Regulation Of Oxidative Signaling By Ascorbate Peroxidase In Chloroplasts

Abstract

Oxidative signaling via H₂O₂ is essential for plant response to environmental stress. Two types of ascorbate peroxidase are localized in thylakoid membrane (tAPX) and stroma (sAPX) of chloroplasts in higher plants. In order to clarify involvement of chloroplastic APX in the regulation of oxidative signaling via H₂O₂, we characterized single mutants lacking either tAPX or sAPX. Under high-light, H₂O₂ accumulated at higher levels in both mutants than the wild-type plants. However, the absence of sAPX or tAPX suppressed drastically the expression of H₂O₂-responsive genes under high-light. These findings suggest that H₂O₂ derived from chloroplasts negatively regulates H₂O₂-responsive genes under high-light. When the expression of tAPX was transiently suppressed by an estrogen inducible RNAi, the levels of oxidative protein increased in chloroplasts, and the expression of genes involved in several hormonal or stressful response was changed.