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Characterization and Expression of β-1,3-Glucanase Genes in Jujube Fruit Induced by the Microbial Biocontrol Agent Cryptococcus laurentii

Two β-1,3-glucanase genes were cloned from jujube (Ziziphus jujuba Mill) fruit and designated Glu-1 and Glu-2 (GenBank accession numbers DQ012940 and DQ093571), respectively. The expression of Glu-1 and Glu-2 in jujube fruit in response to wounding and microbial biocontrol agent was evaluated by semi-quantitative reverse-transcription polymerase chain reaction analysis. Wounding and treatment with Cryptococcus laurentii stimulated an increase in β-1,3-glucanase (EC 3.2.1.39) activity in jujube fruit. Analysis of gene expression proved that Glu-1 was highly induced both by wounding and C. laurentii, whereas Glu-2 was broadly not responsive to the yeast. The expression of Glu-1 was noticeably enhanced with increased concentrations of C. laurentii, suggesting that Glu-1 may play a role in defense responses to fungal pathogens. The results hold true at the levels of gene activation and enzyme accumulation in jujube fruit treated by both stimuli, resulting in a significant decrease in disease incidence and lesion diameter, thus providing evidence that changes in β-1,3-glucanase activity are related to expression of the genes. Taken together, these findings suggest the possible use of β-1,3-glucanase activity as a biochemical marker for screening jujube fruit against fungal pathogens, and also provide a mechanistic framework for the functions of β-1,3-glucanase in defense responses.