The moss Physcomitrella patens is an evolutionarily basal model system suitable for the analysis of plant defence responses activated after pathogen assault. Upon
infection with the necrotroph Botrytis cinerea, several defence mechanisms are induced in P. patens, including the fortification of the plant cell wall by the incorporation of phenolic compounds and the induced expression of related genes. Botrytis cinerea
infection also activates the accumulation of
reactive oxygen species and cell death with hallmarks of programmed cell death in moss tissues.
Salicylic acid (SA) levels also increase after
fungal infection, and treatment with SA enhances transcript accumulation of the defence gene
phenylalanine ammonia-lyase (PAL) in P. patens colonies. The expression levels of the genes involved in
12-oxo-phytodienoic acid (
OPDA) synthesis, including
lipoxygenase (LOX) and
allene oxide synthase (AOS), increase in P. patens gametophytes after pathogen assault, together with a rise in free
linolenic acid and
OPDA concentrations. However,
jasmonic acid (JA) could not be detected in healthy or infected tissues of this plant. Our results suggest that, although conserved defence signals, such as SA and
OPDA, are synthesized and are probably involved in the defence response of P. patens against B. cinerea
infection, JA production appears to be missing. Interestingly, P. patens responds to
OPDA and
methyl jasmonate by reducing moss colony growth and rhizoid length, suggesting that
jasmonate perception is present in mosses. Thus, P. patens can provide clues with regard to the evolution of different defence pathways in plants, including signalling and perception of
OPDA and jasmonates in nonflowering and flowering plants.