Trans-splicing of plastid rps12 transcripts, mediated by AtPPR4, is essential for embryo patterning in Arabidopsis thaliana
AtPPR4-mediated trans-splicing of plastid rps12 transcripts is essential for key embryo morphogenetic events such as development of cotyledons, determination of provascular tissue, and organization of the shoot apical meristem (SAM), but not for the formation of the protodermal layer.
Members of the pentatricopeptide repeat (PPR) containing protein family have emerged as key regulators of the organelle post-transcriptional processing and to be essential for proper plant embryo development. In this study, we report the functional characterization of the AtPPR4 (At5g04810) gene encoding a plastid nucleoid PPR protein. In-situ hybridization analysis reveals the presence of AtPPR4 transcripts already at the transition stage of embryo development. As a consequence, embryos lacking the AtPPR4 protein arrest their development at the transition/early-heart stages and show defects in the determination of the provascular tissue and organization of SAM. This complex phenotype is due to the specific role of AtPPR4 in the trans-splicing of the plastid rps12 transcripts, as shown by northern and slot-blot hybridizations, and the consequent defect in 70S ribosome accumulation and plastid protein synthesis, in agreement with the role proposed for the maize orthologue, ZmPPR4.
KeywordsChloroplast Embryo development Pentatricopeptide repeat protein Protein synthesis RNA metabolism
Shoot apical meristem
We are grateful to Christian Schmitz-Linneweber and members of his lab for their support in nucleotide immunoprecipitation and slot-blot analysis, and to Matteo Arosio for the help with the isolation of atppr4 mutant lines. We thank Valerio Parravicini and Mario Beretta for their excellent care of plants.
R. F. was supported by a Ph.D. fellowship from the Università degli Studi di Milano, C. M. and L. T. by a MIUR post-doc fellowship. Work in the lab of S. M. and P. P. was funded by CARIPLO Foundation (Grant no. 2011-2257).
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