A poly(A)-specific ribonuclease directly regulates the poly(A) status of mitochondrial mRNA in Arabidopsis.

Coordination of gene expression in the organelles and the nucleus is important for eukaryotic cell function. Transcriptional and post-transcriptional gene regulation in mitochondria remains incompletely understood in most eukaryotes, including plants. Here we show that poly(A)-specific ribonuclease, which influences the poly(A) status of cytoplasmic mRNA in many eukaryotes, directly regulates the poly(A) tract of mitochondrial mRNA in conjunction with a bacterial-type poly(A) polymerase, AGS1, in Arabidopsis. An Arabidopsis poly(A)-specific ribonuclease-deficient mutant, ahg2-1, accumulates polyadenylated mitochondrial mRNA and shows defects in mitochondrial protein complex levels. Mutations of AGS1 suppress the ahg2-1 phenotype. Mitochondrial localizations of AHG2 and AGS1 are required for their functions in the regulation of the poly(A) tract of mitochondrial mRNA. Our findings suggest that AHG2 and AGS1 constitute a regulatory system that controls mitochondrial mRNA poly(A) status in Arabidopsis.