Defence at dawn

摘要

Plants cannot avoid pathogens by fleeing, so they have evolved mechanisms to resist attack. Those mechanisms include forms of immunity, and on page 110 of this issue Wang et al. reveal an unexpected connection between plant immunity and the circadian clock. Plant immunity is controlled by a complex and incompletely understood signalling net- work. The first level of defence consists of the recognition of mol-ecules called pathogen-associated molecular patterns (PAMPs) and the subsequent initiation of PAMP-triggered immunity2. Because many pathogens can suppress this response, often by means of proteins generically termed effec-tors, plants have evolved disease-resistance (R) genes that recognize effectors or the action of effectors on their host-cell targets. The consequent effector-triggered immunity involves the repro-gramming of gene transcription, which culminates in physiological changes that include the hypersen-sitive (cell death) response.