HO response gene 1/2 are novel sensors or responders of HO and involve in maintaining embryonic root meristem activity in Arabidopsis thaliana.

Signal molecule hydrogen peroxide (HO) plays critical roles in various processes of plant development. However, HO signaling network, especially the responders that sense and respond to the HO signal remain largely unknown. Here we report two homologous genes HO Response Gene 1 and 2 (HRG1/2) in Arabidopsis that could quickly respond to exogenous or endogenous HO. Knockdown of HRG1/2 facilitated seed germination while overexpression of HRG1/2 greatly retarded seed germination. ROS level in HRG1 overexpression roots was significantly lower than that in HRG1/2 mutants after HO treatment. The expression level of enzymatic antioxidant DHAR3 was upregulated in HRG1 overexpression plants, suggesting that DHAR3 is downstream of HRG1. That the root meristem length and cell number were significantly reduced in hrg1-1 and hrg2-1 plants upon HO treatment compared to that of HRG1 overexpression plants also approves the idea that HRGs function in HO removal. Further evolutionary analysis indicates that this is a dicotyledon-specific pathway responsive to HO. Together, this work reveals HRG1/2 as novel HO responders involved in ROS scavenging to ensure embryonic root meristem activity. These findings provide valuable clues for the of HO signaling and root meristem regulation.