1,721,700 research outputs found
Functional Identification of OsHk6 as a Homotypic Cytokinin Receptor in Rice with Preferential Affinity for iP
No full textCytokinins are involved in key developmental processes in rice (Oryza sativa), including the regulation of cell proliferation and grain yield. However, the in vivo action of histidine kinases (OsHks), putative cytokinin receptors, in rice cytokinin signaling remains elusive. This study examined the function and characteristics of OsHk3, 4 and 6 in rice. OsHk6 was highly sensitive to isopentenyladenine (iP) and was capable of restoring cytokinin-dependent ARR6 reporter expression in the ahk2 ahk3 Arabidopsis mutant upon treatment with 1 nM iP. OsHk4 recognized trans-zeatin (tZ) and iP, while OsHk3 scarcely induced cytokinin signaling activity. OsHk4 and OsHk6 mediated the canonical two-component signaling cascade of Arabidopsis to induce phosphorylation of ARR2. OsHk4 and OsHk6 were highly expressed in spikelets, suggesting that tZ and iP might play key roles in grain development. OsHk6 formed a self-interacting homomer in rice protoplasts, although the trans-phosphorylation activity between subunits was much lower than the intra-molecular trans-phosphorylation activity. This indicates that the action mechanism of OsHks is evolutionarily diverged from bacterial histidine kinases. Ectopic expression of OsHk6 in rice calli promoted green pigmentation and subsequent shoot induction, further supporting an OsHk6 in planta function as a cytokinin receptor. From the results of this study, OsHks are homomeric cytokinin receptors with distinctive cytokinin preferences in rice.X1119sciescopu
Sorting and anterograde trafficking at the Golgi apparatus
No full textIn general, the basic principles of trafficking systems in plant cells appear to be similar to those in animal and yeast cells, indicating that trafficking mechanisms are highly conserved throughout all eukaryotes (Jurgens, 2004; Vitale and Hinz, 2005). However, there are still considerable variations at the molecular level as well as in applying these basic principles to situations in plant cells, such as multiple vacuole types in a single cell or cell plate formation during cytokinesis (Jurgens, 2004; Jolliffe et al., 2005; Robinson et al., 2005, 2007; Mo et al., 2006). Additionally, the role of the trans-Golgi network (TGN) as the early endosome in plant cells is drastically different from the function of the TGN in animal cells and yeast (Lam et al., 2007). These differences provide compelling reasons to study protein trafficking in plant cells. Earlier studies have focused primarily on the identification of sorting motifs in cargo proteins. However, recent studies have focused more on identification of the molecular players involved in the various steps of trafficking (Jurgens, 2004; Robinson et al., 2007). Detailed studies of the components of these pathways will provide a deeper understanding of these important aspects of plant biology and may elucidate similarities, as well as differences, in trafficking mechanisms between animal and plant cells.X1126sciescopu
S-phase-specific transcription regulatory elements are present in a replication-independent testis-specific H2B histone gene
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Evolution and Design Principles of the Diverse Chloroplast Transit Peptides
No full textChloroplasts are present in organisms belonging to the kingdom Plantae. These organelles are thought to have originated from photosynthetic cyanobacteria through endosymbiosis. During endosymbiosis, most cyanobacterial genes were transferred to the host nucleus. Therefore, most chloroplast proteins became encoded in the nuclear genome and must return to the chloroplast after translation. The N-terminal cleavable transit peptide (TP) is necessary and sufficient for the import of nucleus-encoded interior chloroplast proteins. Over the past decade, extensive research on the TP has revealed many important characteristic features of TPs. These studies have also shed light on the question of how the many diverse TPs could have evolved to target specific proteins to the chloroplast. In this review, we summarize the characteristic features of TPs. We also highlight recent advances in our understanding of TP evolution and provide future perspectives about this important research area.11Nsciescopuskc
Attenuation of cytokinin signaling via proteolysis of a type-B response regulator
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Protein import into chloroplasts via the Tic40-dependent and -independent pathways depends on the amino acid composition of the transit peptide
No full textPreprotein import into chloroplasts is mediated by the coordinated actions of translocons at the outer and inner envelopes of chloroplasts (Toc and Tic, respectively). The cleavable N-terminal transit peptide (TP) of preproteins plays an essential role in the import of preproteins into chloroplasts. The Tic40 protein, a component of the Tic complex, is believed to mediate the import of preproteins through the inner envelope. In this study, we aimed to obtain in vivo evidence supporting the role of Tic40 in pre-protein import into chloroplasts. Contrary to previous findings, the import of various preproteins with wild-type TPs showed no difference between tic40 and wild-type protoplasts of Arabidopsis thaliana. However, the import of N-terminal mutants of the RbcS protein (RbcS-nt), in which basic amino acid residues (arginine and lysine) in the central region of the TP were substituted with neutral (alanine) or acidic (glutamic acid) amino acid residues, was dependent on Tic40. In addition, in tic40 protoplasts, the inner envelope protein Tic40 tagged with HA (hemagglutinin) showed more intermediate form present in the stroma. Based on these results, we propose that protein can be imported into chloroplast by either Tic40-independent or Tic40-dependent pathways depending on the types of TP. (C) 2019 Elsevier Inc. All rights reserved.11Nsciescopu
Targeting and biogenesis of transporters and channels in chloroplast envelope membranes: Unsolved questions
No full textChloroplasts produce carbohydrates, hormones, vitamins, amino acids, pigments, nucleotides, ATP, and secondary metabolites. Channels and transporters are required for the movement of molecules across the two chloroplast envelope membranes. These transporters and channel proteins are grouped into two different types, including beta-barrel proteins and transmembrane-domain (TMD) containing proteins. Most beta-barrel proteins are localized at the outer chloroplast membrane, and TMD-containing proteins are localized at the inner chloroplast membrane. Many of these transporters and channels are encoded by nuclear genes; therefore, they have to be imported into chloroplasts after translation on cytosolic ribosomes. These proteins should have specific targeting signals for their final destination in the chloroplast mernbrane and for assembly into specific complexes. In this review, we summarize recent progress in the identification, functional characterization, and-biogenesis of transporters and channels at the chloroplast envelope membranes, and discuss outstanding questions regarding transporter and channel protein biogenesis. (C) 2014 Elsevier Ltd. All rights reserved.1184sciescopu
A Fight between Plants and Pathogens for the Control of Chloroplasts
No full textChloroplasts are the home of innumerable metabolic pathways for plant growth and environmental responses. Recently, in an issue of Cell, Medina-Puche et al. revealed a novel mechanism by which plant pathogens dampened host defense responses, orchestrated from chloroplasts. This mechanism encompassing the plasma membrane and chloroplasts has likely been established via host-pathogen co-evolution. ? 2020 Elsevier Inc.Chloroplasts are the home of innumerable metabolic pathways for plant growth and environmental responses. Recently, in an issue of Cell, Medina-Puche et al. revealed a novel mechanism by which plant pathogens dampened host defense responses, orchestrated from chloroplasts. This mechanism encompassing the plasma membrane and chloroplasts has likely been established via host-pathogen co-evolution. ? 2020 Elsevier Inc.11Nsciescopu
A Sophisticated Network of Signaling Pathways Regulates Stomatal Defenses to Bacterial Pathogens
Full text linkGuard cells are specialized cells forming stomatal pores at the leaf surface for gas exchanges between the plant and the atmosphere. Stomata have been shown to play an important role in plant defense as a part of the innate immune response. Plants actively close their stomata upon contact with microbes, thereby preventing pathogen entry into the leaves and the subsequent colonization of host tissues. In this review, we present current knowledge of molecular mechanisms and signaling pathways implicated in stomatal defenses, with particular emphasis on plant-bacteria interactions. Stomatal defense responses begin from the perception of pathogen-associated molecular patterns (PAMPs) and activate a signaling cascade involving the production of secondary messengers such as reactive oxygen species, nitric oxide, and calcium for the regulation of plasma membrane ion channels. The analyses on downstream molecular mechanisms implicated in PAMP-triggered stomatal closure have revealed extensive interplays among the components regulating hormonal signaling pathways. We also discuss the strategies deployed by pathogenic bacteria to counteract stomatal immunity through the example of the phytotoxin coronatine.X113626Ysciescopu
Adaptor proteins in protein trafficking between endomembrane compartments in plants
No full textClathrin is a highly conserved coat protein that plays a critical role in lipid vesicle-mediated trafficking at multiple routes in various post-Golgi compartments. It consists of large and small subunits, and exists in the cytosol as triskelions composed of three pairs of small and large subunits. For vesicle formation, the triskelions are recruited to the membrane of specific compartments where they undergo self-polymerization to produce coats for lipid vesicles. However, clathrin has no ability to bind directly to lipid membranes. Therefore, accessory proteins are necessary for its recruitment to the donor compartment where vesicles are formed. A large number of accessory proteins, called adaptor proteins, have been identified and characterized extensively at the molecular and cellular levels in animal cells and yeast. Recently, the roles of many adaptor proteins have been elucidated in plant cells. As expected from the conserved nature of lipidmediated trafficking in eukaryotic cells, these plant adaptor proteins for clathrin show a high degree of functional conservation with those found in animal cells and yeast. At the same time, they are also involved in plant-specific processes such as the transition from the PSV to the lytic vacuole and cell-plate formation. Here, we summarize recent advances in the physiological roles of adaptor proteins in plant cells.X1121sciescopuskc
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