Progress 09/01/02 to 08/31/04
Outputs
Sterols are important not only for structural components of eukaryotic cell membranes but also for biosynthetic precursors of steroid hormones. In plants, the diverse functions of sterol-derived brassinosteroids (BRs) in growth and development have been investigated rigorously, yet little is known about the regulatory roles of other phytosterols. Recent analysis of Arabidopsis fackel (fk) mutants and cloning of the FK gene that encodes a sterol C-14 reductase have indicated that sterols play a crucial role in plant cell division, embryogenesis and development. Nevertheless, the molecular mechanism underlying the regulatory role of sterols in plant development has not been revealed. Results of this project demonstrated that both sterols and BR are active regulators of plant development and gene expression. Similar to BR, both typical (sitosterol and stigmasterol) and atypical (8,14-diene sterols accumulated in fk mutants) sterols affect the expression of genes involved
in cell expansion and cell division. The regulatory function of sterols in plant development is further supported by a phenocopy of the fk mutant using a sterol C-14 reductase inhibitor, fenpropimorph. Although fenpropimorh impairs cell expansion and affects gene expression in a dose-dependent manner, neither effect can be corrected by applying exogenous BR. These results provide strong evidence that sterols are essential for normal plant growth and development and that there is likely a BR-independent sterol response pathway in plants. On the basis of the expression of endogenous FK and a reporter gene FK::GUS, we have found that FK is up regulated by several growth promoting hormones including brassinolide, implicating a possible hormone crosstalk between sterol and other hormone signaling pathways.
Impacts
Our studies have opened up a new area of research in plant biology. The understanding of the basic molecular and cellular mechanism of sterol function is expected to contribute to the development of biotechnology for crop improvement.
Publications
- He, J. X., Fujioka, S., Li, T.-C., Kang, S. G., Seto, H., Takatsuto, S., Yoshida, S., and Jang, J.-C. (2003) Sterols regulate development and gene expression in Arabidopsis thaliana. Plant Physiol. 131:1258-1269.
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Progress 01/01/03 to 12/31/03
Outputs
Sterols are part of the vast family of isoprenoids- a group of structurally related secondary metabolites. These compounds are essential for both animals and plants because they are membrane components and as such regulate cellular functions. The best-known sterol is cholesterol, whose signaling functions in cell division, cell growth, cell death, and various developmental processes are studied extensively in animals. Whereas plants also produce dozens of different sterols, including cholesterol, only brassinosteroids derived from campesterol have been shown to act as hormone signals in post-embryonic development. Other sterols produced by a branch pathway have been considered mainly as membrane structural components. However, we have recently identified a novel patterning mutant called fackel in Arabidopsis thaliana, a model plant species for molecular genetic research. Plants defective in FACKEL gene exhibit not only dwarfed growth but also altered pattern of
development such as abnormal shape and size of embryos and organs. We have cloned the FACKEL gene and found it encodes a sterol C-14 reductase that is involved in the production of both BR and other sterols. These results have led us to postulate that besides BR, other sterols are acting as critical signals in the control of both embryonic and post-embryonic development. To further support this hypothesis, we have recently demonstrated that sterols are active regulators of plant development and gene expression. In particular, we have demonstrated that both sterols and BR are active regulators of plant development and gene expression. Similar to BR, both typical (sitosterol and stigmasterol) and atypical (8,14-diene sterols accumulated in fk mutants) sterols affect the expression of genes involved in cell expansion and cell division. The regulatory function of sterols in plant development is further supported by a phenocopy of the fk mutant using a sterol C-14 reductase inhibitor,
fenpropimorph. Although fenpropimorh impairs cell expansion and affects gene expression in a dose-dependent manner, neither effect can be corrected by applying exogenous BR. These results provide strong evidence that sterols are essential for normal plant growth and development and that there is likely a BR-independent sterol response pathway in plants. On the basis of the expression of endogenous FK and a reporter gene FK::GUS, we have found that FK is up regulated by several growth promoting hormones including brassinolide, implicating a possible hormone crosstalk between sterol and other hormone signaling pathways.
Impacts
Our studies have opened up a new area of research in plant biology. The understanding of the basic molecular and cellular mechanism of sterol function is expected to contribute to the development of biotechnology for crop improvement.
Publications
- He, J. X., Fujioka, S., Li, T.-C., Kang, S. G., Seto, H., Takatsuto, S., Yoshida, S., and Jang, J.-C. (2003) Sterols regulate development and gene expression in Arabidopsis thaliana. Plant Physiol. 131:1258-1269.
- Mlller, A.R., J.C. Jang and N.J. Flickinger. 2003. The effect of commercial Brassinosteroid on growth and steroidal glycoalkaloid content of cultivated potato (Solanum tuberosum) And. Acta Hort. 619:309-313.
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Progress 01/01/02 to 12/31/02
Outputs
Sterols are part of the vast family of isoprenoids- a group of structurally related secondary metabolites. These compounds are essential for both animals and plants because they are membrane components and as such regulate cellular functions. The best-known sterol is cholesterol, whose signaling functions in cell division, cell growth, cell death, and various developmental processes are studied extensively in animals. Whereas plants also produce dozens of different sterols, including cholesterol, only brassinosteroids derived from campesterol have been shown to act as hormone signals in post-embryonic development. Other sterols produced by a branch pathway have been considered mainly as membrane structural components. However, we have recently identified a novel patterning mutant called fackel in Arabidopsis thaliana, a model plant species for molecular genetic research. Plants defective in FACKEL gene exhibit not only dwarfed growth but also altered pattern of
development such as abnormal shape and size of embryos and organs. We have cloned the FACKEL gene and found it encodes a sterol C-14 reductase that is involved in the production of both BR and other sterols. These results have led us to postulate that besides BR, other sterols are acting as critical signals in the control of both embryonic and post-embryonic development. To further support this hypothesis, we have recently demonstrated that sterols are active regulators of plant development and gene expression. In particular, we have found that sterols can affect the expression of genes involved in cell expansion and cell division. We have re-created the fackel mutant phenotype in normal plants using a sterol C-14 reductase inhibitor, fenpropimorph. Although fenpropimorh impairs cell expansion and affects gene expression, neither one of the effects can be corrected by the application of brassinosteroids. These results provide strong evidence that sterols are essential for normal plant
growth and development and that BR cannot substitute the function of sterols in plants.
Impacts
Our studies have opened up a new area of research in plant biology. The understanding of the basic molecular and cellular mechanism of sterol function is expected to contribute to the development of biotechnology for crop improvement
Publications
- No publications reported this period
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