor (ROP-GEF) (Qiu et al, 2002;Basu et al, 2008), the actin related 2/3 (ARP2/3) complex (Le et al, 2003;Li et al, 2003;Mathur et al, 2003aMathur et al, , 2003bSaedler et al, 2004), and the suppressor of cyclic AMP receptor (SCAR) complex (Basu et al, 2004(Basu et al, , 2005Brembu et al, 2004;Zhang et al, 2005Zhang et al, , 2008Le et al, 2006). Plant cell expansion is perpendicular to the net orientation of cellulose microfibrils in the cell wall (Baskin et al, 1999;Geitmann and Ortega, 2009).…”