Involved in redox-mediated retrograde signaling to synchronize the expression of photosynthetic genes from both the nuclear and plastidic genomes, especially in excess light conditions (PubMed:22211401). Required for full expression of genes transcribed by the plastid-encoded RNA polymerase (PEP) (PubMed:22211401, PubMed:25161659). Essential for embryo development (PubMed:25161659). Binds DNA when in complex with CSP41b. Misregulation of photosynthesis-associated nuclear gene expression in response to excess light, and inhibition of photosynthetic electron transport (PubMed:22211401, PubMed:25161659). Defects in embryo development (PubMed:25161659). Dwarf pale plants (PubMed:22211401, PubMed:25161659). The csp41b-2 prin2-2 double mutant is embryo lethal (PubMed:25161659).