| 1. |
- Baba, Kyoko, et al.
(författare)
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Activity-dormancy transition in the cambial meristem involves stage-specific modulation of auxin response in hybrid aspen.
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:8, s. 3418-23
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Tidskriftsartikel (refereegranskat)abstract
- The molecular basis of short-day-induced growth cessation and dormancy in the meristems of perennial plants (e.g., forest trees growing in temperate and high-latitude regions) is poorly understood. Using global transcript profiling, we show distinct stage-specific alterations in auxin responsiveness of the transcriptome in the stem tissues during short-day-induced growth cessation and both the transition to and establishment of dormancy in the cambial meristem of hybrid aspen trees. This stage-specific modulation of auxin signaling appears to be controlled via distinct mechanisms. Whereas the induction of growth cessation in the cambium could involve induction of repressor auxin response factors (ARFs) and down-regulation of activator ARFs, dormancy is associated with perturbation of the activity of the SKP-Cullin-F-box(TIR) (SCF(TIR)) complex, leading to potential stabilization of repressor auxin (AUX)/indole-3-acetic acid (IAA) proteins. Although the role of hormones, such as abscisic acid (ABA) and gibberellic acid (GA), in growth cessation and dormancy is well established, our data now implicate auxin in this process. Importantly, in contrast to most developmental processes in which regulation by auxin involves changes in cellular auxin contents, day-length-regulated induction of cambial growth cessation and dormancy involves changes in auxin responses rather than auxin content.
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| 2. |
- Baba, Kyoko, et al.
(författare)
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Organellar gene transcription and early seedling development are affected in the rpoT;2 mutant of Arabidopsis.
- 2004
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Ingår i: Plant J. - 0960-7412. ; 38:1, s. 38-48
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Tidskriftsartikel (refereegranskat)abstract
- An Arabidopsis mutant that exhibited reduced root length was isolated from a population of activation-tagged T-DNA insertion lines in a screen for aberrant root growth. This mutant also exhibited reduced hypocotyl length as well as a delay in greening and altered leaf shape. Molecular genetic analysis of the mutant indicated a single T-DNA insertion in the gene RpoT;2 encoding a homolog of the phage-type RNA polymerase (RNAP), that is targeted to both mitochondria and plastids. A second T-DNA-tagged allele also showed a similar phenotype. The mutation in RpoT;2 affected the light-induced accumulation of several plastid mRNAs and proteins and resulted in a lower photosynthetic efficiency. In contrast to the alterations in the plastid gene expression, no major effect of the rpoT;2 mutation on the accumulation of examined mitochondrial gene transcripts and proteins was observed. The rpoT;2 mutant exhibited tissue-specific alterations in the transcript levels of two other organelle-directed nuclear-encoded RNAPs, RpoT;1 and RpoT;3. This suggests the existence of cross-talk between the regulatory pathways of the three RNAPs through organelle to nucleus communication. These data provide an important information on a role of RpoT;2 in plastid gene expression and early plant development.
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| 3. |
- Druart, Nathalie, et al.
(författare)
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Environmental and hormonal regulation of the activity–dormancy cycle in the cambial meristem involves stage-specific modulation of transcriptional and metabolic networks
- 2007
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Ingår i: The Plant Journal. ; 50, s. 557-73
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Tidskriftsartikel (refereegranskat)abstract
- We have performed transcript and metabolite profiling of isolated cambial meristem cells of the model tree aspen during the course of their activity–dormancy cycle to better understand the environmental and hormonal regulation of this process in perennial plants. Considerable modulation of cambial transcriptome and metabolome occurs throughout the activity–dormancy cycle. However, in addition to transcription, post-transcriptional control is also an important regulatory mechanism as exemplified by the regulation of cell-cycle genes during the reactivation of cambial cell division in the spring. Genes related to cold hardiness display temporally distinct induction patterns in the autumn which could explain the step-wise development of cold hardiness. Factors other than low temperature regulate the induction of early cold hardiness-related genes whereas abscisic acid (ABA) could potentially regulate the induction of late cold hardiness-related genes in the autumn. Starch breakdown in the autumn appears to be regulated by the ‘short day’ signal and plays a key role in providing substrates for the production of energy, fatty acids and cryoprotectants. Catabolism of sucrose and fats provides energy during the early stages of reactivation in the spring, whereas the reducing equivalents are generated through activation of the pentose phosphate shunt. Modulation of gibberellin (GA) signaling and biosynthesis could play a key role in the regulation of cambial activity during the activity–dormancy cycle as suggested by the induction of PttRGA which encodes a negative regulator of growth in the autumn and that of a GA-20 oxidase, a key gibberellin biosynthesis gene during reactivation in spring. In summary, our data reveal the dynamics of transcriptional and metabolic networks and identify potential targets of environmental and hormonal signals in the regulation of the activity–dormancy cycle in cambial meristem.
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| 4. |
- Kawamuro, Taiki, et al.
(författare)
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AGN X-Ray Irradiation of CO Gas in NGC 2110 Revealed by Chandra and ALMA
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 895:2
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Tidskriftsartikel (refereegranskat)abstract
- We report spatial distributions of the Fe-K alpha line at 6.4 keV and the CO(J = 2-1) line at 230.538 GHz in NGC 2110, which are, respectively, revealed by Chandra and Atacama Large Millimeter/submillimeter Array (ALMA) at 05. A Chandra 6.2-6.5 keV to 3.0-6.0 keV image suggests that the Fe-K alpha emission extends preferentially in a northwest to southeast direction out to 3 '', or similar to 500 pc, on each side. Spatially resolved spectral analyses support this by finding significant Fe-K alpha emission lines only in the northwest and southeast regions. Moreover, their equivalent widths are found to be similar to 1.5 keV, indicative for the fluorescence by nuclear X-ray irradiation as the physical origin. By contrast, CO(J = 2-1) emission is weak therein. For quantitative discussion, we derive ionization parameters by following an X-ray dominated region (XDR) model. We then find them high enough to interpret the weakness as the result of X-ray dissociation of CO and/or H-2. Another possibility also remains that CO molecules follow a superthermal distribution, resulting in brighter emission in higher-J lines. Further follow-up observations are encouraged to draw a conclusion on what predominantly changes the interstellar matter properties and whether the X-ray irradiation eventually affects the surrounding star formation as active galactic nucleus (AGN) feedback.
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| 5. |
- Kawamuro, Taiki, et al.
(författare)
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Hard X-Ray Irradiation Potentially Drives Negative AGN Feedback by Altering Molecular Gas Properties
- 2021
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Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 257:2
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the role of active galactic nucleus (AGN) X-ray irradiation on the interstellar medium (ISM), we systematically analyzed Chandra and Atacama Large Millimeter/submillimeter Array CO (J = 2-1) data for 26 hard X-ray (>10 keV) selected AGNs at redshifts below 0.05. While Chandra unveils the distribution of X-ray-irradiated gas via Fe-K alpha emission, the CO (J = 2-1) observations reveal that of cold molecular gas. At high resolutions less than or similar to 1 '', we derive Fe-K alpha and CO (J = 2-1) maps for the nuclear 2 '' region and for the external annular region of 2 ''-4 '', where 2 '' is similar to 100-600 pc for most of our AGNs. First, focusing on the external regions, we find the Fe-K alpha emission for six AGNs above 2 sigma. Their large equivalent widths (greater than or similar to 1 keV) suggest a fluorescent process as their origin. Moreover, by comparing the 6-7 keV/3-6 keV ratio, as a proxy of Fe-K alpha, and CO (J = 2-1) images for three AGNs with the highest significant Fe-K alpha detections, we find a possible spatial separation. These suggest the presence of X-ray-irradiated ISM and the change in the ISM properties. Next, examining the nuclear regions, we find that (1) the 20-50 keV luminosity increases with the CO (J = 2-1) luminosity; (2) the ratio of CO (J = 2-1)/HCN (J = 1-0) luminosities increases with 20-50 keV luminosity, suggesting a decrease in the dense gas fraction with X-ray luminosity; and (3) the Fe-K alpha-to-X-ray continuum luminosity ratio decreases with the molecular gas mass. This may be explained by a negative AGN feedback scenario: the mass accretion rate increases with gas mass, and simultaneously, the AGN evaporates a portion of the gas, which possibly affects star formation.
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