The Mi-1-Mediated Pest Resistance Requires Hsp90 and Sgt1  

Abstract

The tomato (Solanum lycopersicum) Mi-1 gene encodes a protein with putative coiled-coil nucleotide-binding site and leucine-rich repeat motifs. Mi-1 confers resistance to root-knot nematodes (Meloidogyne spp.), potato aphids (Macrosiphum euphorbiae), and sweet potato whitefly (Bemisia tabaci). To identify genes required in the Mi-1-mediated resistance to nematodes and aphids, we used tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) to repress candidate genes and assay for nematode and aphid resistance. We targeted Sgt1 (suppressor of G-two allele of Skp1), Rar1 (required for Mla12 resistance), and Hsp90 (heat shock protein 90), which are known to participate early in resistance gene signaling pathways. Two Arabidopsis (Arabidopsis thaliana) Sgt1 genes exist and one has been implicated in disease resistance. Thus far the sequence of only one Sgt1 ortholog is known in tomato. To design gene-specific VIGS constructs, we cloned a second tomato Sgt1 gene, Sgt1-2. The gene-specific VIGS construct TRV-SlSgt1-1 resulted in lethality, while silencing Sgt1-2 using TRV-SlSgt1-2 did not result in lethal phenotype. Aphid and root-knot nematode assays of Sgt1-2-silenced plants indicated no role for Sgt1-2 in Mi-1-mediated resistance. A Nicotiana benthamiana Sgt1 VIGS construct silencing both Sgt1-1 and Sgt1-2 yielded live plants and identified a role for Sgt1 in Mi-1-mediated aphid resistance. Silencing of Rar1 did not affect Mi-1-mediated nematode and aphid resistance and demonstrated that Rar1 is not required for Mi-1 resistance. Silencing Hsp90-1 resulted in attenuation of Mi-1-mediated aphid and nematode resistance and indicated a role for Hsp90-1. The requirement for Sgt1 and Hsp90-1 in Mi-1-mediated resistance provides further evidence for common components in early resistance gene defense signaling against diverse pathogens and pests.

Ripening-Regulated Susceptibility of Tomato Fruit toBotrytis cinereaRequiresNORBut NotRINor Ethylene

“…HSP90 is required for Mi resistance in tomato (Bhattarai et al, 2007), and Hsc70 is involved in tomato responses to Ralstonia solanacearum (Byth et al, 2001). Most of the other genes induced by infection of MG or RR fruit have unknown functions.…”

Novel resistance mechanisms of a wild tomato against the glasshouse whitefly

“…Zarate et al (2007)). The only R (resistance) gene in tomato which has been shown to interact with any whitefly species to date is the Mi-1.2 gene (which encodes a protein with putative coiled-coil nucleotide-binding site and leucine-rich repeat motifs; Bhattarai et al (2007)) which has been shown to confer resistance to B. tabaci in tomato, as well as the root-knot nematode and potato aphid (Nombela et al 2003). RNA transcripts of jasmonate and ethylene-responsive pathogenesis-related (PR) proteins, such as the glucanase GluB, the chitinase Chi9 and Pathogenesis-related protein-1, have been shown to accumulate in infested tomato leaves in response to feeding by B. tabaci and T. vaporariorum nymphs, indicating a role for these proteins in tomato whitefly resistance (Puthoff et al 2010).…”

Differential Requirement of Oryza sativa RAR1 in Immune Receptor-Mediated Resistance of Rice to Magnaporthe oryzae

“…The function of these proteins in disease resistance responses have been extensively investigated previously using mutant analyses Chandra-Shekara et al, 2004;Hubert el al., 2003;Lu et al, 2003;Shirasu et al, 1999;Takahashi et al, 2003) and by virus induced gene silencing (VIGS) analyses in several plant species (Bhattarai et al, 2007;de la Fuente van Bentem et al, 2005;Leister et al, 2005;Liu et al, 2004;Scofield et al, 2005). The data from these studies revealed differing specificities for these proteins in diverse NB-LRR-mediated resistance responses.…”