Toshiharu Shikanai

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During photosynthesis, plants must control the utilization of light energy in order to avoid photoinhibition. We isolated an Arabidopsis mutant, pgr5 (proton gradient regulation), in which downregulation of photosystem II photochemistry in response to intense light was impaired. PGR5 encodes a novel thylakoid membrane protein that is involved in the(More)
Photosynthesis provides at least two routes through which light energy can be used to generate a proton gradient across the thylakoid membrane of chloroplasts, which is subsequently used to synthesize ATP. In the first route, electrons released from water in photosystem II (PSII) are eventually transferred to NADP+ by way of photosystem I (PSI). This linear(More)
Major copper proteins in the cytoplasm of plant cells are plastocyanin, copper/zinc superoxide dismutase, and cytochrome c oxidase. Under copper limited conditions, expression of copper/zinc superoxide dismutase is down-regulated and the protein is replaced by iron superoxide dismutase in chloroplasts. We present evidence that a micro-RNA, miR398, mediates(More)
Expression of miR398 is induced in response to copper deficiency and is involved in the degradation of mRNAs encoding copper/zinc superoxide dismutase in Arabidopsis thaliana. We found that SPL7 (for SQUAMOSA promoter binding protein-like7) is essential for this response of miR398. SPL7 is homologous to Copper response regulator1, the transcription factor(More)
The light reactions in photosynthesis convert light energy into chemical energy in the form of ATP and drive the production of NADPH from NADP+. The reactions involve two types of electron flow in the chloroplast. While linear electron transport generates both ATP and NADPH, photosystem I cyclic electron transport is exclusively involved in ATP synthesis.(More)
To evaluate the physiological significance of cyclic electron flow around photosystem (PS) I, we used a reverse genetic approach to focus on 11 chloroplast genes that encode homologs of mitochondrial complex I subunits (ndhA-K). Since their discovery, the exact function of the respiratory components in plant chloroplasts has been a matter of discussion. We(More)
RNA editing is a process of RNA maturation involved in the insertion, deletion or modification of nucleotides. In organellar transcripts of higher plants, specific cytidine residues are converted into uridine residues. In many cases, editing results in the restoration of conserved amino acid residues, a process that is essential for protein function in(More)
Copper delivery to the thylakoid lumen protein plastocyanin and the stromal enzyme Cu/Zn superoxide dismutase in chloroplasts is required for photosynthesis and oxidative stress protection. The copper delivery system in chloroplasts was characterized by analyzing the function of copper transporter genes in Arabidopsis thaliana. Two mutant alleles were(More)
Cells at the elongation zone expand longitudinally to form the straight central axis of plant stems, hypocotyls and roots, and transverse cortical microtubule arrays are generally recognized to be important for the anisotropic growth. Recessive mutations in either of two Arabidopsis thaliana SPIRAL loci, SPR1 or SPR2, reduce anisotropic growth of endodermal(More)
The chloroplast NAD(P)H dehydrogenase (NDH) complex is involved in photosystem I (PSI) cyclic and chlororespiratory electron transport in higher plants. Although biochemical and genetic evidence for its subunit composition has accumulated, it is not enough to explain the complexes putative activity of NAD(P)H-dependent plastoquinone reduction. We analyzed(More)