Microbial Interactions and Plant Pathogenesis

Microbial Interactions in Plant Pathogenesis

• Invasive pathogens can establish mutualistic relationships with native microbes, negatively impacting plant health and accelerating disease progression.
• These relationships are hidden within complex interactions between different microbial species.
• Intra-species communication (e.g., quorum sensing) is crucial for microbial behaviors.
  • Quorum sensing allows bacteria to sense population density and regulate activities like motility, biofilm formation, and virulence.
  • Fungi also exhibit similar quorum regulation for behaviors like germination, colony formation, and sporulation.
• Inter-species communication (e.g., quorum quenching) exists.
  • Symbiotic bacteria can interfere with pathogens' quorum-sensing mechanisms.
  • Examples include Microbacterium testaceum interfering with Pectobacterium carotovorum.
• Mutualistic relationships exist within microbial communities, benefiting all involved.
  • Gut microbiota provides nutrients (carbon and nitrogen) to invasive pathogens, boosting their growth and virulence.
  • Beneficial bacteria can be manipulated into pathogens by picking up virulence factors.
• Microbial Cooperation extends to different kingdoms (bacteria and fungi).
  • Physical and chemical interactions between bacteria and fungi influence plant pathogens.
  • Bacteria may use fungi as vectors to spread infection.
  • Fungi might utilize bacteria to enhance infection and disease progression, including building protection through biofilms (physical barrier)

Chemical Interactions

• Chemical signaling is prevalent in microbial interactions.
  • Bacteria and fungi use small molecules like volatile organic compounds (VOCs) to signal and affect each other's behavior.
  • Release of VOCs by fungi can change bacterial motility and potentially facilitate co-infections.
  • Fungi like Verticillium dahliae can produce effectors to counter beneficial bacteria while enabling their own colonization of host plants.
• Effectors are large proteins involved in interkingdom interactions.
  • Pathogens use secretion systems to deliver effectors that manipulate plant immune responses.
  • Examples of these effectors include those that manipulate entry, nutrient acquisition, defense suppression, and protein translocation.

Plant Responses and Pathobiome Management

• Plants recognize microbial molecules (MAMPs/PAMPs) using pattern recognition receptors (PRRs), triggering innate immunity.
  • Key MAMP/PAMPs include lipopolysaccharides, flagellin, and chitin.
• Two Plant Innate immunity levels (PTI and ETI) can be used.
• Pathobiome members can counter plant defenses via effectors that evade recognition by plant resistance (R) proteins, leading to effector-triggered susceptibility (ETS).
• Plants and pathogens can adapt and evolve in response to each other's actions.
• Conventional treatments focusing on one pathogen are less effective as pathogens might utilize multiple molecules for virulence.
• Understanding the complex cooperation within the pathobiome is crucial for creating effective anti-disease strategies.

Multiscale Interactions

• Pathobiome interactions occur at multiple levels (plant-microbe, microbe-insect, multitrophic).
  • Plants use symbiotic microbes to defend against pathogens, while pathogens counter this alliance.
• Dysbiotic symptoms in plants (ex: leaf necrosis, chlorosis), and community shifts in microbial composition may indicate pathobiome involvement.
• The mechanisms behind these shifts are linked to plant immunity pathways (e.g., PAMP and ETI).
• Plant immunity deficiencies and pathway disruptions can result in shifts favoring pathogenic microbial communities.