Functional study of PAP3/pTAC10 in the plastid-encoded RNA polymerase during chloroplast biogenesis
DOI:
https://doi.org/10.24193/subbbiol.2026.1.04Keywords:
chloroplast biogenesis, PAP3, photobodies, phytochrome B, plastid-encoded RNA polymeraseAbstract
Chloroplast biogenesis in angiosperms depends on two types of RNA polymerases: the nuclear-encoded RNA polymerase (NEP) and the plastid-encoded RNA polymerase (PEP). PEP, in its active form (PEP-A), is supported by multiple nuclear-encoded proteins called PEP-associated proteins (PAPs). Among these, PAP3 (also known as pTAC10) plays a structural role in the PEP complex. Epifluorescent microscopy was used in order to verify its localization, confirming that PAP3 has a single subcellular localization: the chloroplast. Using the Arabidopsis thaliana pap3-1 mutant and PHYB-GFP (PBG) reporter lines, we demonstrate that PAP3 is not required for PHYB-mediated light signaling pathway nor for photobody formation. Contrary to PAP8, whose loss of function affects red light signaling and photobody formation, pap3 mutants show normal hypocotyl de-etiolation and photobody assembly under red light. These results suggest that in contrast with the nucleo-chloroplastic PAP8, PAP3 is confined to the plastid compartment and that it contributes exclusively to the plastidial transcriptional machinery. The difference in behavior between pap8 and pap3 mutants implements the existence of two distinct albino syndromes in PAPs, depending on their localization: dually localized (nucleus and chloroplasts) or solely localized (chloroplasts).
Article history: Received 30 July 2025; Revised 24 February 2026;
Accepted 30 April 2026; Available online 25 June 2026.
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