A tobacco gene encoding a novel basic class II chitinase: a putative ancestor of basic class I and acidic class II chitinase genes |
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Authors: | M. Ohme-Takagi F. Meins Jr. H. Shinshi |
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Affiliation: | (1) Plant Molecular Biology Laboratory National Institute of Bioscience and Human Technology 1-1 Higashi, Tsukuba 305-0046, Japan Fax: +81-298-54-6095; e-mail: masaru@nibh.go.jp, JP;(2) Friedrich Miescher-Institute, Postfach 2543, CH-4002 Basel, Switzerland, CH |
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Abstract: | Various chitinases have been identified in plants and categorized into several groups based on the analysis of their sequences and domains. We have isolated a tobacco gene that encodes a predicted polypeptide consisting of a 20-amino acid N-terminal signal peptide, followed by a 245-amino acid chitinolytic domain. Although the predicted mature protein is basic and shows greater sequence identity to basic class I chitinases (75%) than to acidic class II chitinases (67%), it lacks the N-terminal cysteine-rich domain and the C-terminal vacuolar targeting signal that is diagnostic for class I chitinases. Therefore, this gene appears to encode a novel, basic, class II chitinase, which we have designated NtChia2;B1. Accumulation of Chia2;B1 mRNA was induced in leaves in association with the local-lesion response to tobacco mosaic virus (TMV) infection, and in response to treatment with salicylic acid, but was only slightly induced by treatment with ethephon. Little or no Chia2;B1 mRNA was detected in roots, flowers, and cell-suspension cultures, in which class I chitinase mRNAs accumulate to high concentrations. Sequence comparisons of Chia2;B1 with known tobacco class I and class II chitinase genes suggest that Chia2;B1 might encode an ancestral prototype of the present-day class I and class II isoforms. Possible mechanisms for chitinase gene evolution are discussed. Received: 25 May 1998 / Accepted: 29 June 1998 |
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Keywords: | Chitinase Tobacco Transposition Evolution |
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