Plants are sessile organisms that are under constant attack from microbes. They rely on both preformed defenses, and their innate immune system to ward of the microbial pathogens. Preformed defences include for example the cell wall and cuticle, which act as physical barriers to microbial colonization. The plant immune system is composed of surveillance systems that perceive several general microbe elicitors, which allow plants to switch from growth and development into a defense mode, rejecting most potentially harmful microbes. The elicitors are essential structures for pathogen survival and are conserved among pathogens. The conserved microbe-specific molecules, referred to as microbe- or
pathogen-associated molecular patterns (MAMPs or
PAMPs), are recognized by the plant innate immune systems
pattern recognition receptors (
PRRs). General elicitors like
flagellin (Flg),
elongation factor Tu (
EF-Tu),
peptidoglycan (PGN),
lipopolysaccharides (LPS), Ax21 (Activator of XA21-mediated immunity in rice), fungal
chitin, and β-
glucans from oomycetes are recognized by plant surface localized
PRRs. Several of the MAMPs and their corresponding
PRRs have, in recent years, been identified. This review focuses on the current knowledge regarding important MAMPs from bacteria, fungi, and oomycetes, their structure, the plant
PRRs that recognizes them, and how they induce MAMP-triggered immunity (MTI) in plants.