Functional Characterization Of PDM1 Protein In Arabidopsis Thaliana

In higher plants chloroplast genes are transcribed by two types of RNA polymerases:nuclear-encoded polymerase (NEP) and plastid-encoded polymerase (PEP). NEP is mainly responsible for transcribing the components of the transcription/translation machinery, such as rpoA and rpoB, while PEPs are required for transcription of photosynthetic genes (such as psbA, psbD and rbcL). NEP is composed of a single submit, and PEPs contain core subunits encoded by rpoA, rpoB, rpoCl and rpoC2 genes.Pentratricopepite repeat (PPR) proteins, which are defined by the degenerate tandem array of 35 amino acids, have been shown to be important for the post-transcriptional gene expression. In the Arabidopsis thaliana genome, the PPR family is comprised of 466 members and more than 70%of the PPR proteins were targeted to either mitochondria or plastids. In the chloroplasts, PPR proteins were revealed to be involved in RNA splicing, RNA editing, RNA stability, ribosome accumulation and the early chloroplast gene expression.In this study, we identified and characterized a T-DNA insertion Arabidopsis pigment-deficient mutant named pdml with albino phenotype. PDM1 contains 5 PPR domains at its N-terminus followed by a PLS domain. In the pdml mutant, the levels of PEP-dependent chloroplast gene transcripts were greatly reduced, while the levels of NEP-dependent transcripts were increased. This suggests that PDM1 is involved in the regulation of the PEP activities. Similarly to those in mutants that are impaired in the function of PEP, Pdml displays an albino phenotype. Accordingly, the accumulation of thylakoid proteins in pdml was decreased substantially. The transcript pattern of L23-L2-S19-L22-S3-L16-L14-S8-L36-S11-rpoA pre-mRNA was altered and the spliced monocistronic rpoA transcript of 1000 nucleotides was not detected in pdml. The lack of ropA transcript in the pdml mutant may be responsible for the mutant phenotype. Thus, PDM1 protein may be involved in the splicing or stability of the Arabidopsis rpoA pre-mRNA.