bims-plasge Biomed News
on Plastid genes
Issue of 2022‒03‒06
four papers selected by
Vera S. Bogdanova
Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences

  1. New Phytol. 2022 Mar 04.
      RNA C-to-U editing is important to the expression and function of organellar genes in plants. Despite several families of proteins have been identified to participate in this process, the underlying mechanism is not fully understood. Here we report the function of EMP80 in the C-to-U editing at the nad7-769 and atp4-118 sites, and the potential recruitment of ZmDYW2 as a trans deaminase in maize (Zea mays) mitochondria. Loss of EMP80 function arrests embryogenesis and endosperm development in maize. EMP80 is a PPR-E+ protein localized to mitochondria. An absence of EMP80 abolishes the C-to-U RNA editing at nad7-769 and atp4-118 sites, resulting in a Cysteine-to-Arginine (CysArg) change in Nad7 and Atp4 in the emp80 mutant. The amino acid change consequently reduces the assembly of complex I and V, leading to an accumulation of the F1 - sub-complex of complex V. EMP80 was found to interact with atypical DYW-type PPR protein ZmDYW2, which interacts with ZmNUWA. Co-expression of ZmNUWA enhances the interaction between EMP80 and ZmDYW2, suggesting that EMP80 potentially recruits ZmDYW2 as a trans deaminase through protein-protein interaction, and ZmNUWA may function as an enhancer of this interaction.
    Keywords:  EMP80; PPR protein; RNA editing; ZmDYW2; ZmNUWA; maize (Zea mays); mitochondria
  2. Plant J. 2022 Feb 27.
      Heteromeric acetyl-CoA carboxylase (htACCase) catalyzes the committed step of de novo fatty acid biosynthesis in most plant plastids. Plant htACCase is comprised of four subunits: α-and β-carboxyltransferase (α- and β-CT), biotin carboxylase, and biotin carboxyl carrier protein. Based on in vivo absolute quantification of htACCase subunits, α-CT is 3- to 10-fold less abundant than its partner subunit β-CT in developing Arabidopsis seeds [Wilson and Thelen, J. Proteome Res., 2018, 17 (5)]. To test the hypothesis that low expression of α-CT limits htACCase activity and flux through fatty acid synthesis in planta, we overexpressed Pisum sativum α-CT, either with or without its non-catalytic, C-terminal domain, in both Arabidopsis thaliana and Camelina sativa. First generation Arabidopsis seed of 35S::Ps α-CT (n = 25) and 35S::Ps α-CTΔ406-875 (n = 47) were on average 14% higher in oil content (% DW) than wild-type co-cultivated in a growth chamber. First generation Camelina seed showed an average 8% increase compared to co-cultivated wild-type. Biochemical analyses confirmed the accumulation of Ps α-CT and Ps α-CTΔ406-875 protein and higher htACCase activity in overexpression lines during early seed development. Overexpressed Ps α-CT co-migrated with native At β-CT during anion exchange chromatography, indicating co-association. By successfully increasing seed oil content upon heterologous over-expression of α-CT, we demonstrate how absolute quantitation of in vivo protein complex stoichiometry can be used to guide rational metabolic engineering.
    Keywords:  Camelina sativa; CoA carboxylase (ACCase); absolute protein quantification; alpha-carboxyltransferase; fatty acid biosynthesis; rational metabolic engineering; subunit stoichiometry
  3. Front Plant Sci. 2022 ;13 815859
      Although numerous studies have been carried out on chloroplast development and biogenesis, the underlying regulatory mechanisms are still largely elusive. Here, we characterized a chloroplast stromal protein Chloroplast Development and Biogenesis1 (CDB1). The knockout cdb1 mutant exhibits a seedling-lethal and ivory leaf phenotype. Immunoblot and RNA blot analyses show that accumulation of chloroplast ribosomes is compromised in cdb1, resulting in an almost complete loss of plastid-encoded proteins including the core subunits of the plastid-encoded RNA polymerase (PEP) RpoB and RpoC2, and therefore in impaired PEP activity. Orthologs of CDB1 are found in green algae and land plants. Moreover, a protein shows high similarity with CDB1, designated as CDB1-Like (CDB1L), is present in angiosperms. Absence of CDB1L results in impaired embryo development. While CDB1 is specifically located in the chloroplast stroma, CDB1L is localized in both chloroplasts and mitochondria in Arabidopsis. Thus, our results demonstrate that CDB1 is indispensable for chloroplast development and biogenesis through its involvement in chloroplast ribosome assembly whereas CDB1L may fulfill a similar function in both mitochondria and chloroplasts.
    Keywords:  CDB1; CDB1L; chloroplast; mitochondria; ribosome
  4. Nat Commun. 2022 Mar 03. 13(1): 1133
      Most sexual organisms inherit organelles from one parent, commonly by excluding organelles from the smaller gametes. However, post-mating elimination of organelles derived from one gamete ensures uniparental inheritance, where the underlying mechanisms to distinguish organelles by their origin remain obscure. Mating in Chlamydomonas reinhardtii combines isomorphic plus and minus gametes, but chloroplast DNA from minus gametes is selectively degraded in zygotes. Here, we identify OTU2p (otubain protein 2), encoded in the plus mating-type locus MT+, as the protector of plus chloroplast. Otu2p is an otubain-like deubiquitinase, which prevents proteasome-mediated degradation of the preprotein translocase of the outer chloroplast membrane (TOC) during gametogenesis. Using OTU2p-knockouts and proteasome inhibitor treatment, we successfully redirect selective DNA degradation in chloroplasts with reduced TOC levels regardless of mating type, demonstrating that plus-specific Otu2p establishes uniparental chloroplast DNA inheritance. Our work documents that a sex-linked organelle quality control mechanism drives the uniparental organelle inheritance without dimorphic gametes.