Modulation of O-mediated retrograde signaling by the PLEIOTROPIC RESPONSE LOCUS 1 (PRL1) protein, a central integrator of stress and energy signaling.

Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts, changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. Extensive genetic screens aimed at identifying constituents involved in (1)O(2)-mediated plastid-to-nucleus signaling have failed to identify extraplastidic signaling components. This finding suggests that (1)O(2)-mediated signals are not translocated to the nucleus via a single linear pathway, but rather through a signaling network that is difficult to block by single mutations. The complexity of this signaling network has been tackled by mutagenizing a transgenic flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second site mutants that constitutively express the reporter gene at a high level. One of the mutants was shown by map-based cloning and sequencing to contain a single amino acid change in the PLEIOTROPIC RESPONSE LOCUS 1 (PRL1) protein. PRL1 suppresses the expression of AAA-ATPase and other (1)O(2)-responsive genes. PRL1 seems to play a major role in modulating responses of plants to environmental changes by interconnecting (1)O(2)-mediated retrograde signaling with other signaling pathways.

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