These vesicles allow effectors to enter the attached cells.
Hypothesis on the origin of viruses:
Primordial cells produced intracellular contents that released vesicles.
One vesicle contained content that could reproduce in other cells.
Effectors also referred to as virulence factors.
Effectors can be parts of the cell wall or flagella that elicit physiological responses in plants.
These effectors are released to facilitate infection and manipulation of host cells.
Motility and Infection Mechanics
Campus movement:
Some pathogens demonstrate twitching motility.
They can move against the flow in xylem vessels.
Attachment and movement:
Pathogens attach to vessel walls and move downward or laterally.
Almost all plant cells have channels to share contents; pathogens can hijack these channels.
Flow limitations in xylem:
Pathogens are confined to movement within xylem tissues.
Genetic manipulation studies:
Knockout experiments are done to identify which genes influence twitching motility in bacteria.
Wild type (WT) is the naturally moving bacteria; gene knockouts can increase or eliminate movement.
Testing Movement and Environmental Signals
Microscopic flow dynamics:
Micro microscope slides with channels create artificial flow to study movement.
Chemical signals dictate movement:
Bacteria move toward nutrients and away from harmful substances.
Biofilm formation:
Bacteria clump together, leading to xylem blockage and symptoms like leaf scorch and wilting.
Pathogen Transmission by Vectors
Vector species:
Blue-green sharpshooter and glassy-winged sharpshooter; both facilitate bacterial movement without being harmed.
Complex relationships in nature:
Example: "Zombie fungi" that change behavior in ants for their reproduction.
Certain bacteria may influence insect behavior and reproduction.
Signs of infection:
Sparse areas in fields indicate pathogen entry and spread, leading to stunted growth.
Biotic diseases manifest unevenly in fields; controlling the movement of insects helps manage diseases.
Disease Management Strategies
No definitive cure for these diseases.
Main control methods include managing insect vectors and developing resistant plant varieties.
Systemic insecticides like imidacloprid are absorbed by plants and transported through their vascular systems but are controversial due to effects on beneficial insects, particularly bees.
Resistance breeding and GMO introduction are additional management strategies.
Olive Quick Decline Syndrome and Spread Analysis
Caused by the same pathogens affecting xylem-feeding insects.
Symptoms include dieback of branches leading to tree death, particularly prominent in olive cultivation in Italy since 2013.
The geographical spread of the disease and public skepticism about scientific findings highlight tensions between agriculture and community trust.
Agrobacterium Tumefaciens
Causes crown gall tumors on plants through hyperplasia and hypertrophy.
Mechanism of action:
Attaches to host plants through wounds and releases virulence genes, which are activated by plant metabolites.
Inserts DNA from the T-region of a plasmid into the plant's nucleus, stimulating overproduction of growth hormones (cytokinins and auxins).
The result leads to uncontrolled cell division, creating more nutrients for the bacteria, influencing plant tissue to produce opines as a food source.
Biotechnology Application of Agrobacterium
The method involves modifying the plasmid to introduce desired traits into plants, making it a tool for genetic engineering and GMO development.
The process includes preparing plant cells (e.g., protoplasts) and using type four secretion systems to facilitate DNA transfer.
Ralstonia Solanacearum
Overview:
Soil-borne pathogen that affects over 250 plant species.
Causes potato brown rot, difficult to manage due to its ability to survive in soil for up to four years.
Notably classified as a bioterrorism agent due to its severe implications for food security.
Symptoms of infection:
Significant wilting during the day, recovery at night; cutting the stem reveals brown vascular tissue and milky exudate, indicating infection severity.
Management challenges:
Difficult to control due to persistence in soil, necessitating resistant rootstocks, grafting strategies, and crop rotation.