Effects of lead nitrate (LN), a hepatic mitogen, on hepatic gene expressions of lanosterol 14alpha-demethylase (CYP51) and the sterol regulatory element binding proteins (SREBP-1a, SREBP-1c and SREBP-2), which are thought to be transcription factors for hepatic CYP51 gene, were examined by the methods of Northern blot and/or real time reverse transcriptase-polymerase chain reaction (RT-PCR). In both immature (4-week-old) and mature (7-week-old) rats, LN treatment resulted in definite increases in hepatic gene expression of CYP51 at 12 h and in the liver weight at 48 h. As for transcription factors for the CYP51 gene, enhanced gene expression of SREBP-2 was observed 6-12 h after LN treatment, whereas no enhanced gene expression of other SREBPs, SREBP-1a and SREBP-1c, was observed at any time after the treatment; for SREBP-1a, there was no significant change; for SREPB-1c, there was a drastic decrease. In addition, the serum total cholesterol level was increased 12 h after LN treatment to 7-week-old rats, and the increased level was maintained at least up to 48 h later. In the present study, we demonstrate for the first time that LN, a heavy-metal ion, activates the expression of the SREBP-2 and CYP51 genes without decreasing the serum total cholesterol level and further suggest that only SREBP-2 among SREBPs might play an important role in the LN-enhanced CYP51 gene expression.
Phytohormone abscisic acid (ABA) plays a key role in stomata closure, osmostress acclimation, and vegetative and embryonic dormancy. Group B3 Raf protein kinases (B3-Rafs) serve as positive regulators of ABA and osmostress signaling in the moss Physcomitrium patens and the angiosperm Arabidopsis thaliana. While P. patens has a single B3-Raf called ARK, specific members of B3-Rafs among six paralogs regulate ABA and osmostress signaling in A. thaliana, indicating functional diversification of B3-Rafs in angiosperms. However, we found that the liverwort Marchantia polymorpha, belonging to another class of bryophytes, has three paralogs of B3-Rafs, MpARK1, MpARK2, and MpARK3, with structural variations in the regulatory domains of the polypeptides. By reporter assays of the P. patens ark line and analysis of genome-editing lines of M. polymorpha, we found that these B3-Rafs are functionally redundant in ABA response, with respect to inhibition of growth, tolerance to desiccation and expression of stress-associated transcripts, the majority of which are under the control of the PYR/PYL/RCAR-like receptor MpPYL1. Interestingly, gemmae in gemma cups were germinating only in mutant lines associated with MpARK1, indicating that dormancy in the gametophyte is controlled by a specific B3-Raf paralog. These results indicated not only conservation of the role of B3-Rafs in ABA and osmostress response in liverworts but also functional diversification of B3-Rafs, which is likely to have occurred in the early stages of land plant evolution.
for sharing their wisdom with us during this research. In addition, we also thank Dr Sanjay Saint for his remarkable diagnostic guidance and Mr Jason Engle for his English advice.Contributors TW and NY cared for the patient. TW supervised NY for her physical examination. TW wrote the draft. AG revised the draft.
SummaryDormancy is a key process for land plants to adapt drastically changing terrestrial environment. The liverwort Marchantia polymorpha produce dormant propagules called gemmae for asexual reproduction. The plant hormone abscisic acid (ABA) plays significant roles in the regulation of dormancy in both seed of flowering plants and gemma of M. polymorpha.Based on the previous transcriptome analysis, here we identified the basic helix-loop-helix transcription factor MpHYPNOS (MpHYP), as a key regulator of gemma dormancy.The knock-out mutants showed much higher germination rate of gemmae in gemma cup than ABA-related mutants did, while the growth and development were the same as wild type. Transient induction of MpHYP caused irreversible growth arrest in gemma and thallus. Transcriptome and qRT-PCR analyses revealed that MpHYP repressed cell-cycle related genes and induced the ABA biosynthesis and responsive genes. Indeed, ABA amounts were increased or decreased by overexpression or knock-out of MpHYP, respectively. However, the growth arrest caused by MpHYP overexpression was not suppressed by the mutation in the ABA receptor gene.These data suggest that MpHYP regulates gemma dormancy and thallus growth partially through the ABA pathway. Our findings would provide the clues to understand ABA-dependent and independent regulation of dormancy in land plants.
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