| Project/Area Number |
17570036
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
植物生理・分子
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| Research Institution | Kyoto University |
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Principal Investigator |
MOCHIZUKI Nobuyoshi Kyoro University, Department of Botany. Graduate School of Science, Assistant Professor, 大学院理学研究科, 助手 (60280939)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Keywords | plant / signal transduction / chloroplast / organelle / tetrapyrrole / chlorophyll |
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| Research Abstract |
(1) Analysis of new plastid-signaling mutants.
I have isolated over 600 Arabidopsis mutant lines that showed an elevated level of Lhcb expression in the presence of Norflurazon (NF) under the strong light. 23 lines that accumulate less chlorophyll than wild type were allelic to gun5. GUN5 encodes H-subunit of Mg-chelatase that is essential for the conversion of Protoporphyrin IX to Mg-Protoporphyrin IX in plant chlorophyll biosynthesis pathway. These gun5 alleles have missense mutations in the GUN5(CHLH) coding region. I compared the locations of the mutation in GUNS gene and the MgProtoIX levels as well as Lhcb-derepression phenotypes (gun phenotype) in these new gun5 alleles. It became clear that the MgProtoIX levels and gun phenotypes have no significant correlation in some mutant lines. This result is inconsistent with the hypothesis that the accumulation of MgProtoIX inhibit Lhcb expression (Strand et al. 2003).
With regard to the mutants that have no chlorophyll-related phenotypes,
… More
there are at least two different new loci. Further detailed genetic mapping is underway.
(2) Analysis of mutants that have elevated level of MgProtoXI and MgProtoIXme.
S-adenosyl-L-methionine : Mg-protoporphyrin IX methyltransferase (CHLM) and Mg-protoporphyrin IX monomethyl ester oxidative cyclase (CRD1) are the enzymes essential for the chlorophyll synthesis. I tested chlM and crd1 mutant for the accumulation of MgProtoIX and MgProtoIXme. The chIM mutant accumulated 10 times more MgProtoLX than wild type under the normal growth condition. The crd1 mutant had 2-8 fold accumulation of MgProtoIXme than wild type. The Lhcb mRNA level in these mutants are equivalent to that in the wild type. I then tested the MgProtoIX and MgProtoIXme levels in chIM gun5 and crd1 gun5 double mutants. They showed a significant accumulation of MgProtoIX and MgProtoIXme, respectively. In spite of the high level of MgProtoIX and MgProtoIXme in these double mutants, the gun phenotype of chIM gun5 and crd1 gun5 were not suppressed. Contrary to our results, there are some strong evidences that support the idea that MgProtoIX is a potent signaling factor. Firstly, exogenously applied MgProtoIX to the Arabidopsis cell culture repress the Lhcb expression. Secondly, the extremely high level of MgProtoIX and MgProtoIXme accumulation caused by the application of 2, 2'-dipyridyl (inhibitor of CRD1 and Fe-chelatase) can suppress the gun5 phenotype. Detailed analysis of the intracellular MgProtoIX level and its recognition mechanisms is necessary for the understanding plastid-to-nucleus signaling pathways.
My present working hypothesis is as follows; (a) MgProtoIX is a potent signaling factor. (b) Subcellular concentration (localization) of MgProtoIX is important for the plastid signaling. Less
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