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JXB Advance Access originally published online on July 31, 2008
Journal of Experimental Botany 2008 59(12):3475-3484; doi:10.1093/jxb/ern197
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Brassica juncea chitinase BjCHI1 inhibits growth of fungal phytopathogens and agglutinates Gram-negative bacteria

Yuanfang Guan1, Sathishkumar Ramalingam1 *, Dinesh Nagegowda1, Paul W. J. Taylor2 and Mee-Len Chye1,{dagger}

1School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China
2BioMarka, School of Agriculture and Food Systems, The University of Melbourne, Victoria 3010, Australia

{dagger} To whom correspondence should be addressed. E-mail: mlchye{at}hkucc.hku.hk

Brassica juncea BjCHI1 is a plant chitinase with two chitin-binding domains. Its expression, induced in response to wounding, methyl jasmonate treatment, Aspergillus niger infection, and caterpillar Pieris rapae feeding, suggests that it plays a role in defence. In this study, to investigate the potential of using BjCHI1 in agriculture, Pichia-expressed BjCHI1 and its deletion derivatives that lack one or both chitin-binding domains were tested against phytopathogenic fungi and bacteria. Transplastomic tobacco expressing BjCHI1 was also generated and its extracts assessed. In radial growth-inhibition assays, BjCHI1 and its derivative with one chitin-binding domain showed anti-fungal activities against phytopathogens, Colletotrichum truncatum, C. acutatum, Botrytis cinerea, and Ascochyta rabiei. BjCHI1 also inhibited spore germination of C. truncatum. Furthermore, BjCHI1, but not its derivatives lacking one or both domains, inhibited the growth of Gram-negative bacteria (Escherichia coli, Ralstonia solanacearum, Pseudomonas aeruginosa) more effectively than Gram-positive bacteria (Micrococcus luteus and Bacillus megaterium), indicating that the duplicated chitin-binding domain, uncommon in chitinases, is essential for bacterial agglutination. Galactose, glucose, and lactose relieved agglutination, suggesting that BjCHI1 interacts with the carbohydrate components of the Gram-negative bacterial cell wall. Retention of chitinase and bacterial agglutination activities in transplastomic tobacco extracts implicates that BjCHI1 is potentially useful against both fungal and bacterial phytopathogens in agriculture.

Key words: Bacterial agglutination, chitin-binding domain, chloroplast transformation, Indian mustard, lectin, phytopathogens, Pichia-expressed proteins, transplastomic tobacco

* Present address: Department of Biotechnology, Bharathiar University, Coimbatore, Tamilnadu, India

Received 17 May 2008; Revised 2 July 2008 Accepted 3 July 2008


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