ROS Signaling Mediates Directional Cell Elongation and Somatic Cell Fusion in the Red Alga Griffithsia monilis

Abstract

In many filamentous red algae, cells that die from physical damage are replaced through somatic fusion of repair cells formed from adjacent cells. We visualized ROS generation in repair cells of Giriffthsia monilis using DCFH-DA staining and examined the expression of the genes involved in wound healing using quantitative PCR. Repair cells elongate along the H2O2 gradient, meet at each other’s tips where the H2O2 concentration is highest, and undergo somatic fusion. No wound response occurred with ascorbic acid treatment. Conversely, H2O2 treatment induced many repair cells, leading to multiple somatic cell fusions. Diphenylene iodonium (DPI) or caffeine treatment reversibly inhibited ROS production in repair cells and blocked the progression of the wound response suggesting that ROS and calcium signaling are involved in the process. Four G. monilis homologues of NADPH-oxidase (GmRBOHs) were identified. The expression of GmRBOHs was upregulated upon injury, peaking 1 h post injury, and decreasing to initial levels when repair cells began to elongate. Our results suggest that ROS generated upon cell injury activates Ca2+ channels and upregulates the expression of GmRBOHs, and that H2O2 generated from repair cells mediates induced repair cell elongation leading to somatic cell fusion and filament repair.

Oomycete pathogens, red algal defense mechanisms and control measures

“…Calcium-mediated ROS signaling mediates the fertilization and wound-healing responses of red algae and also plays an important role in response to pathogens (Weinberger et al 2005, Moon et al 2022, Shim et al 2022. NADPH oxidase in the cell membrane (called respiratory burst oxidase homolog or RBOH) reduces oxygen to superoxide, which rapidly forms hydrogen peroxide and diffuses from cell to cell through the extracellular space (Torres et al 2006, Perez and Brown 2014, Peláez-Vico et al 2022.…”

Synchronous nuclear division and the role of the cytoskeleton in the multinucleate red alga <italic>Griffithsia monilis</italic>

“…All nuclei in the same cytoplasm respond in a similar way to an environmental stimulus, but for a stimulus localized to a small part of a large cell, such as a G. monilis cell, it is a very interesting question whether all or only some of the nuclei in the cell will transcribe responsive genes. The wound-healing process in G. monilis provides a clue to this question (Moon et al 2022). When a cell dies in the G. monilis filament, neighboring cells produce repair cells, and during the process of wound healing by somatic fusion between them, the repair cells produce reactive oxygen species (ROS) only on the facing sides (Moon et al 2022).…”

“…Actin has been shown to mediate the movement of spermatial nuclei within the trichogynes of several red algae during fertilization (Kim and Kim 1999, Wilson et al 2002, Shim et al 2021). However, investigations on the involvement of microtubules in various cellular responses in red algae have only recently begun (Moon et al 2022).…”

Red macroalgae in the genomic era

“…The movement of spermatia is mediated by actin microfilaments that wrap around the male nucleus as it is transported down the trichogyne, which eventually degenerate after karyogamy has taken place (Shim et al ., 2020). The interplay between reactive oxygen species (ROS) and Ca 2+ signalling also plays a role in communication between the spermatium and trichogyne (Shim et al ., 2022), which might be a common signalling mechanism in other red algal developmental processes (Moon et al ., 2022). Once the spermatium is attached, ROS diffuses across the cell membranes in the form of H 2 O 2 and triggers more ROS production in the carpogonium and associated cells (Shim et al ., 2022).…”