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The LeATL6-Associated Ubiquitin/Proteasome System May Contribute to Fungal Elicitor-Activated Defense Response via the Jasmonic Acid-Dependent Signaling Pathway in Tomato

January 2007 , Volume 20 , Number  1
Pages  72 - 81

Daisuke Hondo , 1 Shu Hase , 1 Yoshinori Kanayama , 2 Nobuyuki Yoshikawa , 3 Shigehito Takenaka , 4 and Hideki Takahashi 1

1Department of Life Science, and 2Department of Biological Resource Sciences, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan; 3Faculty of Agriculture, Iwate University, Morioka 020-8550, Japan; 4Department of Upland Agriculture, National Agricultural Research Center for Hokkaido Region, Hokkaido 082-0071, Japan

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Accepted 18 July 2006.

The expression of LeATL6, an ortholog of Arabidopsis ATL6 that encodes a RING-H2 finger protein, was induced in tomato roots treated with a cell wall protein fraction (CWP) elicitor of the biocontrol agent Pythium oligandrum. The LeATL6 protein was expressed as a fusion protein with a maltose-binding protein (MBP) in Escherichia coli, and it catalyzed the transfer of ubiquitin to the MBP moiety on incubation with ubiquitin, the ubiquitin-activating enzyme E1, and the ubiquitin-conjugating enzyme E2; this indicated that LeATL6 represents ubiquitin ligase E3. LeATL6 expression also was induced by elicitor treatment of jai1-1 mutant tomato cells in which the jasmonic acid (JA)-mediated signaling pathway was impaired; however, JA-dependent expression of the basic PR-6 and TPI-1 genes that encode proteinase inhibitor II and I, respectively, was not induced in elicitor-treated jai1-1 mutants. Furthermore, transient overexpression of LeATL6 under the control of the Cauliflower mosaic virus 35S promoter induced the basic PR6 and TPI-1 expression in wild tomato but not in the jai1-1 mutant. In contrast, LeATL6 overexpression did not activate salicylic acid-responsive acidic PR-1 and PR-2 promoters in wild tomato. These results indicated that elicitor-responsive LeATL6 probably regulates JA-dependent basic PR6 and TPI-1 gene expression in tomato. The LeATL6-associated ubiquitin/proteasome system may contribute to elicitor-activated defense responses via a JA-dependent signaling pathway in plants.

Additional keywords: ATL gene family, induced resistance, Micro-Tom.

© 2007 The American Phytopathological Society