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.

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The preparations of (K0.5Na0.5)NbO3 (KNN)‐based ceramics were studied as lead‐free piezoelectric materials. The authors found that the addition of CuO greatly enhanced the sinterability of the KNN‐based ceramics. The sinterability and piezoelectric properties of these ceramics were dependent upon the A/B ratio, CuO doping, and the formation of a solid solution with KTaO3. Perovskite (K0.5Na0.5)xNbO3 (x=A/B ratio) was synthesized with A/B ratios of 1.00 and 1.05 by CuO doping, while (K0.5Na0.5)NbO3 contained K4CuNb8O23 as a second phase with A/B ratios below 0.98. Although the A site‐rich (K0.5Na0.5)NbO3 (x=1.00 and 1.05) ceramics exhibited deliquescence, the A site‐poor (K0.5Na0.5)NbO3 (x≤0.98) ceramics with K4CuNb8O23 had higher densities without deliquescence. K4CuNb8O23 also improved Qm, which reached 1400 for the (K0.5Na0.5)1.0NbO3 doped with 0.5 mol% K4CuNb8O23. The formation of a solid solution with KTaO3 raised the melting point of the system and also improved its sinterability. The kp and Qm of (K0.5Na0.5)0.97(Nb0.95Ta0.05)O3 with CuO were 0.41 and 1400, respectively.

The positioning of peroxisomes in a cell is a regulated process that is closely associated with their functions. Using this feature of the peroxisomal positioning as a criterion, we identified three Arabidopsis thaliana mutants (peroxisome unusual positioning1 [peup1], peup2, and peup4) that contain aggregated peroxisomes. We found that the PEUP1, PEUP2, and PEUP4 were identical to Autophagy-related2 (ATG2), ATG18a, and ATG7, respectively, which are involved in the autophagic system. The number of peroxisomes was increased and the peroxisomal proteins were highly accumulated in the peup1 mutant, suggesting that peroxisome degradation by autophagy (pexophagy) is deficient in the peup1 mutant. These aggregated peroxisomes contained high levels of inactive catalase and were more oxidative than those of the wild type, indicating that peroxisome aggregates comprise damaged peroxisomes. In addition, peroxisome aggregation was induced in wild-type plants by exogenous application of hydrogen peroxide. The cat2 mutant also contained peroxisome aggregates. These findings demonstrate that hydrogen peroxide as a result of catalase inactivation is the inducer of peroxisome aggregation. Furthermore, an autophagosome marker, ATG8, frequently colocalized with peroxisome aggregates, indicating that peroxisomes damaged by hydrogen peroxide are selectively degraded by autophagy in the wild type. Our data provide evidence that autophagy is crucial for quality control mechanisms for peroxisomes in Arabidopsis.

Background: A leaf‐variegated mutation var1 of Arabidopsis results in the development of abnormal plastids and the formation of a green/white sector. Genetic analysis of the var1 mutant indicated that it acts synergistically with another mutation var2, suggesting that the two genes are relevant. The VAR2 locus has been shown to encode a chloroplastic FtsH, an ATP‐dependent protease which is possibly involved in the degradation of thylakoid proteins and plastid development. Results: In this study we show that the VAR1 locus encodes a chloroplastic FtsH protein homologous to VAR2. VAR1 contains a conserved motif for ATPase and a metalloprotease characteristic to FtsH proteins, and is targeted into chloroplasts. A VAR1‐fusion protein synthesized in vitro exhibited ATPase activity and partial metalloprotease activity. The maximum yield of photochemistry, measured by chlorophyll fluorescence, showed that the var1 mutants were sensitive to photoinhibitory light exposure at 800 µmol/m2/s. Conclusion: VAR1 and VAR2 comprise an FtsH small gene family together with other FtsH genes in Arabidopsis. VAR1 as well as VAR2 may play an important role in degrading photodamaged subunits in photosystem II. Loss of VAR1 and VAR2 perhaps impairs the photoprotection mechanism and thylakoid development, causing leaf variegation as a consequence.

Superparamagnetic nanoparticles (SPIONs) could enable cancer theranostics if magnetic resonance imaging (MRI) and magnetic hyperthermia treatment (MHT) were combined. However, the particle size of SPIONs is smaller than the pores of fenestrated capillaries in normal tissues because superparamagnetism is expressed only at a particle size <10 nm. Therefore, SPIONs leak from the capillaries of normal tissues, resulting in low accumulation in tumors. Furthermore, MHT studies have been conducted in an impractical way: direct injection of magnetic materials into tumor and application of hazardous alternating current (AC) magnetic fields. To accomplish effective enhancement of MRI contrast agents in tumors and inhibition of tumor growth by MHT with intravenous injection and a safe AC magnetic field, we clustered SPIONs not only to prevent their leakage from fenestrated capillaries in normal tissues, but also for increasing their relaxivity and the specific absorption rate. We modified the clusters with folic acid (FA) and polyethylene glycol (PEG) to promote their accumulation in tumors. SPION clustering and cluster modification with FA and PEG were achieved simultaneously via the thiol-ene click reaction. Twenty-four hours after intravenous injection of FA- and PEG-modified SPION nanoclusters (FA-PEG-SPION NCs), they accumulated locally in cancer (not necrotic) tissues within the tumor and enhanced the MRI contrast. Furthermore, 24 h after intravenous injection of the NCs, the mice were placed in an AC magnetic field with H = 8 kA/m and f = 230 kHz (Hf = 1.8×109 A/m∙s) for 20 min. The tumors of the mice underwent local heating by application of an AC magnetic field. The temperature of the tumor was higher than the surrounding tissues by ≈6°C at 20 min after treatment. Thirty-five days after treatment, the tumor volume of treated mice was one-tenth that of the control mice. Furthermore, the treated mice were alive after 12 weeks; control mice died up to 8 weeks after treatment.

Plastids undergo drastic morphological and physiological changes under different developmental stages and in response to environmental conditions. A key to accomplishing these transitions and maintaining homeostasis is the quality and quantity control of many plastid proteins by proteases and chaperones. Although a limited number of plastid proteases have been identified by biochemical approaches, recent progress in genome information revealed various plant proteases that are of prokaryotic origin and that are localized in chloroplasts. Of these, ATP-dependent proteases such as Clp, FtsH, and Lon are considered the major enzymes involved in processive degradation (gradual degradation to oligopeptides and amino acids). The basic architecture of plant ATP-dependent proteases is very similar to the architechture of bacterial enzymes, such as those in Escherichia coli, but plastid enzymes apparently have extraordinary numbers of isomers. Recent molecular genetic characterization in Arabidopsis has identified differential roles of these isomers. This review covers what is currently known about the types and function of plastid proteases together with our new observations.

Variegated leaves are often caused by a nuclear recessive mutation in higher plants. Characterization of the gene responsible for variegation has shown to provide several pathways involved in plastid differentiation. Here we describe an Arabidopsis variegated mutant isolated by T-DNA tagging. The mutant displayed green and yellow sectors in all green tissues except for cotyledons. Cells in the yellow sector of the mutant contained both normal-appearing and mutant chloroplasts. The isolated mutant was shown to be an allele of the previously reported mutant, yellow variegated (var2). Cloning and molecular characterization of the VAR2 locus revealed that it potentially encodes a chloroplastic homologue of FtsH, an ATP-dependent metalloprotease that belongs to a large protein family involved in various cellular functions. ftsH-like genes appear to comprise a small gene family in Arabidopsis genome, since at least six homologues were found in addition to VAR2. Dispensability of VAR2 was therefore explained by the redundancy of genes coding for FstHs. In the yellow regions of the mutant leaves, accumulation of photosynthetic protein components in the thylakoid membrane appeared to be impaired. Based on the role of FtsH in a protein degradation pathway in plastids, we propose a possibility that VAR2 is required for plastid differentiation by avoiding partial photooxidation of developing chloroplasts.