Abstract:In tobacco cultivars resistant to tobacco mosaic virus (TMV), infection results in the death of the infected cells accompanying the formation of necrotic lesions. To identify the genes involved in this hypersensitive reaction, we isolated the cDNA of tobacco DS9, the transcript of which decreases before the appearance of necrotic lesions. The DS9 gene encodes a chloroplastic homolog of bacterial FtsH protein, which serves to maintain quality control of some cytoplasmic and membrane proteins. A large quantity o… Show more
“…Three possibilities should be considered. First, the other homologs may have different functions, as suggested in the case of virus infection in tobacco (Seo et al, 2000). A second possibility is that they are expressed only under certain environmental conditions.…”
Section: The Ftsh Protein Family In Higher Plantsmentioning
Arabidopsis YELLOW VARIEGATED1 ( VAR1 ) and VAR2 are separate loci that encode similar chloroplast FtsH proteases. To date, FtsH is the best-characterized protease in thylakoid membranes involved in the turnover of photosynthetic protein complexes. It comprises a protein family that is encoded by 12 different nuclear genes in Arabidopsis. We show here that nine FtsH proteins are located in the chloroplasts. Mutations in either VAR1 or VAR2 cause typical leaf variegation and sensitivity to photoinhibition. By contrast, none of these phenotypes was observed in T-DNA insertion mutants in other ftsH genes ( ftsh1 , ftsh6 , and ftsh8 ) closely related to VAR1 and VAR2 . This finding suggests that VAR1 and VAR2 play a predominant role in the photosystem II repair cycle in thylakoid membranes. By generating VAR1-and VAR2-specific antibodies, we found that loss of either VAR1 or VAR2 results in the decreased accumulation of the other. Thus, the genetic nonredundancy between VAR1 and VAR2 could be attributed to their coordinated regulation at the protein level. These observations led us to examine whether VAR1 and VAR2 form a complex. Sucrose density gradient and gel filtration analyses revealed a complex of ف 400 to 450 kD, probably representing a hexamer. Furthermore, VAR1 and VAR2 were shown to coprecipitate by immunoprecipitation using VAR1-and VAR2-specific antibodies. The majority of VAR1 appears to exist as heterocomplexes with VAR2, whereas VAR2 may be present as homocomplexes as well. Based on these results, we conclude that VAR1 and VAR2 are the major components of an FtsH complex involved in the repair of photodamaged proteins in thylakoid membranes.
“…Three possibilities should be considered. First, the other homologs may have different functions, as suggested in the case of virus infection in tobacco (Seo et al, 2000). A second possibility is that they are expressed only under certain environmental conditions.…”
Section: The Ftsh Protein Family In Higher Plantsmentioning
Arabidopsis YELLOW VARIEGATED1 ( VAR1 ) and VAR2 are separate loci that encode similar chloroplast FtsH proteases. To date, FtsH is the best-characterized protease in thylakoid membranes involved in the turnover of photosynthetic protein complexes. It comprises a protein family that is encoded by 12 different nuclear genes in Arabidopsis. We show here that nine FtsH proteins are located in the chloroplasts. Mutations in either VAR1 or VAR2 cause typical leaf variegation and sensitivity to photoinhibition. By contrast, none of these phenotypes was observed in T-DNA insertion mutants in other ftsH genes ( ftsh1 , ftsh6 , and ftsh8 ) closely related to VAR1 and VAR2 . This finding suggests that VAR1 and VAR2 play a predominant role in the photosystem II repair cycle in thylakoid membranes. By generating VAR1-and VAR2-specific antibodies, we found that loss of either VAR1 or VAR2 results in the decreased accumulation of the other. Thus, the genetic nonredundancy between VAR1 and VAR2 could be attributed to their coordinated regulation at the protein level. These observations led us to examine whether VAR1 and VAR2 form a complex. Sucrose density gradient and gel filtration analyses revealed a complex of ف 400 to 450 kD, probably representing a hexamer. Furthermore, VAR1 and VAR2 were shown to coprecipitate by immunoprecipitation using VAR1-and VAR2-specific antibodies. The majority of VAR1 appears to exist as heterocomplexes with VAR2, whereas VAR2 may be present as homocomplexes as well. Based on these results, we conclude that VAR1 and VAR2 are the major components of an FtsH complex involved in the repair of photodamaged proteins in thylakoid membranes.
“…The function and location of some members of the FtsH-p1 and FtsH-p2 groups have recently been reported. In Arabidopsis, the proteins from these groups are located in the thylakoid membrane and are apparently involved in the light-induced turnover of the Photosystem II D1 protein (FtsH-p1) and thylakoid membrane biogenesis (FtsH-p2) (Lindahl et al, 2000;Chen et al, 2000), while tobacco FtsH-p1 has been associated with the hypersensitive reaction (Seo et al, 2000). The data shown in Table II and Figure 3 indicates that sugarcane EST clusters present high similarity with these proteins.…”
Section: Resultsmentioning
confidence: 96%
“…A second type of thylakoidal FtsH-like protein has been found in tobacco, where it is related to a hypersensitivity response, and in Arabidopsis where it is involved in the light-induced turnover of the Photosystem II D1 protein (Seo et al, 2000;Lindahl et al, 2000). In pea cells, a thylakoid membrane metalloprotease stimulated by zinc ions has been described as being responsible for the degradation of unassembled subunits of the cytochrome b 6 f complex (Ostersetzer and Adam, 1997), this protein might be either an already described FtsH-like protein or a new type of AAA metalloprotease.…”
A phylogenetic analysis of plant FtsH-like proteins was performed using protein sequences from the GENEBANK database and five groups of plant FtsH-like proteins were identified by neighbor-joining analysis. Prediction of the subcellular location of the proteins suggested that two (FtsH-m1 & FtsH-m2) were mitochondrial and three (FtsH-p1, FtsH-p2, FtsH-p3) were plastid targeting. The phylogenetic profile of plant FtsH-like proteins was used to search sugarcane expressed sequence tag (EST) clusters in the SUCEST database. Initially, 153 clusters presenting homology with FtsH-like proteins were recovered, of which 23 were confirmed by a BLAST search in the GENEBANK database and by comparison of their hidropathy index with that of previously described FtsH-like proteins. Sugarcane presented EST clusters in all phylogenetic groups. In silico expression analysis showed that the groups are differentially expressed in sugarcane tissues, with FtsH-p2 and FtsH-m1 presenting increased levels of expression.
“…9). In addition, it has previously been shown that a chloroplast-specific FtsH protease is destabilized during N-mediated resistance against TMV (Seo et al, 2000) and light is required for the timely activation of the HR by N (Chandra-Shekara et al, 2006). Thus, we hypothesize that THF1 inhibits cell death by preventing light-induced damage in the chloroplasts and that inhibition of THF1 accumulation would in turn accelerate the negative effects of such damage, thus promoting cell death.…”
Section: A Potential Role For Thf1 In the Regulation Of Plant Cell Deathmentioning
One branch of plant immunity is mediated through nucleotide-binding/Leu-rich repeat (NB-LRR) family proteins that recognize specific effectors encoded by pathogens. Members of the I2-like family constitute a well-conserved subgroup of NB-LRRs from Solanaceae possessing a coiled-coil (CC) domain at their N termini. We show here that the CC domains of several I2-like proteins are able to induce a hypersensitive response (HR), a form of programmed cell death associated with disease resistance. Using yeast two-hybrid screens, we identified the chloroplastic protein Thylakoid Formation1 (THF1) as an interacting partner for several I2-like CC domains. Co-immunoprecipitations and bimolecular fluorescence complementation assays confirmed that THF1 and I2-like CC domains interact in planta and that these interactions take place in the cytosol. Several HR-inducing I2-like CC domains have a negative effect on the accumulation of THF1, suggesting that the latter is destabilized by active CC domains. To confirm this model, we investigated N9, which recognizes the coat protein of most Tobamoviruses, as a prototypical member of the I2-like family. Transient expression and gene silencing data indicated that THF1 functions as a negative regulator of cell death and that activation of full-length N9 results in the destabilization of THF1. Consistent with the known function of THF1 in maintaining chloroplast homeostasis, we show that the HR induced by N9 is light-dependent. Together, our results define, to our knowledge, novel molecular mechanisms linking light and chloroplasts to the induction of cell death by a subgroup of NB-LRR proteins.
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