Lipo-chitooligosaccharide signalling blocks a rapid pathogen-induced ROS burst without impeding immunity

Area of Science:

• Plant-microbe interactions
• Molecular plant pathology
• Plant symbiosis

Background:

• Microbial signals at plant surfaces dictate host immunity or symbiosis.
• Lipo-chitooligosaccharides (LCOs) from symbionts initiate symbiotic programs.
• Pathogen perception typically triggers reactive oxygen species (ROS) bursts and defense gene expression.

Purpose of the Study:

• Investigate the cross-talk between symbiotic and pathogenic signals in Medicago truncatula.
• Determine how LCO perception affects the plant's response to pathogen-associated molecular patterns.
• Elucidate the role of ROS in mediating plant responses to coincident microbial signals.

Main Methods:

• Incubation of Medicago truncatula seedlings with Aphanomyces euteiches culture filtrate (CF) and Sinorhizobium meliloti LCOs.
• Measurement of ROS release in response to microbial signals.
• Analysis of immunity-associated gene expression and disease resistance.

Main Results:

• Simultaneous or sequential application of CF and LCOs resulted in a strong ROS release.
• Pre-incubation with LCOs completely inhibited CF-induced ROS release.
• LCO treatment did not affect the expression of immunity-associated genes or disease resistance to A. euteiches.

Conclusions:

• Medicago truncatula evolved a ROS inhibition response to LCOs, facilitating symbiosis.
• This ROS inhibition allows for the establishment of symbiosis without compromising existing defense mechanisms.
• Plants can concurrently manage symbiotic and defense pathways through differential regulation of ROS.