bims-plasge Biomed News
on Plastid genes
Issue of 2019‒05‒19
two papers selected by
Vera S. Bogdanova
Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences

  1. Plant Cell Rep. 2019 May 11.
      Plant cells are characterized by a unique group of interconvertible organelles called plastids, which are descended from prokaryotic endosymbionts. The most studied plastid type is the chloroplast, which carries out the ancestral plastid function of photosynthesis. During the course of evolution, plastid activities were increasingly integrated with cellular metabolism and functions, and plant developmental processes, and this led to the creation of new types of non-photosynthetic plastids. These include the chromoplast, a carotenoid-rich organelle typically found in flowers and fruits. Here, we provide an introduction to non-photosynthetic plastids, and then review the structures and functions of chromoplasts in detail. The role of chromoplast differentiation in fruit ripening in particular is explored, and the factors that govern plastid development are examined, including hormonal regulation, gene expression, and plastid protein import. In the latter process, nucleus-encoded preproteins must pass through two successive protein translocons in the outer and inner envelope membranes of the plastid; these are known as TOC and TIC (translocon at the outer/inner chloroplast envelope), respectively. The discovery of SP1 (suppressor of ppi1 locus1), which encodes a RING-type ubiquitin E3 ligase localized in the plastid outer envelope membrane, revealed that plastid protein import is regulated through the selective targeting of TOC complexes for degradation by the ubiquitin-proteasome system. This suggests the possibility of engineering plastid protein import in novel crop improvement strategies.
    Keywords:  Chloroplast; Chromoplast; Organelle; Plastid; Plastid biogenesis; Plastid protein import; SP1
  2. J Exp Bot. 2019 May 14. pii: erz226. [Epub ahead of print]
      Pentatricopeptide repeat (PPR) proteins constitute one of the largest protein families in land plants. Recent studies revealed the functions of PPR proteins in organellar RNA metabolism and plant development, but the functions of most PPR proteins, especially PPRs localized in the nucleus, remain largely unknown. Here, we report the isolation and characterization of a rice mutant named floury and growth retardation1 (fgr1). fgr1 showed floury endosperm with loosely arranged starch grains, decreased starch and amylose contents, and retarded seedling growth. Map-based cloning showed the mutant phenotype was caused by a single nucleotide substitution in the coding region of Os08g0290000. This gene encodes a nucleus-localized PPR protein we named it OsNPPR1 that affected mitochondrial function. In vitro SELEX and RNA-EMSA assays showed that OsNPPR1 was an RNA protein that bound to the CUCAC motif determined. Moreover, a number of retained intron (RI) events were detected in fgr1. Thus, OsNPPR1 was involved in regulation of mitochondrial development and/or functions that are important for endosperm development. Our results provide novel insights into coordinated interaction between nucleus-localized PPR proteins and mitochondrial function.
    Keywords:  Pentatricopeptide repeat protein; floury endosperm; mitochondrial function; nucleus localization; retained intron; rice