PTAC10Is Involved In PEP-dependent Chloroplast Gene Transcription And Expression

The S1domain-containing protein, pTAC10was previously identifed as a componentof the transcriptionally active chromsome (TAC) complexes. Here, we investigatedthe function of it in the regulation of plastid-encoded bacterialtype RNA polymerase(PEP) activity and chloroplast development. The knockout of this protein led to theblockage of thylakoid formation in Arabidopsis, and the mutant was seedling lethal.Sequence and transcriptional analysis showed pTAC10encodes a specifc protein inplants that is located in the chloroplast associated with the thylakoid and that itsexpression depends on light. In addition, the transcript levels of all investigatedPEP-dependent genes were clearly reduced in the mutants, while the accumulation ofnucleus-encoded phage-type RNA polymerase-dependent transcripts was increased,indicating an important role of pTAC10in maintaining PEP activity. pTAC10wasfound to interact with a thioredoxin Trxz, another component of TACs. pTAC10is asubstrate for regulatory phosphorylation by a nuclear-coded plastid-targeted caseinkinase2(cpCK2) both in vitro and in vivo. We present data suggesting that pTAC10is essential for proper chloroplast development, most likely by affecting PEP activityand regulating PEP-dependent plastid gene transcription in Arabidopsis together withTrxz and cpCK2.