Tobacco-expressed Brassica juncea chitinase BjCHI1 shows antifungal activity in vitro.
We have previously isolated a Brassica juncea cDNA encoding BjCHI1, a novel chitinase with two chitin-binding domains, and have shown that its mRNA is induced by wounding and methyl jasmonate treatment (K.-J. Zhao and M.-L. Chye, Plant Mol. Biol. 40 (1999) 1009-1018). By the presence of two chitin-binding domains, BjCHI1 resembles the precursor of UDA (Urtica dioica agglutinin) but, unlike UDA, BjCHI1 retains its chitinase catalytic domain after post-translational processing. Here, we indicate the role of BjCHI1 in plant defense by demonstrating its mRNA induction upon Aspergillus niger infection or caterpillar Pieris rapae (L.) feeding. To further investigate the biological properties of BjCHI1, we transformed tobacco with a construct expressing the BjCHI1 cDNA from the CaMV 35S promoter. Subsequently, we purified BjCHI1 from the resultant transgenic Ro plants using a regenerated chitin column followed by fast protein liquid chromatography (FPLC). Also, the significance of the second chitin-binding domain in BjCHI1 was investigated by raising transgenic tobacco plants expressing BjCHI2, a deletion derivative of BjCHI1 lacking one chitin-binding domain. Colorimetric chitinase assays at 25 degrees C, pH 5, showed no significant differences between the activities of BjCHI1 and BjCHI2, suggesting that chitinase activity, due to the catalytic domain, is not enhanced by the presence of a second chitin-binding domain. Both BjCHI1 and BjCHI2 show in vitro anti-fungal activity toward Trichoderma viride, causing reductions in hyphal diameter, hyphal branching and conidia size.
Fung
King-Leung
KL
Department of Botany, University of Hong Kong, Hong Kong, China.
Zhao
Kai-Jun
KJ
He
Zhu-Mei
ZM
Chye
Mee-Len
ML
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001937:Brassica / Q000201:enzymology* / Q000382:microbiology / Q000469:parasitology; D002080:Butterflies / Q000502:physiology; D002686:Chitin / Q000378:metabolism; D002688:Chitinases / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D005247:Feeding Behavior / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D030821:Plants, Genetically Modified; D010957:Plasmids / Q000235:genetics; D011485:Protein Binding; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D017384:Sequence Deletion; D014026:Nicotiana / Q000235:genetics*; D014242:Trichoderma / Q000187:drug effects* / Q000254:growth & development
D011994:Recombinant Proteins; D002686:Chitin; D002688:Chitinases