Isolation and characterization of novel cDNA clones of acidic chitinases and β-1,3-glucanases from wheat spikes infected by Fusarium graminearum

Chitinases and beta -1,3-glucanases are important components of plant defense in response to attack by pathogens. To identify specific chitinases and beta -1,3-glucanases, we constructed a cDNA library using mRNA from wheat spikelets inoculated with conidia of Fusarium graminearum. Two chitinase and two beta -1,3-glucanase clones were isolated using a rice chitinase Ia gene and barley cDNA clones for chitinase II and beta -1,3-glucanase as probes. Sequence analysis showed that the cDNA clone SM194 encodes an acidic isoform of class-VII chitinase, the cDNA clone SM383 encodes a class-IV chitinase and the cDNA clones SM289 and SM638 encode two different acidic isoforms of beta -1,3-glucanases. Nulli-tetrasomic analysis indicated that SM194 and SM383 were located on all of the group-2 chromosomes of wheat. Genetic mapping showed that at least three copies of class-IV and/or class-VII chitinase genes were clustered on the long arm of chromosome 2D of Aegilops tauschii and that they mapped genetically close to the centromere. SM289 and SM638 were located on all of the group 3 chromosomes of wheat by nulli-tetrasomic analysis, and to the beta -1,3-glucanase clusters in the 3BL and 3DL chromosome arms of wheat by genetic mapping. Northern blot hybridization showed that the expression of these genes is induced upon infection with Fusarium graminearum. The accumulation of transcripts for these PR-proteins was more rapid in the resistant variety Sumai 3 than in its susceptible mutant during the first 24 h. This is the first report of the induction of class-IV and class-VII chitinases in cereals by a fungal pathogen.