2017 Fiscal Year Research-status Report
Molecular mechanism of ethylene on the regulation of haustorium development and function in parasitic plants
| Project/Area Number |
17K15142
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| Research Institution | Nara Institute of Science and Technology |
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Principal Investigator |
Cui Songkui 奈良先端科学技術大学院大学, 研究推進機構, 博士研究員 (20712532)
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| Project Period (FY) |
2017-04-01 – 2019-03-31
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| Keywords | parasitic plant / ethylene / haustorium / parasitism |
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| Outline of Annual Research Achievements |
In pursuit of understanding the role of ethylene in parasitic plant-host plant interaction, the importance and mechanisms of ethylene signaling pathway in controlling haustorium development and function is partially resolved by molecular and cellular experiments. The results achieved in the year showed that Phtheirospermum japonicum does not require ethylene signaling for haustorium initiation, indicating ethylene signaling is not necessary for perception of haustorium inducing factor. In contrast, ethylene signaling is shown to be involved in subsequent haustorium elongation. It shows that haustorium elongation is likely correlated with active proliferation of haustorial apex cells accompanied with the cellular accumulation of auxin. In the absence of host, haustorium elongation terminates within 2 days and this termination process is accompanied with decreased auxin accumulation and proliferation of haustorial apex cells and requires ETR1 and EIN2 mediated ethylene signaling, suggesting the antagonistic role of ethylene and auxin signaling for haustorium development. Infection assay showed that ethylene signaling is required for host tissue invasion, indicating the key role of ethylene signaling in the function of haustorium. In the host side, ethylene biosynthetic genes and ethylene responsive transcription factors were differentially expressed during infection. Furthermore, ethylene-related genes in host are partially required for host invasion by parasitic plants. These reveal that ethylene is the important interplay between host and parasitic plants for parasitism.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Most of the plans proposed in FY2017 were carried out and showed expected results. In details, phenotypic complementation experiment in Pjein2 mutant using genome fragment successfully restored the haustorium phenotype, which validates the SNP detection result using whole genome sequencing and indicates that the mutant phenotype is indeed caused by defects in ethylene signaling. Phenotypic characterization and auxin response marker expression in the wild type and mutant haustoria revealed that haustorium termination in the absence of host is regulated by cell division activity in haustorial apex via crosstalk between auxin and ethylene. Functional test for mutant haustoria revealed unanticipated and essential role of parasitic ethylene signaling for host invasion. An unanticipated role of host ethylene-related genes in parasitism was observed, showing more general function of ethylene in plant parasitism.
Nevertheless, visualization of cellular ethylene response inside haustorium using established ethylene marker EBS promoter fused with GUS and Venus protein did not show any positive result during haustorium development, suggesting that either ethylene signaling activation is independent from EIN3 mediated pathway or EBS is not suitable marker in Phtheirospermum japonicum as opposed to Arabidopsis.
Proposed experiments for measurement of ACC (ethylene precursor) level and transcriptome analysis during haustorium development is initiated at the end of fiscal year and will be carried out soon.
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| Strategy for Future Research Activity |
Major efforts in FY2018 will be put in performing the experiments of transcriptomics and direct ethylene measurement during haustorium development. For transcriptomics, network analysis combined with GO enrichment test will be performed to resolve genetic regulation of haustorium development and transcriptional regulation of ethylene-related genes and also to identify key genes involved in proliferation of haustorial apex cells for modulating haustorium elongation and host invasion, a key process for plant parasitism.
Investigation of ethylene response during haustorium development will be continuously carried out, this time by using EIN2 translocation system. Generation of new ethylene markers is under consideration using the gene expression data from proposed transcriptomic experiment.
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