SIG5 closes a regulatory loop adjusting chloroplast and nuclear gene expression.

As a sigma factor, SIG5 controls expression of chloroplast genes, including the genes for the photoreaction center proteins D1 and D2. It own expression is under control of red and blue-light responsive photoreceptors and signals originating at the PQ-site of photosystem II.

For more details: Mellenthin et al. (2014) Plants 3, 359 - 391

RCD1 (radical incuded cell death 1) supports transcriptional activation of genes for chloroplast antioxidant enzymes.

RCD1, which protects plant cells from running into cell death, is allelic to RIMB1, which we have shown previously (Heiber et al., 2007) to be essential for full activation of genes for components of the chloroplast antioxidant system, such as peroxiredoxins and ascorbate peroxidases, and for biosynthesis of the glutathione and phytochelatin precursor gamma-glutamyl cysteine. In “Frontiers in Plant Science” we propose a regulatory circuitry in which RCD1 maintains plant cell vitality by stabilizing the redox-sensitive transcription factor Rap2.4a in activation of genes for chloroplast antioxidant enzymes based on gene expression and protein-protein-interaction studies and discuss rcd1-phenotypes in context of regulation of the chloroplast antioxidant system.

For more details: Hiltscher et al. (2014) Frontiers in Plant Science