bims-plasge Biomed News
on Plastid genes
Issue of 2021‒01‒03
two papers selected by
Vera S. Bogdanova
Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences

  1. Theor Appl Genet. 2021 Jan 02.
      KEY MESSAGE: P-subfamily PPR protein OsPPR939, which can be phosphorylated by OsS6K1, regulates plant growth and pollen development by involving in the splicing of mitochondrial nad5 introns 1, 2, and 3. In land plants, pentatricopeptide repeat (PPR) proteins play key roles in mitochondrial group II intron splicing, but how these nucleus-encoded proteins are imported into mitochondria is unknown. To date, a few PPR proteins have been characterized in rice (Oryza sativa). Here, we demonstrate that the mitochondrion-localized P-subfamily PPR protein OsPPR939 is required for the splicing of nad5 introns 1, 2, and 3 in rice. Complete knockout or partial disruption of OsPPR939 function resulted in different degrees of growth retardation and pollen sterility. The dramatically reduced splicing efficiency of these introns in osppr939-4 and osppr939-5 led to reduced mitochondrial complex I abundance and activity and enhanced expression of alternative respiratory pathway genes. Complementation with OsPPR939 rescued the defective plant morphology of osppr939-4 and restored its decreased splicing efficiency of nad5 introns 1, 2, and 3. Therefore, OsPPR939 plays crucial roles in plant growth and pollen development by splicing mitochondrial nad5 introns 1, 2, and 3. More importantly, the 12th amino acid Ser in the N-terminal targeting sequence of OsPPR939 is phosphorylated by OsS6K1, and truncated OsPPR939 with a non-phosphorylatable S12A mutation in its presequence could not be imported into mitochondria, suggesting that phosphorylation of this amino acid plays an important role in the mitochondrial import of OsPPR939. To our knowledge, the 12th residue Ser on OsPPR939 is the first experimentally proven phosphorylation site in PPR proteins. Our results provide a basis for investigating the regulatory mechanism of PPR proteins at the post-translational level.
  2. Plant Cell Physiol. 2020 Dec 30. pii: pcaa161. [Epub ahead of print]
      Splicing of plant organellar group II introns from precursor-RNA transcripts requires the assistance of nuclear-encoded splicing factors. Maturase (nMAT) is a kind of such factors, as its three homologs (nMAT1, 2, and 4) has been identified for splicing of various mitochondrial introns in Arabidopsis. However, function of nMAT in maize (Zea mays L.) is unknown. In this study, we identified a seed development mutant, Empty Pericarp 2441 (emp2441) from maize, which showed severely arrested embryogenesis and endosperm development. Positional cloning and transgenic complementation assays revealed that Emp2441 encoded a maturase-related protein, ZmnMAT3. ZmnMAT3 highly expressed during seed development and its protein located in the mitochondria. The loss-of-function of ZmnMAT3 resulted in reduced splicing efficiency of various mitochondrial group II introns, particularly of the trans-splicing of nad1 intron 1, 3, and 4, which consequently abolished the transcript of nad1 and severely impaired the assembly and activity of mitochondrial complex I. Moreover, the Zmnmat3 mutant showed defective mitochondrial structure and induced the expression and activity of alternative oxidases. These results indicated that ZmnMAT3 is essential for mitochondrial complex I assembly during kernel development in maize.
    Keywords:  RNA splicing; kernel development; maize; maturase; mitochondria; nad1