βC1, the pathogenicity factor of TYLCCNV, interacts with AS1 to alter leaf development and suppress selective jasmonic acid responses

Abstract

Viruses induce pathogenic symptoms on plants but the molecular basis is poorly understood. Here, we show that transgenic Arabidopsis expressing the pathogenesis protein ␤C1 of Tomato yellow leaf curl China virus (TYLCCNV), a geminivirus, can phenocopy to a large extent disease symptoms of virus-infected tobacco plants in having upward curled leaves, radialized leaves with outgrowth tissues from abaxial surfaces, and sterile flowers. These morphological changes are paralleled by a reduction in miR165/166 levels and an increase in PHB and PHV transcript levels. Two factors, ASYMMETRIC LEAVES 1 (AS1) and ASYMMETRIC LEAVES 2 (AS2), are known to regulate leaf development as AS1/AS2 complex. Strikingly, ␤C1 plants phenocopy plants overexpressing AS2 at the morphological and molecular level and ␤C1 is able to partially complement as2 mutation. ␤C1 binds directly to AS1, elicits morphological and gene expression changes dependent on AS1 but not AS2, and attenuates expression of selective jasmonic acid (JA)-responsive gene. Our results show that ␤C1 forms a complex with AS1 to execute its pathogenic functions and to suppress a subset of JA responses.[Keywords: Geminivirus; asymmetric leaves 1; asymmetric leaves 2; jasmonic acid; silencing suppressor; whitefly] Supplemental material is available at http://www.genesdev.org.

Tomato SlSnRK1 Protein Interacts with and Phosphorylates βC1, a Pathogenesis Protein Encoded by a Geminivirus β-Satellite

“…We demonstrated previously that transgenic N. benthamiana, tobacco, and Arabidopsis plants expressing the TYLCCNB bC1 gene are stunted and show leaf cupping and curling. The resulting "symptoms" are much more severe than those associated with TYLCCNV plus TYLCCNB infection, demonstrating that bC1 is very toxic to plants (Cui et al, 2004;Yang et al, 2008). SnRK1 phosphorylation of bC1 may be used by plants to overcome its detrimental effects.…”

“…In addition, protein phosphorylation often plays a role in ubiquitin-mediated proteolysis, and SCF (one type of multisubunit ubiquitin-protein ligase [E3]) degradation pathways are mediated by phosphorylation-dependent substrate recognition (Kong and Chock, 1992;Clurman et al, 1996;Won and Reed, 1996;Musti et al, 1997;Willems et al, 1999;Pickart, 2001;Feng et al, 2004;Gao et al, 2004;Dreher and Callis, 2007). The recent discovery that bC1 protein is degraded by the 26S proteasome (Yang et al, 2008) indicates that SlSnRK1 may interact with and phosphorylate bC1 for degradation by the 26S proteasome, leading to the attenuation of symptoms and reduction of the efficiency of viral infection.…”

“…bC1 is a pathogenicity determinant and a suppressor of RNA silencing (Jose and Usha, 2003;Cui et al, 2004Cui et al, , 2005Saunders et al, 2004;Qian and Zhou, 2005;Saeed et al, 2005;Gopal et al, 2007;Kon et al, 2007). Previous studies showed that bC1 interacts with ASYMMETRIC LEAVES1 to alter leaf development and suppress selected jasmonic acid responses (Yang et al, 2008). bC1 also interacts with a host ubiquitinconjugating enzyme, SlUBC3, and modifies the host ubiquitination system (Eini et al, 2009).…”

HISTONE DEACETYLASE6 Interacts with FLOWERING LOCUS D and Regulates Flowering in Arabidopsis

“…These results indicate that HDA6 is directly associated with FLD. For coimmunoprecipitation assay, a tobacco (Nicotiana benthamiana) transient expression system was used (Yang et al, 2008). Tobacco leaves were infiltrated with Agrobacterium cultures carrying 35S:GFP-HDA6 and 35S:Myc-FLD, and leaf extracts were analyzed by coimmunoprecipitation.…”

“…The pull-down assay was performed as described previously (Yang et al, 2008) with some modifications. For GST pull-down, GST and GST-HDA6 recombinant proteins were incubated with 30 mL of GST resin in a binding buffer (50 mM Tris-Cl, pH 7.5, 100 mM NaCl, 0.25% Triton X-100, and 35 mM b-mercaptoethanol) for 2 h at 4°C, the binding reaction was washed three times with the binding buffer, and then the FLD-His recombinant protein was added and incubated for an additional 2 h at 4°C.…”