Tyramine accumulation in rice cells caused a dwarf phenotype via reduced cell division |
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Authors: | Young Soon Kim Sangkyu Park Kiyoon Kang Kyungjin Lee Kyoungwhan Back |
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Institution: | (1) Department of Biotechnology, Interdisciplinary Program of Graduate School for Bioenergy and Biomaterials, Bioenegry Research Center, College of Agriculture and Life Sciences, Chonnam National University, Gwangju, 500-757, South Korea; |
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Abstract: | Transgenic rice plants overexpressing a rice tyrosine decarboxylase (TyDC) exhibited a dwarf phenotype with a high level of tyramine accumulation. The height of transgenic rice was reduced on average
to 35% of the wild-type height, whereas the number of tillers increased to 190% that of wild type. When judged by cellular
distribution of tyramine and tyramine derivatives, the level of tyramine in soluble and insoluble fractions was higher than
that of tyramine derivatives such as 4-coumaroyltyramine (CT) in the transgenic rice plants, suggesting that tyramine rather
than its derivatives was a causative compound triggering the dwarf phenotype. Microscopic observation revealed that cell size
in the transgenic lines was maintained, with a slightly irregular arrangement in the leaf mesophyll cells. When wild-type
rice seeds were grown in the presence of tyramine, rice seedlings also showed stunted phenotypes in a dose-dependent manner.
When these stunted seedlings were employed to measure the degree of cellular proliferation by bromodeoxyuridine incorporation,
only small numbers of cells were found to retain labeled nuclei in shoot tips compared with the untreated control. These results
show that the dwarf phenotype associated with tyramine accumulation in transgenic rice plants is attributable to a reduction
in cell number rather than cell size. In addition, our dwarf phenotype caused by tyramine was not closely associated with
known dwarf genes such as D88. |
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