Role of Nadph-Oxidase Mediated Ros Signaling to Oomycete Infection in the Red Alga Dasysiphonia japonica

Plants are confronted with a myriad of challenges that they must mitigate without being able to move to new environments. Systemic acquired resistance (SAR) is a secondary immune response in plants to pathogen infection. Little is known about SAR in red algae. The red alga Dasysiphonia japonica can survive for more than six years without lethal damage when infected with the pathogen Olpidiopsis heterosiphoniae but dies within a month when infected with another pathogen, Olpidiopsis dasysiphoniae. During this process, D. japonica infected with O. heterosiphoniae accumulated reactive oxygen species (ROS, DCFH-DA staining) in the host cell membrane, whereas this was not observed with O. dasysiphoniae infection. Transcriptome analysis identified four NADPH-oxidase genes (Djrboh) that generate ROS in the cell membrane of D. japonica. Real-time PCR of four NADPH oxidase genes (Djrboh) showed that two were upregulated (Djrboh1, 2) at the onset of Olpidiopsis heterosiphoniae infection, but not during infection with O. dasysiphoniae in early infection that does not induce SAR. The successful SAR of D. japonica was mediated by low concentrations of ROS signaling and regulation of NADPH-oxidase genes.