IREN, a novel EF-hand motif-containing nuclease, functions in the degradation of nuclear DNA during the hypersensitive response cell death in rice

The hypersensitive response (HR), a type of programmed cell death that is accompanied by DNA degradation and loss of plasma membrane integrity, is a common feature of plant immune responses. We previously reported that transcription of <i>IREN</i> which encodes a novel EF-hand containing plant nuclease is controlled by OsNAC4, a key positive regulator of HR cell death. Transient overexpression of IREN in rice protoplasts also led to rapid DNA fragmentation, while suppression of IREN using RNA interference showed remarkable decrease of DNA fragmentation during HR cell death. Maximum DNA degradation associated with the recombinant IREN was observed in the presence of Ca²⁺ and Mg²⁺ or Ca²⁺ and Mn²⁺. Interestingly, DNA degradation mediated by the recombinant IREN was completely abolished by Zn²⁺, even when Ca²⁺, Mg²⁺, or Mn²⁺ were present in the reaction buffer. These data indicate that IREN functions in the degradation of nuclear DNA during HR cell death. IREN, novel EF-hand containing plant nuclease, functions in the degradation of nuclear DNA during immune-related hypersensitive cell death.