Local early induced resistance of plants as the first line of defence against bacteria

Abstract

This paper is an overview of a non-specific local early induced resistance (EIR) mechanism, distinct from the incompatible-specific hypersensitive reaction (HR). We have shown that the local induced resistance (LIR) described earlier is not a single and uniform response to pathogen infection, because an early (EIR) and a late form can be distinguished. EIR operates from 3-6 h post-inoculation (hpi) until about 20 hpi, and is inhibited by a short heat-shock or the eukaryotic protein synthesis inhibitor, cycloheximide. In contrast, LIR, which corresponds to the induced resistance forms discovered earlier, requires more time (about 24 h) and intensive illumination to develop, and is effective for a longer period. EIR develops parallel with HR and is sometimes able to prevent it when the induction time of HR is longer than the time required for the development of EIR. It seems that EIR inhibits the metabolism of bacteria and the activity of hrp genes which otherwise are required for the induction of HR. In a compatible host-pathogen relationship the effect of EIR fails to take place. The rapid development of EIR is greatly influenced by temperature and the physiological state of the plant. EIR activates the accumulation of hydrogen peroxide at the bacterial attachment, expressing new peroxidase isoenzymes in the initiated plant tissue. It seems that this is a native general local defence mechanism which can localise foreign organisms even at the penetration site.

Plant Immunity Directly or Indirectly Restricts the Injection of Type III Effectors by the Pseudomonas syringae Type III Secretion System

“…This a reasonably quick response relative to the 12 to 24 h generally required for production of an HR. However, PTI-induced inhibition of the HR appears to require de novo transcription and translation as it was previously reported that the protein synthesis inhibitor cycloheximide restores the HR (Klement et al, 2003). Interestingly, HR inhibition induced by flg21 lasted through 2 d, while HR inhibition induced by intact bacteria persisted over a 2-week period.…”

“…The PTI-induced inhibition of the HR has previously only been reported in the solanaceous plants tobacco, N. benthamiana, and pepper (Capsicum annuum; Newman et al, 2000;Klement et al, 2003;Oh and Collmer, 2005). PTI-induced inhibition of the HR can also be recapitulated in Arabidopsis leaves (Supplemental Fig.…”

“…To explore the mechanism underlying PTI inhibition of the HR (Newman et al, 2000;Klement et al, 2003;Oh and Collmer, 2005), we first needed to define the conditions necessary for it to occur in our system. To cause PTI, we used two well-established PTI inducers: one was the nonpathogenic bacterial strain P. fluorescens(pLN1965) (Hauck et al, 2003;Guo et al, 2009), and the other was a 21-amino-acid peptide (flg21) from the N terminus of flagellin (Felix et al, 1999).…”

“…One PTI suppression assay using P. fluorescens (pLN18) employed by Oh and Collmer (2005) took advantage of earlier observations indicating that PTI could inhibit the ability of the plant to mount an HR in response to an ETI-inducing bacterial strain (Newman et al, 2000;Klement et al, 2003). In this assay, the PTI inducers P. fluorescens(pLN18) or a 22-amino-acid peptide from flagellin (flg22) are infiltrated into Nicotiana benthamiana.…”

Transcriptome analysis of a bacterially induced basal and hypersensitive response of Medicago truncatula

“…In addition to the HR, there is a more general plant defense response that also recognizes saprophytic bacteria and bacteria without functional TTSS and subsequently inhibits their multiplication (Klement et al , 2003. There are many synonyms in the literature for this general recognition and defense system, such as basic, basal, general resistance.…”