Function Analysis Of Arabidopsis PPR Protein PDM1Involving In RpoA Gene Posttranscription Expression

The PDM1gene encodes a pentatricopeptide repeat protein of thePLS subfamily. It is essential for rpoA polycistronic processing inArabidopsis. In this study, we performed functional analysis of PDM1inrpoA monocistronic cleavage and chloroplast development. The pdm1mutants display an albino lethal phenotype with severe chloroplastdevelopment defects. When the construct of PDM1fused with the GFPgene was introduced into Arabidopsis protoplasts, the GFP signal wasexclusively observed in chloroplasts. This shows that PDM1is localized tochloroplast. In the wild type, the rpoA transcript of about990nt isprocessed. In pdm1, this transcript is absent. We analyzed thetranscription pattern of atpB. In pdm1-1mutant the2.6kb transcriptionunit transcribed by PEP (plastid-enconded polymerase) was absentwhile wild type had both the transcription units produced by NEP(nucleus-encoded polymerase) and PEP. This result indicates that PEPactivity is impaired in pdm1-1. However, Western blot showed that theRpoA protein in pdm1is accumulated at a level approximately1/3ofthe wild type. This suggests that certain other transcripts processed fromL23-L2-S19-L22-S3-L16-L14-S8-L36-S11-rpoA polycistronic precursor maybe used as templates for protein translation. To determine whetherPDM1can bind to the rpoA pre-mRNA, we generated a transgenicArabidopsis line with PDM1fused to FLAG tag that was capable ofcomplementing the pdm1-1mutant phenotype. RNAimmunoprecipitation analysis showed that PDM1is associated withS11-rpoA intergenic sequence. This indicates that PDM1may bind to theS11-rpoA intergenic region to perform rpoA processing.