Plant and Cell Physiology Advance Access originally published online on November 3, 2006
Plant and Cell Physiology 2006 47(12):1641-1652; doi:10.1093/pcp/pcl031
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AtATG Genes, Homologs of Yeast Autophagy Genes, are Involved in Constitutive Autophagy in Arabidopsis Root Tip Cells
1 School of Food and Nutritional Sciences, University of Shizuoka, 52-1 Yada, Suruga, Shizuoka, 422-8526 Japan
2 Division of Molecular Cell Biology, National Institute for Basic Biology, Myodaiji-cho, Okazaki, 444-8585 Japan
* Corresponding author: E-mail, moriyasu{at}u-shizuoka-ken.ac.jp; Fax, +81-54-264-5099.
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Abstract |
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In Arabidopsis root tips cultured in medium containing sufficient nutrients and the membrane-permeable protease inhibitor E-64d, parts of the cytoplasm accumulated in the vacuoles of the cells from the meristematic zone to the elongation zone. Also in barley root tips treated with E-64, parts of the cytoplasm accumulated in autolysosomes and pre-existing central vacuoles. These results suggest that vacuolar and/or lysosomal autophagy occurs constitutively in these regions of cells. 3-Methyladenine, an inhibitor of autophagy, inhibited the accumulation of such inclusions in Arabidopsis root tip cells. Such inclusions were also not observed in root tips prepared from Arabidopsis T-DNA mutants in which AtATG2 or AtATG5, an Arabidopsis homolog of yeast ATG genes essential for autophagy, is disrupted. In contrast, an atatg9 mutant, in which another homolog of ATG is disrupted, accumulated a significant number of vacuolar inclusions in the presence of E-64d. These results suggest that both AtAtg2 and AtAtg5 proteins are essential for autophagy whereas AtAtg9 protein contributes to, but is not essential for, autophagy in Arabidopsis root tip cells. Autophagy that is sensitive to 3-methyladenine and dependent on Atg proteins constitutively occurs in the root tip cells of Arabidopsis.
Keywords: Arabidopsis - Autophagy - Cysteine protease inhibitor - 3-Methyladenine - Root tip cells - Vacuole
Abbreviations: ER, endoplasmic reticulum; GFP, green fluorescent protein; 3-MA, 3-methyladenine; MS, Murashige and Skoog; PAS, pre-autophagosomal structure; RT–PCR, reverse transcription–PCR.
3 These authors contributed equally to this work.
(Received October 4, 2006; Accepted October 25, 2006)
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