Functional analysis for domains of maize PPR protein EMP5 in RNA editing and plant development in Arabidopsis

EMP5 and OTP72 are PPR proteins involved in mitochondrial same site RNA editing of rpl16 in maize and Arabidopsis, respectively. Besides rpl16, EMP5 also affects the editing efficiency of some editing sites in other mitochondrial transcripts. Loss of function of EMP5 causes arrested embryogenesis and endosperm development in maize, but no discernable defective phenotype is observed in Arabidopsis otp72 mutant plants. We here report that EMP5 can completely complement Arabidopsis otp72 for Ararpl16-440 editing, and E domain can't be disrupted for normal function of EMP5. An interesting finding was that overexpression of a set of truncated EMP5s in Col-0 resulted in delayed bolting phenotypes and smaller plants. It seems some truncated EMP5s, such as EMP5-C and EMP5-D, have yet unknown functions, are not responsible for Ararpl16-440 editing any more. The phylogenetic analysis indicated that the functions of most EMP5 orthologs may be conserved, but EMP5 ortholog proteins from Nicotiana and Solanum can't be found, and the C to U editing of Zmrpl16-458 site was not needed any more in the two species. Therefore, these two primary orthologs maybe already evolve new functions and change to different new proteins during evolutionary history. Overall, our studies revealed that E domain is crucial for mitochondrial RNA editing function of EMP5, and a set of truncated EMP5s still have functions for Arabidopsis normal growth and development, providing new insights into investigating the functions of EMP5 protein.