Reduced Levels of Chloroplast FtsH Protein in Tobacco Mosaic Virus–Infected Tobacco Leaves Accelerate the Hypersensitive Reaction

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 of DS9 protein was found in healthy leaves, whereas the quantity of DS9 protein in infected leaves decreased before the lesions appeared. In transgenic tobacco plants containing less and more DS9 protein than wild-type plants, the necrotic lesions induced by TMV were smaller and larger, respectively, than those on wild-type plants. These results suggest that a decrease in the level of DS9 protein in TMV-infected cells, resulting in a subsequent loss of function of the chloroplasts, accelerates the hypersensitive reaction. INTRODUCTIONThe hypersensitive reaction (HR) is a plant defense system against pathogen attack. HR is defined as the rapid death of infected cells accompanying formation of necrotic lesions in which pathogens are thought to be enclosed (Goodman and Novacky, 1994). The HR of tobacco to tobacco mosaic virus (TMV) occurs in cultivars carrying the resistance gene N ( NN tobacco) but not in cultivars lacking the N gene ( nn tobacco) (Holmes, 1938; Whitham et al., 1994). Induction of the N gene-mediated HR requires the temperature to be below 22 to 26 Њ C (Kassanis, 1952;Shimomura, 1971; Weststeijn, 1981), suggesting that the gene can function at temperatures below this range.We previously observed that when TMV-inoculated leaves were treated with heat shock or actinomycin D, necrotic lesions were induced in not only NN but also in nn tobacco, even at 30 Њ C, a nonpermissive temperature for the N gene (Shimomura and Ohashi, 1971;Ohashi and Shimomura, 1972). In the actinomycin D-treated leaves in which necrotic lesions were induced, the synthesis of nucleic acid in the host plant was greatly suppressed, whereas the synthesis of TMV RNA was suppressed only slightly (Shimomura and Ohashi, 1980). In contrast to treatment with actinomycin D, treatment with other chemicals, including rifampicin, 2-thiouracil, and cycloheximide, which suppress RNA or protein synthesis in both the TMV and the host plant, did not induce necrotic lesions to form (Ohashi and Shimomura, 1972). Given that actinomycin D forms intercalation complexes with DNA, thereby blocking transcription (Waring, 1981), and that heat shock suppresses transcription of housekeeping genes (Lindquist, 1986;Nover et al., 1989), we hypothesized that suppressing the transcription of certain housekeeping genes in NN tobacco plants after infection with TMV could induce the HR.To isolate such candidate genes, we used a synchronous HR-inducing system based on a temperature shift. Incubation at 30 Њ C of TMV-infected NN tobacco leaves results in 1 Curr...

Coordinated Regulation and Complex Formation of YELLOW VARIEGATED1 and YELLOW VARIEGATED2, Chloroplastic FtsH Metalloproteases Involved in the Repair Cycle of Photosystem II in Arabidopsis 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.…”

Mitochondrial and chloroplast localization of FtsH-like proteins in sugarcane based on their phylogenetic profile

“…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.…”

“…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.…”

The Chloroplastic Protein THF1 Interacts with the Coiled-Coil Domain of the Disease Resistance Protein N′ and Regulates Light-Dependent Cell Death

“…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.…”