Plant innate immune response

Antimicrobial peptides have also been postulated to play a central role in the plant innate immune response to microbial infection and include the thionins, the defensins, and the cyclotides. It has been demonstrated that physiological concentrations of the thionins are active against bacteria and fungi in vitro and the heterologous expression of thionins in a transgenic plant model confer protection against bacterial challenge. ... 

Thus, together these studies suggest that the oxidative burst machinery has evolved before the crown diversification of eukaryotes (Baldauf 2003) to provide marine algal lineages with natural and induced innate immunity mechanisms. These play a role similar to the HR in terrestrial plants infected by incompatible pathogens and they share important common traits with the innate immunity response of mammalian phagocytes. 

The MAPK cascade in the plant s defense against bacterial pathogens is remarkably similar to the innate immune response triggered by bacterial lipopolysac-charide and mediated by the Toll-like receptors in mammals (Fig. 12-30b). Other membrane receptors use similar mechanisms to activate a MAPK cascade, ultimately activating transcription factors and turning on the genes essential to the defense response. 

In addition to the plant defensins mentioned in Section 4, defensins are also widespread in vertebrates. These antimicrobial peptides are involved in the innate immune response, and are classified into three subfamilies that present... 

In this chapter, we will review the current knowledge of the role of LPS as a M AMP in plant innate immunity. We will give an overview of the range of responses induced by LPS, the sub-structures within LPS that are recognized by plants and variations within the LPS structure that can alter its activity as a MAMP. We will go on to discuss new work that suggests a role for the plasma-membrane resident syntaxin PEN1 in transduction of the LPS signal. 

Structural analysis of LOS from a mutant of Xcc defective in core completion revealed that this mutant had modifications in the lipid A moiety, which had reduced acylation and was further derivatised with phosphoryl ethanolamine residues (Dow et al., 1995 Silipo et al., 2008). These changes in lipid A structure abolished the ability to trigger innate immune responses in Arabidopsis (Silipo et al., 2008). Importantly these findings indicate that Xcc has the capacity to modify the structure of its lipid A to reduce its activity as a MAMP in plants (Silipo et al., 2008). It is not known whether these (or other) modifications to lipid A occur when bacteria are within plants. 

The innate immune system is found across all organisms and is thought to have originated before the split into animal and plant kingdoms. It is the body s primaiy response to attack. Receptors used in this system must be capable of recognising abroad range of pathogens. This... 

Animals and plants constantly interact with bacteria present within their environment. For an infection to develop, such microorganisms must remain associated with the host and increase their numbers more rapidly than they can either be eliminated or killed. This balance relates to the ability of the bacterium to mobilize nutrients and multiply in the face of innate defences and a developing immune response by the now compromised host. 

The functional oligosaccharides of various origins (viruses, bacteria, plants and fungi) have been shown to exert potent immunomodulatory activities [164, 194, 208, 210]. The functional oligosaccharides also improve immunity which innate defense responses activated through the interaction of sugar moieties with innate receptors on the plasma membrane... 

---