The Arabidopsis pentatricopeptide repeat protein PDM1 is associated with the intergenic sequence of S11-rpoA for rpoA monocistronic RNA cleavage

The PDM1 gene encodes a pentatricopeptide repeat protein of the PLS subfamily. It is essential for rpoA polycistronic processing in Arabidopsis. In this study, we performed functional analysis of PDM1 in rpoA monocistronic cleavage and chloroplast development. The pdm1 mutants display an albino lethal phenotype with severe chloroplast development defects. When the construct of PDM1 fused with the GFP gene was introduced into Arabidopsis protoplasts, the GFP signal was exclusively observed in chloroplasts. This shows that PDM1 is localized to chloroplast. In the wild type, the rpoA transcript of about 990 nt is processed. In pdm1, this transcript is absent. However, Western blot showed that the RpoA protein in pdm1 is accumulated at a level approximately 1/3 of the wild type. This suggests that certain other transcripts processed from L23-L2-S19-L22-S3-L16-L14-S8-L36-S11-rpoA polycistronic precursor may be used as templates for protein translation. To determine whether PDM1 can bind to the rpoA pre-mRNA, we generated a transgenic Arabidopsis line with PDM1 fused to FLAG tag that was capable of complementing the pdm1-1 mutant phenotype. RNA immunoprecipitation analysis showed that PDM1 is associated with S11-rpoA intergenic sequence. This indicates that PDM1 may bind to the S11-rpoA intergenic region to perform rpoA processing.