| 1. |
- Ji, Yan, 1987-
(author)
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Regulation of chloroplast development during the greening process
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Upon light exposure, the expression of one-third of the nuclear-encoded genes is changing, including genes encoding many chloroplast-targeted proteins responsible for the initiation of plastid transcription and the establishment of photosynthesis. The control of the nuclear-encoded genes involved in the development of chloroplast is referred to as anterograde signalling. In my thesis work I have focused on both cryptochrome and phytochrome signalling pathways regulating the transcription of photosynthesis-related genes during chloroplast development. The results in the thesis demonstrate that several light-responsive nuclear transcription factors play a direct role in chloroplast development, and reveal the regulatory mechanism underlying the initiation of plastid photosynthetic gene expression. In this thesis, bZIP16 was found as a CRY1 interacting factor. Together with bZIP68 and GBF1, they regulate the expression of LHCBs and SIG5 through a blue light signalling pathway, promoting cotyledon opening and chloroplast development during de-etiolation. These findings provide novel insights into the role of bZIP transcription factors during chloroplast development with the involvement of the cryptochrome signalling pathway. To further investigate how the plastid photosynthetic gene expression is initiated, I focused on the role of two plastid RNA polymerases, nuclear-encoded plastid RNA polymerase (NEP) and plastid-encoded plastid RNA polymerase (PEP). By combining the PIF3-binding motif analysis, mathematic modelling and photoreceptor mutant analysis, we demonstrated a PHYB-PIF3 mediated regulation of the initial expression of the nuclear-encoded PEP components, SIGs and PAPs with the G-box/PBE-box as potential PIF3 binding-site. I have also demonstrated the presence of a fully assembled PEP complex in both proplastids and etioplasts using 2D BN/SDS-PAGE and its importance for the basal level of psaA and psbA transcription in darkness and during the early light response.
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| 2. |
- Lepisto, A., et al.
(author)
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Deletion of chloroplast NADPH-dependent thioredoxin reductase results in inability to regulate starch synthesis and causes stunted growth under short-day photoperiods
- 2013
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In: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 64:12, s. 3843-3854
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Journal article (peer-reviewed)abstract
- Plastid-localized NADPH-dependent thioredoxin reductase C (NTRC) is a unique NTR enzyme containing both reductase and thioredoxin domains in a single polypeptide. Arabidopsis thaliana NTRC knockout lines (ntrc) show retarded growth, especially under short-day (SD) photoperiods. This study identified chloroplast processes that accounted for growth reduction in SD-acclimated ntrc. The strongest reduction in ntrc growth occurred under photoperiods with nights longer than 14h, whereas knockout of the NTRC gene did not alter the circadian-clock-controlled growth of Arabidopsis. Lack of NTRC modulated chloroplast reactive oxygen species (ROS) metabolism, but oxidative stress was not the primary cause of retarded growth of SD-acclimated ntrc. Scarcity of starch accumulation made ntrc leaves particularly vulnerable to photoperiods with long nights. Direct interaction of NTRC and ADP-glucose pyrophosphorylase, a key enzyme in starch synthesis, was confirmed by yeast two-hybrid analysis. The ntrc line was not able to maximize starch synthesis during the light period, which was particularly detrimental under SD conditions. Acclimation of Arabidopsis to SD conditions also involved an inductive rise of ROS production in illuminated chloroplasts that was not counterbalanced by the activation of plastidial anti-oxidative systems. It is proposed that knockout of NTRC challenges redox regulation of starch synthesis, resulting in stunted growth of the mutant lines acclimated to the SD photoperiod.
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| 3. |
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| 4. |
- Nikkanen, L., et al.
(author)
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Thioredoxin-dependent regulatory networks in chloroplasts under fluctuating light conditions
- 2014
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In: Philosophical Transactions of the Royal Society B-Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 369:1640
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Journal article (peer-reviewed)abstract
- Plants have adopted a number of mechanisms to restore redox homeostasis in the chloroplast under fluctuating light conditions in nature. Chloroplast thioredoxin systems are crucial components of this redox network, mediating environmental signals to chloroplast proteins. In the reduced state, thioredoxins control the structure and function of proteins by reducing disulfide bridges in the redox active site of a protein. Subsequently, an oxidized thioredoxin is reduced by a thioredoxin reductase, the two enzymes together forming a thioredoxin system. Plant chloroplasts have versatile thioredoxin systems, including two reductases dependent on ferredoxin and NADPH as reducing power, respectively, several types of thioredoxins, and the system to deliver thiol redox signals to the thylakoid membrane and lumen. Light controls the activity of chloroplast thioredoxin systems in two ways. First, light reactions activate the thioredoxin systems via donation of electrons to oxidized ferredoxin and NADP(+), and second, light induces production of reactive oxygen species in chloroplasts which deactivate the components of the thiol redox network. The diversity and partial redundancy of chloroplast thioredoxin systems enable chloroplast metabolism to rapidly respond to ever-changing environmental conditions and to raise plant fitness in natural growth conditions.
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| 5. |
- Spetea, Cornelia, 1968, et al.
(author)
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Changing the light environment: chloroplast signalling and response mechanisms
- 2014
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In: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 369:1640
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Research review (peer-reviewed)abstract
- Light is an essential environmental factor required for photosynthesis, but it also mediates signals to control plant development and growth and induces stress tolerance. The photosynthetic organelle (chloroplast) is a key component in the signalling and response network in plants. This theme issue of Philosophical Transactions of the Royal Society of London B: Biology provides updates, highlights and summaries of the most recent findings on chloroplast-initiated signalling cascades and responses to environmental changes, including light and biotic stress. Besides plant molecular cell biology and physiology, the theme issue includes aspects from the cross-disciplinary fields of environmental adaptation, ecology and agronomy.
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| 6. |
- Toivola, J., et al.
(author)
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Overexpression of chloroplast NADPH-dependent thioredoxin reductase in Arabidopsis enhances leaf growth and elucidates in vivo function of reductase and thioredoxin domains
- 2013
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In: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 4
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Journal article (peer-reviewed)abstract
- Plant chloroplasts have versatile thioredoxin systems including two thioredoxin reductases and multiple types of thioredoxins. Plastid-localized NADPH-dependent thioredoxin reductase (NTRC) contains both reductase (NTRd) and thioredoxin (TRXd) domains in a single polypeptide and forms homodimers. To study the action of NTRC and NTRC domains in vivo, we have complemented the ntrc knockout line of Arabidopsis with the wild type and full-length NTRC genes, in which 2-Cys motifs either in NTRd, or in TRXd were inactivated. The ntrc line was also transformed either with the truncated NTRd or TRXd alone. Overexpression of wild-type NTRC promoted plant growth by increasing leaf size and biomass yield of the rosettes. Complementation of the ntrc line with the full-length NTRC gene containing an active reductase but an inactive TRXd, or vice versa, recovered wild-type chloroplast phenotype and, partly, rosette biomass production, indicating that the NTRC domains are capable of interacting with other chloroplast thioredoxin systems. Overexpression of truncated NTRd or TRXd in ntrc background did not restore wild-type phenotype. Modeling of the three-dimensional structure of the NTRC dimer indicates extensive interactions between the NTR domains and the TRX domains further stabilize the dimeric structure. The long linker region between the NTRd and TRXd, however, allows flexibility for the position of the TRXd in the dimer. Supplementation of the TRXd in the NTRC homodimer model by free chloroplast thioredoxins indicated that TRXf is the most likely partner to interact with NTRC. We propose that overexpression of NTRC promotes plant biomass yield both directly by stimulation of chloroplast biosynthetic and protective pathways controlled by NTRC and indirectly via free chloroplast thioredoxins. Our data indicate that overexpression of chloroplast thiol redox-regulator has a potential to increase biofuel yield in plant and algal species suitable for sustainable bioenergy production.
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