Plant organelles arose from two independent endosymbiosis events. Throughout evolutionary history, tight control of chloroplasts and mitochondria has been gained by the nucleus, which regulates most steps of organelle genome expression and metabolism. In particular, RNA maturation, including RNA splicing, is highly dependent on nuclearly encoded splicing factors. Most introns in organelles are group Ⅱ introns, whose catalytic mechanism closely resembles that of the nuclear spliceosome. Plant group Ⅱ introns have lost the ability to self-splice in vivo and require nuclearly encoded proteins as cofactors. Since the first splicing factor was identified in chloroplasts more than 10 years ago, many other proteins have been shown to be involved in splicing of one or more introns in chloroplasts or mitochondria. These new proteins belong to a variety of different families of RNA binding proteins and provide new insights into ribonucleoprotein complexes and RNA splicing machineries in organelles. In this review, we describe how splicing factors, encoded by the nucleus and targeted to the organelles, take part in post-transcriptional steps in higher plant organelle gene expression. We go on to discuss the potential for these factors to regulate organelle gene expression.
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