Localized versus systemic effect of arbuscular mycorrhizal fungi on defence responses to Phytophthora infection in tomato plants

Abstract

Development of biological control for plant diseases is accepted as a durable and environmentally friendly alternative for agrochemicals. Arbuscular mycorrhizal fungi (AMF), which form symbiotic associations with root systems of most agricultural, horticultural and hardwood crop species, have been suggested as widespread potential bioprotective agents. In the present study the ability of two AMF (Glomus mosseae and Glomus intraradices) to induce local or systemic resistance to Phytophthora parasitica in tomato roots have been compared using a split root experimental system. Glomus mosseae was effective in reducing disease symptoms produced by P. parasitica infection, and evidence points to a combination of local and systemic mechanisms being responsible for this bioprotector effect. The biochemical analysis of different plant defence-related enzymes showed a local induction of mycorrhiza-related new isoforms of the hydrolytic enzymes chitinase, chitosanase and beta-1,3-glucanase, as well as superoxide dismutase, an enzyme which is involved in cell protection against oxidative stress. Systemic alterations of the activity of some of the constitutive isoforms were also observed in non-mycorrhizal roots of mycorrhizal plants. Studies on the lytic activity against Phytophthora cell wall of root protein extracts also corroborated a systemic effect of mycorrhizal symbiosis on tomato resistance to Phytophthora.

Defense Related Phytohormones Regulation in Arbuscular Mycorrhizal Symbioses Depends on the Partner Genotypes

“…It is possible that the different impact of each AMF on host defense signalling partially explains the functional diversity observed in terms of plant induced stress resistance. For example, it is tempting to speculate that the stronger activation by F. mosseae of JA signalling may underlie the higher ability of this AMF to induce mycorrhiza induced resistance (Jung et al 2012;Pozo et al 2002). Our results provide an overview of the changes related to stress related hormones in a well established mycorrhizal symbiosis, confirming our hypothesis that the changes depend on the partners genotypes and more specifically on the colonizing fungus.…”

“…Although AMF are considered non specific with respect to host range, there is evidence for certain "functional diversity". That is, both the plant and fungal genotypes determine the benefits of the interaction, some combinations being more efficient than others in terms of nutrition and/or stress resistance improvement (Cavagnaro et al 2001;Feddermann et al 2010;Pozo et al 2002;Smith et al 2004). The interaction requires a high degree of coordination between both partners, and bidirectional (plant and fungal) control assure a fair trade of resources between the symbionts (Kiers et al 2011).…”

Plant immune responses triggered by beneficial microbes

“…For instance, colonization of tomato roots by mycorrhizal fungi systemically provided protection against Phytophthora parasitica infection without direct accumulation of PR proteins. However, upon pathogen attack, mycorrhized plants significantly accumulated more PR proteins than nonmycorrhized plants [53]. Although JA emerged as an important regulator of mycorrhization [54], it remains to be elucidated whether JA serves as the endogenous signal in the mycorrhizainduced primed state.…”

Cloning and characterisation of a maize carotenoid cleavage dioxygenase (ZmCCD1) and its involvement in the biosynthesis of apocarotenoids with various roles in mutualistic and parasitic interactions

“…This protection has been suggested to be due to improved nutritional status of the host but there is ample evidence that this cannot be the (only) explanation (Johansson et al 2004;Harrison 2005). Several studies have shown that during mycorrhizal symbiosis defence-related genes are induced (Pozo et al 2002;Kuster et al 2004). Increased defence gene expression could possibly also explain why sorghum and maize that are colonised by AM fungi are infected to a lesser extent by Striga as defence gene expression could play a role in Striga resistance (Gowda et al 1999).…”