Chitosan activates a MAP-kinase pathway and modifies abundance of defense-related transcripts in calli of Cocos nucifera L.

As the study of coconut defense responses against pathogenic microorganisms is hampered by the absence of suitable model systems, we investigated if imbibition of coconut calli with chitosan could be used in vitro to simulate the molecular interactions that occur with pathogens. Our results showed that calli imbibition with 10 mg mL−1 chitosan caused the accumulation of hydrogen peroxide, and stimulated a β-1,3-glucanase activity with an Rf near 0.1. In addition, in-gel kinase assay and specific immunoblotting showed that a ∼46 kDa MAPK-like protein was activated shortly after elicitation, and remained in this state for at least 80 min. Chitosan addition also differentially modified the expression of some genes, whose DNA sequence showed high similarities to receptor-like kinases (RLKs), Verticillium-like protein, and mitochondrial alternate oxidase 1b. Addition of salicylic acid to the calli also modified transcript abundance for these genes, while methyl jasmonate did not seem to influence their expression, implying that they could be involved in defense responses. These results strongly suggest that elicitation of coconut tissues cultivated in vitro constitutes a suitable alternative to characterize both biochemical and molecular interactions that occur between the coconut palm and its associated pathogens.