Chitin Triggers Calcium-mediated Immune Response in the Plant Model Physcomitrella patens.

A characteristic feature of a plant immune response is the increase of the cytosolic calcium (Ca(2+)) concentration following infection, which results in the downstream activation of immune response regulators. The bryophyte Physcomitrella patens has been shown to mount an immune response when exposed to bacteria, fungi, or chitin elicitation, in a manner similar to the one observed in Arabidopsis thaliana. Nevertheless, whether P. patens' response to microorganisms exposure is Ca(2+) mediated is currently unknown. Here we show P. patens plants treated with chitin oligosaccharides exhibit Ca(2+) oscillations, and that a calcium ionophore can stimulate the expression of defense-related genes. Chitin oligosaccharide treatment also results in an inhibition of growth, which can be explained by the depolymerization of the apical actin cytoskeleton of tip growing cells. These results suggest that chitin triggered calcium oscillations are conserved and were likely present in the common ancestor of bryophytes and vascular plants.