Actin-Depolymerizing Factor2-Mediated Actin Dynamics Are Essential for Root-Knot Nematode Infection ofArabidopsis   

Abstract

Reorganization of the actin and microtubule networks is known to occur in targeted vascular parenchymal root cells upon infection with the nematode Meloidogyne incognita. Here, we show that actin-depolymerizing factor (ADF) is upregulated in the giant feeding cells of Arabidopsis thaliana that develop upon nematode infection and that knockdown of a specific ADF isotype inhibits nematode proliferation. Analysis of the levels of transcript and the localization of seven ADF genes shows that five are upregulated in galls that result from the infection and that ADF2 expression is particularly increased between 14 and 21 d after nematode inoculation. Further analysis of ADF2 function in inducible RNA interference lines designed to knock down ADF2 expression reveals that this protein is required for normal cell growth and plant development. The net effect of decreased levels of ADF2 is F-actin stabilization in cells, resulting from decreased F-actin turnover. In nematodeinfected plants with reduced levels of ADF2, the galls containing the giant feeding cells and growing nematodes do not develop due to the arrest in growth of the giant multinucleate feeding cells, which in turn is due to an aberrant actin network.

Nuclear Function of Subclass I Actin-Depolymerizing Factor Contributes to Susceptibility in Arabidopsis to an Adapted Powdery Mildew Fungus

“…Among four Arabidopsis subclass I ADFs, transfer DNA-based null mutant lines are available for ADF1 (SALK_144459), ADF3 (SALK_139265), and ADF4 (Garlic_823_A11.b.1b.Lb3Fa) but not for ADF2 (Clément et al, 2009;Tian et al, 2009). ADF3 is the most abundantly expressed, approximately 3-fold more than the other three ADFs (Ruzicka et al, 2007).…”

“…The mutant adf4 shows increased susceptibility to the bacterial pathogen Pseudomonas syringae pv tomato (Pst) DC3000 avirulent strain carrying AvrPphB but not to virulent Pst or avirulent Pst DC3000 carrying AvrRpt2 or AvrB (Tian et al, 2009;Porter et al, 2012). Arabidopsis ADF2 expression is up-regulated in the giant feeding cells formed during infection by the root-knot nematode, and in plants that show a reduced ADF2 expression level, nematode growth in roots is inhibited (Clément et al, 2009). Barley rpg4-mediated resistance locus 1, which mediates resistance against the stem rust Puccinia graminis f. sp.…”

CASEIN KINASE1-LIKE PROTEIN2 Regulates Actin Filament Stability and Stomatal Closure via Phosphorylation of Actin Depolymerizing Factor

“…The Arabidopsis thaliana genome encodes 11 ADF proteins, which play important roles in various biological processes. ADF4 is involved in innate immune signaling (Tian et al, 2009;Henty-Ridilla et al, 2014); ADF7 promotes pollen tube growth ; and ADF2 is required for cell growth, development, and root-knot nematode infection (Clément et al, 2009). In addition, the 14-3-3 l protein interacts with phosphorylated ADF1 to regulate actin dynamics during hypocotyl elongation .…”

Functional analysis of an auxin-inducible DNA-binding protein gene

“…Immunolocalization experiments were performed according to Cl ement et al 17 with the following modifications: the dilution of primary antibody was 50-fold and the secondary antibody was FITC-labeled goat anti-rabbit (polyclonal AB). Anti-DBP polyclonal antibodies were prepared against a purified fusion protein expressed in Escherichia coli as previous described.…”