Cross-talk between singlet oxygen- and hydrogen peroxide-dependent signaling of stress responses in Arabidopsis thaliana

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Abstract
Upon a dark-to-light shift, the conditional fluorescent ( flu ) mutant of Arabidopsis releases singlet oxygen ( 1 O 2 ) within the plastid compartment. Distinct sets of nuclear genes are activated that are different from those induced by superoxide (O 2 •− ) and/or hydrogen peroxide (H 2 O 2 ), suggesting that different types of reactive oxygen species activate distinct signaling pathways. It is not known whether the pathways operate separately or interact with each other. We have addressed this problem by modulating noninvasively the level of H 2 O 2 in plastids by means of a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX). The overexpression of the H 2 O 2 -specific scavenger reduced strongly the activation of nuclear genes in plants treated with the herbicide paraquat that in the light leads to the enhanced generation of O 2 •− and H 2 O 2 . In the flu mutant overexpressing tAPX, the intensity of 1 O 2 -mediated cell death and growth inhibition was increased when compared with the flu parental line. Also, the expression of most of the nuclear genes that were rapidly activated after the release of 1 O 2 was significantly higher in flu plants overexpressing tAPX, whereas in wild-type plants, overexpression of tAPX did not lead to visible stress responses and had only a very minor impact on nuclear gene expression. The results suggest that H 2 O 2 antagonizes the 1 O 2 -mediated signaling of stress responses as seen in the flu mutant. This cross-talk between H 2 O 2 - and 1 O 2 -dependent signaling pathways might contribute to the overall stability and robustness of wild-type plants exposed to adverse environmental stress conditions.