Expression of eight different chitinase genes, representing members of five chitinase classes, was studied in Medicago truncatula roots during formation of arbuscular mycorrhiza with Glomus intraradices, nodulation with Rhizobium meliloti, and pathogen attack by Phytophthora megasperma f. sp. medicaginis, Fusarium solani f. sp. phaseoli (compatible interactions with root rot symptoms), Ascochyta pisi (compatible, symptomless), and F. solani f. sp. pisi (incompatible, nonhost interaction). In the compatible plant-pathogen interactions, expression of class I, II, and IV chitinase genes was enhanced. The same genes were induced during nodulation. Transcripts of class I and II chitinase genes accumulated transiently during early stages of the interaction, and transcripts of the class IV chitinase gene accumulated in mature nodules. The pattern of chitinase gene expression in mycorrhizal roots was markedly different: Expression of class I, II, and IV chitinase genes was not enhanced, whereas expression of three class III chitinase genes, with almost no basal expression, was strongly induced. Two of these three (Mtchitinase III-2 and Mtchitinase III-3) were not induced at all in interactions with pathogens and rhizobia. Thus, the expression of two mycorrhiza-specific class III chitinase genes can be considered a hallmark for the establishment of arbuscular mycorrhiza in Medicago truncatula.
Three chitinase isoenzymes, PvChiE, PvChiF, and PvChiC (molecular masses 29, 28, and 27 kD, respectively), were purified from bean (Phaseolus vulgaris L. cv Saxa) roots infected with the funga1 pathogen Fusarium solani f. sp. phaseoli, and their amino acid sequence was partially determined. All sequences from all three isoenzymes exactly matched deduced amino acid sequences of the bean class IV chitinase PvChi4, formerly called PR4. The N terminus of PvChiF mapped to the hinge region, and the N terminus of PvChiC mapped to the catalytic domain of PvChi4. The N terminus of PvChiE was blocked. The appearance of PvChiE, PvChiF, and PvChiC correlated with an increase in protease activity in infected roots, and they could be generated in vitro by mixing extracts with high protease activity with extracts containing high amounts of PvChi4. Extracts from infected roots prepared in the presence of protease inhibitors also contained the processed forms of PvChi4, indicating that processing occurred in planta and not as an artifact of extraction. Processing of PvChi4 was not detected in incompatible interactions with a nonhost strain of F. solani and in symbiotic interactions with Glomus mosseae, and thus may be important only in compatible interactions with F. solani.
We studied the effect of constitutive expression of pathogenesis-related proteins (PRs) in tobacco plants on vesicular-arbuscular mycorrhiza. Tobacco lines genetically transformed to express various PRs constitutively under the control of the cauliflower mosaic virus 35S promoter of tobacco were examined. Immunoblot analysis and activity measurements demonstrated high levels of expression of the PRs in the root systems of the plants. Constitutive expression of the following acidic isoforms of tobacco PRs did not affect the time course or the final level of colonization by the vesicular-arbuscular mycorrhizal fungus Glomus mosseae: PR-1a, PR-3 (؍PR-Q), PR-Q, PR-4, and PR-5. Similarly, constitutive expression of an acidic cucumber chitinase, of a basic tobacco chitinase with and without its vacuolar targeting peptide, of a basic -1,3-glucanase, and of combinations of PR-Q and PR-Q or basic chitinase and basic -1,3-glucanase did not affect colonization by the mycorrhizal fungus. A delay of colonization by G. mosseae was observed in tobacco plants constitutively expressing the acidic isoform of tobacco PR-2, a protein with -1,3-glucanase activity.
Plant roots enter symbiotic as well as pathogenic interactions with fungi in the rhizosphere. We studied the response of bean (Phaseolus vulgaris L. cv. Saxa) roots to infection by the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe and the pathogen Fusarium solani (Mart.) Sacc. f. sp. phaseoli (Burkholder) Snyder & Hansen. In a time‐course study of the symbiotic interaction between bean roots and G. mosseae, covering all stages of mycorrhiza development, we detected little change in the expression of the defence‐related genes chitinase, β‐1,3‐glucanase and phenylalanine ammonia‐lyase compared with non‐mycorrhizal control roots. The only difference observed was a transient increase in chalcone synthase transcripts at later stages of mycorrhizal root colonization. In interactions with the pathogen, a marked induction of chitinase and phenylalanine ammonia‐lyase expression was observed at the level of both the transcripts and enzyme activities. Class I β‐1,3‐glucanase levels strongly increased at the transcript level, but there was little change in the overall β‐1,3‐glucanase enzyme activity. In the non‐host interaction between common bean and Fusarium solani (Mart.) Sacc. f. sp. pisi (Linford) Snyder & Hansen defence responses increased only slightly and transiently, if at all.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.