Hydrogen peroxide signaling mediates fertilization and post-fertilization development in the red alga Bostrychia moritziana

<p><span><span><span>Reactive oxygen species (ROS) signaling has a multitude of roles in cellular processes throughout biology. We hypothesized that red algal fertilization may offer an interesting model to study ROS-mediated signaling as the stages of fertilization are complex and unique. </span></span></span><span><span><span>We microscopically localized ROS production and monitored the expression of three homologues of NADPH-oxidase in reproductive cells during fertilization. </span></span></span><span><span><span>ROSwere instantaneously produced by spermatia (sperm) when they attached to female trichogynes, diffused across the cell membrane in the form of H₂O₂, and triggered ROS generation in the carpogonium (egg) as well as carpogonial branch cells which are not in direct contact with spermatia. The expression of NADPH-oxidase homologues, <i>Bmrboh</i>s, began to be upregulated in the female plant upon gamete binding, peaking during the fertilization process and descending back to their original level after fertilization. Pretreatment with diphenylene iodonium (DPI) or caffeine blocked the gene expression as well as H₂O₂production. Post-fertilization development was also inhibited when the redox state of the plants were perturbed with H₂O₂ at any time before or after the fertilization. </span></span></span><span><span><span>Our results suggest that H₂O₂acts as an auto-propagating signaling molecule, possibly through Ca⁺² channel activation, and regulates gene expression involved in fertilization as well as post-fertilization development in red algae. </span></span></span><span><span><span>Reactive oxygen species (ROS) signaling has a multitude of roles in cellular processes throughout biology. We hypothesized that red algal fertilization may offer an interesting model to study ROS-mediated signaling as the stages of fertilization are complex and unique. </span></span></span><span><span><span>We microscopically localized ROS production and monitored the expression of three homologues of NADPH-oxidase in reproductive cells during fertilization. </span></span></span><span><span><span>ROSwere instantaneously produced by spermatia (sperm) when they attached to female trichogynes, diffused across the cell membrane in the form of H₂O₂, and triggered ROS generation in the carpogonium (egg) as well as carpogonial branch cells which are not in direct contact with spermatia. The expression of NADPH-oxidase homologues, <i>Bmrboh</i>s, began to be upregulated in the female plant upon gamete binding, peaking during the fertilization process and descending back to their original level after fertilization. Pretreatment with diphenylene iodonium (DPI) or caffeine blocked the gene expression as well as H₂O₂production. Post-fertilization development was also inhibited when the redox state of the plants were perturbed with H₂O₂ at any time before or after the fertilization. </span></span></span><span><span><span>Our results suggest that H₂O₂acts as an auto-propagating signaling molecule, possibly through Ca⁺² channel activation, and regulates gene expression involved in fertilization as well as post-fertilization development in red algae.</span></span></span></p>