The PAC protein affects the maturation of specific chloroplast mRNAs in Arabidopsis thaliana.

The pale cress (pac) mutation arrests chloroplast development at an early stage in Arabidopsis thaliana and leads to a white phenotype. Chlorophyll fluorescence measurements demonstrated that the photosynthetic apparatus was impaired. The mutation did not reduce transcription of nuclear genes with photosynthetic function. However, distinct chloroplast-encoded transcripts were affected. The mutation mainly changed the maturation pattern, but the abundance of specific transcripts was also reduced. The defects observed imply a specific role for PAC in chloroplast mRNA maturation. PAC is encoded by a nuclear gene and is transported into the chloroplast. Therefore PAC may be one of the nucleus-encoded factors that function in plastid mRNA maturation and accumulation.