SGT1b

Plant defense responses need to be tightly regulated to prevent auto-immunity, which is detrimental to growth and development. To identify negative regulators of Resistance (R) protein-mediated resistance, we screened for mutants with constitutive defense responses in the npr1-1 background. Map-based cloning revealed that one of the mutant genes encodes a conserved TPR domain-containing protein previously known as SRFR1 (SUPPRESSOR OF rps4-RLD). The constitutive defense responses in the srfr1 mutants in Col-0 background are suppressed by mutations in SNC1, which encodes a TIR-NB-LRR (Toll Interleukin1 Receptor-Nucleotide Binding-Leu-Rich Repeat) R protein...

• Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) causes an economically important bacterial speck disease on tomato and produces symptoms with necrotic lesions surrounded by chlorosis. The chlorosis is mainly attributed to a jasmonic acid (JA)-isoleucine analogue, coronatine (COR), produced by Pst DC3000. However, the molecular processes underlying lesion development and COR-induced chlorosis are poorly understood. • In this study, we took advantage of a chlorotic phenotype elicited by COR on Nicotiana benthamiana leaves and virus-induced gene silencing (VIGS) as a rapid reverse genetic screening tool and identified a role for SGT1 (suppressor of G2 allele of skp1) in COR-induced chlorosis...

SUMMARY Within the last 10 years, numerous R genes have been cloned from natural genetic variation in model as well as crop plants, and these have been classified according to their motifs. Some of the downstream signalling components have also been identified by artificial mutagenesis. Recently, cloning of three of these signalling genes (COI1, RAR1 and SGT1b) from Arabidopsis, barley and tobacco have helped uncover the physiological link between defence signalling and ubiquitin-mediated protein degradation...

Low temperature is one of environmental factors that restrict plant growth homeostasis and plant-pathogen interactions. Recent studies suggest a link between temperature responses and defense responses; however, the underlying molecular mechanisms remain unclear. In this study, the chilling sensitive 3 (chs3-1) mutant in Arabidopsis was characterized. chs3-1 plants showed arrested growth and chlorosis when grown at 16 degrees C or when shifted from 22 to 4 degrees C. chs3-1 plants also exhibited constitutively activated defense responses at 16 degrees C, which were alleviated at a higher temperature (22 degrees C)...

*The hairpin-based RNA interference (RNAi) technique plays an important role in exploring gene function in plants. Although there are several methods for making hairpin RNA (hpRNA) constructs, these methods usually need multiple relatively laborious, time-consuming or high-cost cloning steps. Here we describe a one-step, zero-background ligation-independent cloning (OZ-LIC) method for making intron-containing hpRNA (ihpRNA) constructs by our vector pRNAi-LIC. *To generate the ihpRNA constructs with zero-background, this method only requires treating two PCR products of target gene flanked with different LIC sequences and SmaI-linearized pRNAi-LIC vector by T4 DNA polymerase respectively, and then transforming these treated DNA mixture into Escherichia coli...

The lesion-mimic Arabidopsis mutant, syp121 syp122, constitutively expresses the salicylic acid (SA) signaling pathway and has low penetration resistance to powdery mildew fungi. Genetic analyses of the lesion-mimic phenotype have expanded our understanding of programmed cell death (PCD) in plants. Inactivation of SA signaling genes in syp121 syp122 only partially rescues the lesion-mimic phenotype, indicating that additional defenses contribute to the PCD. Whole genome transcriptome analysis confirmed that SA-induced transcripts, as well as numerous other known pathogen-response transcripts, are up-regulated after inactivation of the syntaxin genes...

In plants, resistance to necrotrophic pathogens depends on the interplay between different hormone systems, such as those regulated by salicylic acid (SA), jasmonic acid (JA), ethylene, and abscisic acid. Repression of auxin signaling by the SA pathway was recently shown to contribute to antibacterial resistance. Here, we demonstrate that Arabidopsis auxin signaling mutants axr1, axr2, and axr6 that have defects in the auxin-stimulated SCF (Skp1-Cullin-F-box) ubiquitination pathway exhibit increased susceptibility to the necrotrophic fungi Plectosphaerella cucumerina and Botrytis cinerea...

The cell wall protein fraction (CWP) is purified from the non-pathogenic biocontrol agent Pythium oligandrum and is composed of two glycoproteins (POD-1 and POD-2), which are structurally similar to class III elicitins. In tomato plants treated with CWP, jasmonic acid (JA)- and ethylene (ET)-dependent signaling pathways are activated, and resistance to Ralstonia solanaceraum is enhanced. To dissect CWP-induced defense mechanisms, we investigated defense gene expression and resistance to bacterial pathogens in Arabidopsis thaliana ecotype Col-0 treated with CWP...

Fusarium culmorum causes ear blight disease on cereal crops resulting in considerable losses to grain yield, quality and safety. This fungus can also infect Arabidopsis floral tissues. In this study, the Arabidopsis floral infection model was used to assess the impact of five defence mutants on disease.Fusarium culmorum was spray inoculated onto the floral tissues of the mutantseds1, lms1, rar1, sgt1a and sgt1b involved in basal and resistance gene-mediated defence to pathogens. Floral disease development was assessed quantitatively...

The conserved eukaryotic protein SGT1 (for Suppressor of G2 allele of skp1) has characteristics of an HSP90 (for heat shock protein 90 kD) cochaperone and in plants regulates hormone responses and Resistance gene-triggered immunity. We affinity-purified SGT1-interacting proteins from Arabidopsis thaliana leaf extracts and identified by mass spectrometry cytosolic heat shock cognate 70 (HSC70) chaperones as the major stable SGT1 interactors. Arabidopsis SGT1a and SGT1b proteins associate with HSC70 in vivo and distribute with HSC70 in the cytosol and nucleus...

A gain-of-function mutation in resistance (R) gene SSI4 causes constitutive activation of defense responses, spontaneous necrotic lesion formation, enhanced resistance against virulent pathogens, and a severe dwarf phenotype. Genetic analysis revealed that ssi4-induced H(2)O(2) accumulation and spontaneous cell death require RAR1, whereas ssi4-mediated stunting is dependent on SGT1b. By contrast, both RAR1 and SGT1b are required in a genetically additive manner for ssi4-induced disease resistance, SA accumulation, and lesion formation after pathogen infection...

SGT1 (for suppressor of G2 allele of skp1) and RAR1 (for required for Mla12 resistance) are highly conserved eukaryotic proteins that interact with the molecular chaperone HSP90 (for heat shock protein90). In plants, SGT1, RAR1, and HSP90 are essential for disease resistance triggered by a number of resistance (R) proteins. Here, we present structural and functional characterization of plant SGT1 proteins. Random mutagenesis of Arabidopsis thaliana SGT1b revealed that its CS (for CHORD-SGT1) and SGS (for SGT1 specific) domains are essential for disease resistance...

Plant defences require a multitude of tightly regulated resistance responses. In Arabidopsis, the unique gain-of-function mutant suppressor of npr1-1 constitutive 1 (snc1) carries a point mutation in a Resistance (R)-gene, resulting in constitutive activation of defence responses without interaction with pathogens. This has allowed us to identify various downstream signalling components essential in multiple defence pathways. One mutant that suppresses snc1-mediated constitutive resistance is modifier of snc1 5 (mos5), which carries a 15-bp deletion in UBA1, one of two ubiquitin-activating enzyme genes in Arabidopsis...

We show that oomycete-derived Nep1 (for necrosis and ethylene-inducing peptide1)-like proteins (NLPs) trigger a comprehensive immune response in Arabidopsis thaliana, comprising posttranslational activation of mitogen-activated protein kinase activity, deposition of callose, production of nitric oxide, reactive oxygen intermediates, ethylene, and the phytoalexin camalexin, as well as cell death. Transcript profiling experiments revealed that NLPs trigger extensive reprogramming of the Arabidopsis transcriptome closely resembling that evoked by bacteria-derived flagellin...

Although a wide range of structurally diverse small molecules can act as auxins, it is unclear whether all of these compounds act via the same mechanisms that have been characterized for 2,4-dichlorophenoxyacetic acid (2,4-D) and indole-3-acetic acid (IAA). To address this question, we used a novel member of the picolinate class of synthetic auxins that is structurally distinct from 2,4-D to screen for Arabidopsis (Arabidopsis thaliana) mutants that show chemically selective auxin resistance. We identified seven alleles at two distinct genetic loci that conferred significant resistance to picolinate auxins such as picloram, yet had minimal cross-resistance to 2,4-D or IAA...

We isolated a lesion mimic mutant, necrotic spotted lesions 1 (nsl1), from Ds-tagged Arabidopsis thaliana accession No-0. The nsl1 mutant exhibits a growth retardation phenotype and develops spotted necrotic lesions on its rosette and cauline leaves. These phenotypes occur in the absence of pathogens indicating that nsl1 mutants may constitutively express defense responses. Consistent with this idea, nsl1 accumulates high levels of callose and autofluorescent phenolic compounds localized to the necrotic lesions...

Virus-induced gene silencing (VIGS) offers a rapid and high throughput technique platform for the analysis of gene function in plants. Although routinely used in some Solanaceous species, VIGS system has not been well established in Arabidopsis thaliana (L.) Heynh. We have recently reported some factors that potentially influence tobacco rattle virus (TRV)-mediated VIGS of phytoene desaturase (PDS) and actin gene expression in Arabidopsis. In this study, we have further established that the Agrobacterium strain used for agro-inoculation significantly affects the VIGS efficiency...

A highly conserved eukaryotic protein SGT1 binds specifically to the molecular chaperone, HSP90. In plants, SGT1 positively regulates disease resistance conferred by many Resistance (R) proteins and developmental responses to the phytohormone, auxin. We show that silencing of SGT1 in Nicotiana benthamiana causes a reduction in steady-state levels of the R protein, Rx. These data support a role of SGT1 in R protein accumulation, possibly at the level of complex assembly. In Arabidopsis, two SGT1 proteins, AtSGT1a and AtSGT1b, are functionally redundant early in development...

Many plant developmental and stress responses require the coordinated interaction of the jasmonate and other signalling pathways, such as those for ethylene, salicylic acid and abscisic acid. Recent research in Arabidopsis has uncovered several key players that regulate crosstalk between these signalling pathways and that shed light on the molecular mechanisms modulating this coordinated interaction. Genes that are involved in the regulation of protein stability through the ubiquitin-proteasome pathway (COI1, AXR1 and SGT1b), signalling proteins (MPK4) and transcription factors (AtMYC2, ERF1, NPR1 and WRKY70) form a regulatory network that allows the plant to fine-tune specific responses to different stimuli...

One of tumor escape mechanisms from the host's immunosurveillance system (i.e., a haplotype loss of HLA class I antigens) has been detected in various tumor cells. We hypothesize that the majority of tumor cells with normal HLA class I expression were attacked and eradicated by CTLs, and only a minority with an abnormal expression of HLA class I antigens could escape the host's immunosurveillance system. Using HLA class I-transfected tumor variants as stimulators in A904L lung cancer cell line, which has a haplotype loss of HLA class I antigens, both the transfected HLA-A26 and HLA-B39-restricted CTL lines were induced from autologous lymphocytes...