Plant and Cell Physiology Advance Access originally published online on November 23, 2005
Plant and Cell Physiology 2006 47(1):164-175; doi:10.1093/pcp/pci232
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AtVAM3 is Required for Normal Specification of Idioblasts, Myrosin Cells
1 Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
2 Faculty of Science, Niigata University, Niigata, 950-2181 Japan
3 Department of Cell Biology, National Institute for Basic Biology, Okazaki, 444-8585 Japan
4 Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, 060-0810 Japan
* Corresponding author: E-mail, ihnishi{at}gr.bot.kyoto-u.ac.jp; Fax, +81-75-753-4142.
Myrosin cells in Capparales plants are idioblasts that accumulate thioglucoside glucohydrolase (TGG, also called myrosinase), which hydrolyzes glucosinolates to produce toxic compounds for repelling pests. Here, we show that AtVAM3 is involved in development of myrosin cells. It has been shown that yeast VAM3 is a Qa-SNARE that is involved in vesicle transport of vacuolar proteins and vacuolar assembly. We found that two Arabidopsis atvam3 alleles, atvam3-3 and atvam3-4/ssm, accumulate large amounts of TGG1 and TGG2 that are enzymatically active. An immunogold analysis revealed that TGGs were specifically localized in the vacuole of myrosin cells in atvam3 mutants. This result indicates that TGGs are normally transported to vacuoles in these mutants and that AtVAM3 is not essential for vacuolar transport of the proteins. We developed a staining method with Coomassie brilliant blue that detects myrosin cells in whole leaves by their high TGG content. This method showed that atvam3 leaves have a larger number of myrosin cells than do wild-type leaves. Myrosin cells were scattered along leaf veins in wild-type leaves, while they were abnormally distributed in atvam3 leaves. The mutants developed a network of myrosin cells throughout the leaves: myrosin cells were not only distributed continuously along leaf veins, but were also observed independent of leaf veins. The excess of myrosin cells in atvam3 mutants might be responsible for the abnormal abundance of TGGs and the reduction of elongation of inflorescence stems and leaves in these mutants. Our results suggest that AtVAM3 has a plant-specific function in development of myrosin cells.
5 Present address: Department of Biology, Faculty of Science, Okayama University, Okayama, 700-8530 Japan.
(Received October 22, 2005; Accepted November 15, 2005)
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