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Suppression of Tobacco Basic Chitinase Gene Expression in Response to Colonization by the Arbuscular Mycorrhizal Fungus Glomus intraradices

June 1998 , Volume 11 , Number  6
Pages  489 - 497

Rakefet David , 1 Hanan Itzhaki , 2 Idit Ginzberg , 1 Yedidya Gafni , 1 Gad Galili , 2 and Yoram Kapulnik 1

1Institute of Field and Garden Crops, ARO, The Volcani Center, Bet Dagan 50250, Israel; and 2Department of Plant Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel

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Accepted 28 February 1998.

A differentially displayed cDNA clone (MD17) was isolated from tobacco roots (Nicotiana tabacum cv. Xanthi-nc) infected with the arbuscular mycorrhizal (AM) fungus Glomus intraradices. The isolated DNA fragment exhibited a reduced level of expression in response to AM establishment and 90% identity with the 3′ noncoding sequence of two basic chitinases (EC from N. tabacum. Northern (RNA) blots and Western blots (immunoblots), probed with tobacco basic chitinase gene-specific probe and polyclonal antibodies raised against the chitinase enzyme, yielded hybridization patterns similar to those of MD17. Moreover, the up-regulation of the 32-kDa basic chitinase gene expression in tobacco roots by (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) was less effective in mycorrhizal roots than in nonmycorrhizal controls. Suppression of endogenous basic chitinase (32-kDa) expression was also observed in transgenic mycorrhizal plants that constitutively express the 34-kDa basic chitinase A isoform. When plants were grown with an increased phosphate supply, no suppression of the 32-kDa basic chitinase was obtained. These findings indicate that during the colonization and establishment of G. intraradices in tobacco roots, expression of the basic chitinase gene is down-regulated at the mRNA level.

Additional keywords: pathogen-related (PR) proteins, symbiosis.

© 1998 The American Phytopathological Society