Regulatory role of Arabidopsis pTAC14 in chloroplast development and plastid gene expression.

Transcriptionally active chromosome (TAC) is a fraction of protein/DNA complexes with RNA polymerase activity in the plastid. The function of most TAC proteins is not well known. We isolated a mutant gene encoding a plastid TAC component, pTAC14, and performed functional analysis of plastid gene expression and chloroplast development in Arabidopsis. We found that knockout of pTAC14 led to the blockage of thylakoid formation in the initial process of chloroplast development. Furthermore, the transcript levels of plastid-encoded polymerase (PEP)-dependent genes were downregulated in ptac14, suggesting that PEP activity was decreased in the mutant. On the basis of these results, we briefly review the available evidence and highlight the interaction between pTAC14 and pTAC12 that could help us understand the regulatory role of pTAC14 in chloroplast development and plastid gene expression.