ArabidopsisCAP1 – a key regulator of actin organisation and development

Abstract

Maintenance of F-actin turnover is essential for plant cell morphogenesis. Actin-binding protein mutants reveal that plants place emphasis on particular aspects of actin biochemistry distinct from animals and fungi. Here we show that mutants in CAP1, an A. thaliana member of the cyclase-associated protein family, display a phenotype that establishes CAP1 as a fundamental facilitator of actin dynamics over a wide range of plant tissues. Plants homozygous for cap1 alleles show a reduction in stature and morphogenetic disruption of multiple cell types. Pollen grains exhibit reduced germination efficiency, and cap1 pollen tubes and root hairs grow at a decreased rate and to a reduced length. Live cell imaging of growing root hairs reveals actin filament disruption and cytoplasmic disorganisation in the tip growth zone. Mutant cap1 alleles also show synthetic phenotypes when combined with mutants of the Arp2/3 complex pathway, which further suggests a contribution of CAP1 to in planta actin dynamics. In yeast, CAP interacts with adenylate cyclase in a Ras signalling cascade; but plants do not have Ras. Surprisingly, cap1 plants show disruption in plant signalling pathways required for co-ordinated organ expansion suggesting that plant CAP has evolved to attain plant-specific signalling functions.

A Class I ADP-Ribosylation Factor GTPase-Activating Protein Is Critical for Maintaining Directional Root Hair Growth in Arabidopsis

“…Actin-disrupting drugs inhibited or delocalized root hair growth (Bibikova et al, 1999;Ketelaar et al, 2003), consistent with reports showing that knockouts to the vegetative ACT2 gene in Arabidopsis have distorted root hair morphology (Ringli et al, 2002). Moreover, altering the expression of genes encoding proteins that affect actin turnover, such as profilin, actin-depolymering factor, formin, actininteracting protein, and cyclase-associated protein, disrupted normal root hair development (Ramachandran et al, 2000;Dong et al, 2001;Yi et al, 2005;Deeks et al, 2007;Ketelaar et al, 2007).…”

Root Hairs

“…tip-growth unit (Emons and Ketelaar, 2009). The extreme apex contains a large number of vesicles while other membrane structures are absent from this area (Galway et al, 1997;Ketelaar et al, 2007). Continuous delivery of new vesicles is assisted by cytoplasmic streaming, the mixing cellular contents (Figure 13, Supplementary Movie 1.…”

Self-Incompatibility-Induced Programmed Cell Death in Field Poppy Pollen Involves Dramatic Acidification of the Incompatible Pollen Tube Cytosol

“…CAP sequesters actin monomers, prevents them from polymerization in vitro, and also, promotes the severing of actin filaments in association with ADF (Barrero et al, 2002;Chaudhry et al, 2007;Deeks et al, 2007;Ono, 2013). Plant CAP is likely to be a key regulator of actin dynamics using a mechanism unique to plants Ono, 2013).…”

“…Plant CAP is likely to be a key regulator of actin dynamics using a mechanism unique to plants Ono, 2013). The loss-of-function cap1 mutant in Arabidopsis has major defects in pollen germination and tube growth, with altered actin configuration consistent with a major role for CAP in regulating actin dynamics (Deeks et al, 2007). Regarding a role for pH in regulating plant CAP activity, to our knowledge, there are no data.…”