3.2 ROS as a direct interactor /regulator
ROS act as direct regulators of plasmodesmata by influencing their
permeability, often through mechanisms involving the modulation of
callose deposition, actin dynamics, and redox signaling. This regulation
is crucial for the coordinated transport of various molecules between
plant cells and is a key component of plant growth, development, and
stress responses.
Elevated ROS levels influence the
phosphorylation status of various proteins, including those associated
with plasmodesmata. Phosphorylation modifications can alter the
conformation and interactions of these proteins, affecting their ability
to regulate plasmodesmal permeability. For example, ROS application
intensifies the interaction between PD proteins (CML41) and NCRK
[described above; (Vu et al., 2022)]. ROS can also induce redox
modifications in proteins, forming disulfide bonds or other covalent
modifications. These changes can impact protein-protein interactions,
potentially altering the assembly and stability of plasmodesmal
structures (Cremers and Jakob, 2013; McDonagh, 2017; Juan et al., 2021).
ROS can modulate actin filament dynamics by activating actin-binding
proteins. Alterations in actin organization influence plasmodesmal
aperture and transport rates, potentially impacting the movement of
molecules through these channels. Actin remodeling is dependent on ROS
generated by the defense-associated NADPH oxidase, RBOHD. For example,
denser actin arrays were observed in response to pathogen- and
damage-associated patterns (PAMP and DAMP) than in mock-treated plants.
RBOHD mutant fails to induces in cortical actin arrays in response to
PAMP and DAMP (Li et al., 2017).
Lipid peroxidation is a process wherein oxidants, such as free radicals,
target lipids containing carbon-carbon double bonds, notably
polyunsaturated fatty acids (PUFAs) (Alche, 2019; Juan et al., 2021).
Plasma membranes and chloroplasts are particularly susceptible to ROS
generation due to their rich content of PUFAs. In PD, there is a higher
prevalence of and monounsaturated fatty acids (MUFAs), like
sphingolipids, which are essential components of PD, compared to PUFAs
(Grison et al., 2015; Zhang et al., 2022). While MUFAs are less
susceptible to lipid peroxidation than PUFAs, peroxidation of PUFA in
conditions of heightened oxidative stress disrupt lipid bilayer, and has
the potential to impact structural integrity and permeability.