Secondary metabolites in plant innate immunity: conserved function of divergent chemicals

Abstract

948I.948II.949III.953IV.956V.958VI.960960References960 Summary Plant secondary metabolites carry out numerous functions in interactions between plants and a broad range of other organisms. Experimental evidence strongly supports the indispensable contribution of many constitutive and pathogen‐inducible phytochemicals to plant innate immunity. Extensive studies on model plant species, particularly Arabidopsis thaliana, have brought significant advances in our understanding of the molecular mechanisms underpinning pathogen‐triggered biosynthesis and activation of defensive secondary metabolites. However, despite the proven significance of secondary metabolites in plant response to pathogenic microorganisms, little is known about the precise mechanisms underlying their contribution to plant immunity. This insufficiency concerns information on the dynamics of cellular and subcellular localization of defensive phytochemicals during the encounters with microbial pathogens and precise knowledge on their mode of action. As many secondary metabolites are characterized by their in vitro antimicrobial activity, these compounds were commonly considered to function in plant defense as in planta antibiotics. Strikingly, recent experimental evidence suggests that at least some of these compounds alternatively may be involved in controlling several immune responses that are evolutionarily conserved in the plant kingdom, including callose deposition and programmed cell death.

Plant Innate Immune Response: Qualitative and Quantitative Resistance

“…Plants produce thousands of phenols, flavonoids, terpenes, fatty acids, and alkaloids that are antimicrobial. Resistance metabolites may also be biosynthesized de novo following pathogen invasion; these are commonly known as phytoalexins (RRI) ( Table 1) (Ahuja et al, 2012;Pedras and To, 2015;Piasecka et al, 2015). Resistance depends not only on the amount of metabolite biosynthesized by the plant, but also on the antimicrobial property of a given metabolite (Piasecka et al, 2015).…”

“…Resistance metabolites may also be biosynthesized de novo following pathogen invasion; these are commonly known as phytoalexins (RRI) ( Table 1) (Ahuja et al, 2012;Pedras and To, 2015;Piasecka et al, 2015). Resistance depends not only on the amount of metabolite biosynthesized by the plant, but also on the antimicrobial property of a given metabolite (Piasecka et al, 2015). These phytoalexins, in hundreds, are biosynthesized by R RRM genes in various specific metabolic pathways (Figure 2) (Ahuja et al, 2012).…”

Metabolomics of Disease Resistance in Crops

“…The synthesis and accumulation of these compounds is induced after perception of pathogen attack (perception of PAMPs or pathogen effector molecules). Defense compounds can be divided into phytoalexins, that are produced upon pathogen perception, and phytoanticipins that are synthesized in an inactive form and pathogen recognition triggers its biochemical modification into a toxic derivative (Piasecka et al, 2015). It is important to recall that plants challenged with pathogenic fungal or bacterial strains modify their metabolome in the attacked cells (local response) and this response can be extended to the rest of the plant (systemic response).…”

“…These molecules are widely distributed in the plant kingdom (mainly in dicots but also in some monocots) (Huhman et al, 2005;Piasecka et al, 2015). This group includes triterpenoids from Avena spp.…”

“…This group includes triterpenoids from Avena spp. named avenacins (A1, A2, B1 and B2) only accumulated in roots whereas avenacosides, with steroidal sapogenins, are accumulated in leaves (Piasecka et al, 2015). In addition, steroidal glycoalkaloids found in solanaceous plant species constitute important representatives of this group (e.g.…”