Plant basal resistance - Universiteit Utrecht

Chapter 1
(PRRs; Gomez-Gomez and Boller, 2000; Scheer and Ryan, 2002; Huffaker et al., 2006; Miya
et al., 2007). Although immune response triggered by these defence elicitors are commonly
referred to as PAMP-triggered immunity (PTI), the term ‘pattern-triggered immunity’ would
be more appropriate as it more collectively reflects responses to PAMPs, MAMPs, DAMPs
and HAMPs. The PTI response is associated with a wide range of quickly activated defence
mechanisms, such as localized callose deposition, reactive oxygen species accumulation and
single cell death responses (Schwessinger and Zipfel, 2008).
Figure 1: Induced plant defence is a multi-layered phenomenon involving a multitude of defence
mechanisms that are activated at different stages of the plant-microbe interaction. Upon first
contact with a microbial pathogen, plants can express pre-invasive defence mechanisms. A wellknown
example is the rapid closure of stomata upon recognition of pathogen-associated molecular
patterns (PAMPs). When the invading pathogen is capable of penetrating into the host tissue, it faces
a second layer of inducible plant defences. This relatively early post-invasive defence is marked by
accumulation of reactive oxygen species (ROS), often directly followed by deposition of callose-rich
papillae. If the attacking pathogen is able to suppress and/or evade this early post-invasive defence
barrier, it will encounter a third layer of inducible defences. This relatively late post-invasive defence is
associated with the activation a wide range of defence mechanisms that are under control by de novo
produced signalling hormones, such as salicylic acid. Late post-invasive defence is also associated with
the generation of vascular long-distance signals that can prime systemic plant parts against upcoming
pathogen attack. Red cells indicate defence-expressing cells and orange cells indicate those that are
being successfully parasitized. The figure is adopted from Ton et al. (2009).
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