Enhanced resistance to sheath blight by constitutive expression of infection-related rice chitinase in transgenic elite indica rice cultivars

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.

/pdf/differential-expression-of-eight-chitinase-genes-in-medicago-2r4whucp9y.pdf

Differential expression of eight chitinase genes in Medicago truncatula roots during mycorrhiza formation, nodulation, and pathogen infection.

Pathogenesis-related proteins (PR-proteins) are induced in plants in response to attack by microbial or insect pests. They have been classified into several groups (PR-1 through PR-14 at present) based on their amino acid sequences and biochemical functions. Many of these proteins that have been purified from infected plants or seed extracts possess antifungal or insecticidal activity. Genes and cDNA clones for all classes of PR-proteins have been isolated from a variety of cereals. Some of these genes/cDNAs have been used to transform cereals. This review presents a summary of the PR-proteins and their genes characterized from rice, wheat, barley, sorghum and maize. Efforts to improve disease or insect resistance of these cereal plants by genetic engineering using genes for PR-proteins also are discussed. In many cases, the expression of the PR-proteins either singly or in combination appears to improve resistance to fungi or insects. In addition, chromosomal location of the PR-protein genes indicates that members of the same family of PR-protein genes or sometimes even several families of PR-protein genes often are clustered in the cereal genome, suggesting coordinate regulation. Some of these PR-protein genes map closely to quantitative traits loci. Some concerns regarding the use of genes encoding PR-proteins for genetic modification of cereals also are addressed.

https://www.k-state.edu/wgrc/Publications/2001/6936.pdf

Pathogenesis-related proteins and their genes in cereals

The possible role of the octadecanoid signaling pathway with jasmonic acid (JA) as the central component in defense-gene regulation of pathogen-attacked rice was studied. Rice (Oryza sativa L.) seedlings were treated with JA or inoculated with the rice blast fungus Magnaporthe grisea (Hebert) Barr., and gene-expression patterns were compared between the two treatments. JA application induced the accumulation of a number of pathogenesis-related (PR) gene products at the mRNA and protein levels, but pathogen attack did not enhance the levels of (-)-JA during the time required for PR gene expression. Pathogen-induced accumulation of PR1-like proteins was reduced in plants treated with tetcyclacis, a novel inhibitor of jasmonate biosynthesis. There was an additive and negative interaction between JA and an elicitor from M. grisea with respect to induction of PR1-like proteins and of an abundant JA-and wound-induced protein of 26 kD, respectively. Finally, activation of the octadecanoid signaling pathway and induction of a number of PR genes by exogenous application of JA did not confer local acquired resistance to rice. The data suggest that accumulation of nonconjugated (-)-JA is not necessary for induction of PR genes and that JA does not orchestrate localized defense responses in pathogen-attacked rice. Instead, JA appears to be embedded in a signaling network with another pathogen-induced pathway(s) and may be required at a certain minimal level for induction of some PR genes.

http://www.plantphysiol.org/content/plantphysiol/114/1/79.full.pdf

Jasmonate-Inducible Genes Are Activated in Rice by Pathogen Attack without a Concomitant Increase in Endogenous Jasmonic Acid Levels.

Inoculation of bean hypocotyls with a nonpathogenic binucleate Rhizoctonia (BNR) species induced systemic resistance and protection of the roots and cotyledons to later challenge with the root rot pathogen Rhizoctonia solani or the anthracnose pathogen Colletotrichum lindemuthianum. Bean seedlings that were treated with BNR 48 h prior to their challenge with R. solani or C. lindemuthianum had few necrotic lesions and reduced disease severity as compared with seedlings not treated with BNR. Treatment with BNR 48 h prior to their challenge also elicited a significant and systemic increase in all cellular fractions of peroxidases, 1,3-beta-glucanases, and chitinases compared with the diseased and control plants. Compared with control plants, total peroxidases and glucanases increased twofold and eightfold, respectively, in all protected bean tissues. BNR 232-CG could not be recovered from the challenged hypocotyls or cotyledons, indicating that there was no contact between the inducer and the pathogen. Both the 1,3-beta-glucanases and the peroxidases were positively correlated with induced resistance.

Systemic Induction of Peroxidases, 1,3-beta-Glucanases, Chitinases, and Resistance in Bean Plants by Binucleate Rhizoctonia Species.

Extracts from several rice cultivars (Oryza saliva L. cvs IR58, 74586 and SC33) infected with the sheath blight pathogen Rhizoctonia solani, were analyzed to determine the isozyme distribution of chitinases (EC 3.2.1.14) and β-1,3-glucanases (EC 3.2.1.39). Upon infection by the fungal pathogen, two chitinases of 28 and 35 kDa and two β-1,3-glucanases of 30 and 32 kDa were shown to be induced in all cultivars. They resolved into multiple isozymes under nondenaturing electrophoretic conditions. Wounding, but not bacterial infection, resulted in the induction of these hydrolytic enzymes. Even though fungal infection resulted in induction of chitinases and β-glucanases in all cultivars, some cultivars that were moderately resistant to R. solani appeared to have higher levels of specific isozymes. A chitinase cDNA clone was identified by screening a library, prepared from RNA isolated from R. solani-infected rice plants, with an antibody to a bean chitinase. This cDNA encoded a 35-kDa chitinase which was significantly different in amino acid sequence from other rice chitinases described so far. Northern blot analysis of RNA from infected rice plants indicated that transcripts corresponding to this chitinase gene were induced upon fungal infection.

Kunwei Chen Cole

Papers

Induction of chitinases and β‐l,3‐glucanases in Rhizoctonia solani‐infected rice plants: Isolation of an infection‐related chitinase cDNA clone