β-1,3-Glucanase (PR-2) differential gene expression during compatible and incompatible interactions between <em>Xanthomonas axonopodis </em>and <em>Citrus sinensis</em>

Abstract

The production of citrus fruits is one of the most important agro-industrial activities in Brazil, which has been constantly threatened by the citrus canker disease, caused by the Gram- negative bacterium Xanthomonas axonopodis pv. citri (Xac-A). In contact with host plants, Xac-A causes injuries to leaves, fruits, and stems. On the other hand, a necrotic reaction is induced when this pathogen infects a non-host plant. The induction of pathogenesis-related (PR) proteins is associated to the plant defense response to the pathogen attack. In this work we investigated the β-1,3-glucanase (PR-2) gene expression during X. axonopodis pv. aurantifolli C (Xaa-C)::Citrus interaction (non-host resistance response) and during Xac-A::citrus interaction (citrus canker disease). Bacterial suspensions (Xac-A or Xaa-C) were inoculated in orange leaves (Citrus sinensis), which were then collected at different time points during the infection process. The expression of the PR-2 coding gene has been analyzed by Northern blot using a citrus β-1,3-glucanase probe obtained by PCR using specific oligonucleotide and orange leaves genomic DNA. The Xaa-C::Citrus interaction has shown to induce a faster and more intense pr-2 gene expression when compared to Xac-A::Citrus interaction, suggesting a resistance role to citrus PR-2 protein expressed early during Xaa-C infection.

Additional keywords: citrus canker; nonhost resistance; Xanthomonas axonopodis pv.citri; plantpathogen interaction.