Unraveling rhizobacteria- and abscisic acid-induced pathogen resistance in rice (Oryza sativa L.)
Year: 2008
Type: dissertation
Abstract: Induced disease resistance is the phenomenon by which plants exhibit a heightened level of resistance against pathogen infection after appropriate stimulation. In contrast to the relative wealth of information on inducible resistance responses in dicotyledoneous plants, our current understanding of the molecular machinery governing induced resistance in monocotyledoneous crops is still in its infancy. In light of aforementioned knowledge gap, this dissertation aimed to expand our knowledge on the mechanistic basis of biologically and chemically induced resistance in rice, the world’s most important staple food and a central model for cereal crops. The first part of this work is dedicated to the phenomenon of rhizobacteria-induced systemic resistance (ISR). Using an extensive set of bacterial mutants, we pinpoint the phenazine pigment pyocyanin as a two-faced ISR elicitor capable of inducing resistance against the blast pathogen Magnaporthe oryzae, while promoting susceptibility to the sheath blight pathogen Rhizoctonia solani. In addition, evidence is brought forward demonstrating that the ambivalent role of pyocyanin in Pseudomonas aeruginosa 7NSK2-mediated ISR is due to its ability to modulate the plant’s oxidative machinery. Aiming to further dissect the rhizobacteria-mediated ISR response, we continued exploring the bacterial traits and host immune responses underpinning ISR elicited by the P. fluorescens strain WCS374r. The cumulative results favor a model whereby WCS374r bacteria trigger ISR against M. oryzae via secretion of a pseudobactin-type siderophore, thereby sensitizing naïve leaves for potentiated expression of a salicylic acid-repressible, yet jasmonate/ethylene-dependent multifaceted defence response. The differences and similarities between WCS374r-ISR and blast resistance triggered by the salicylic acid mimic benzothiadiazole are addressed as well. In the second part of this work, attention was shifted to the role of the phytohormone abscisic acid (ABA) in modulating rice pathogen defence. We show that topical application of ABA enhances basal resistance against the brown spot-causing ascomycete Cochliobolus miyabeanus. Pursuing a multidisciplinary approach, evidence is provided supporting ABA-mediated repression of pathogen-induced ethylene signalling as a core resistance mechanism. In addition, we present a novel role for the MAPK OsMPK5 as a critical modulator of this ABA/ET crosstalk, and describe how ABA interferes with the postulated fungal manipulation of the plant.
Author: David De Vleesschauwer
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2315763738