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.