A tobacco gene encoding a novel basic class II chitinase: a putative ancestor of basic class I and acidic class II chitinase genes.
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.
Ohme-Takagi
M
M
Plant Molecular Biology Laboratory, National Institute of Bioscience and Human Technology, Tsukuba, Japan. masaru@nibh.go.jp
Meins
F
F
Shinshi
H
H
D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D020134:Catalytic Domain; D002688:Chitinases / Q000737:chemistry / Q000235:genetics*; D003545:Cysteine; D019143:Evolution, Molecular; D017343:Genes, Plant / Q000235:genetics*; D015698:Genomic Library; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D021382:Protein Sorting Signals; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics*
D021382:Protein Sorting Signals; D002688:Chitinases; D003545:Cysteine