bims-plasge 2019-06-16 papers

Issue of 2019–06–16
three papers selected by
Vera S. Bogdanova, ИЦиГ СО РАН

BMC Plant Biol. 2019 Jun 07. 19(1): 244

A chloroplast-targeted pentatricopeptide repeat protein PPR287 is crucial for chloroplast function and Arabidopsis development.

Kwanuk Lee, Su Jung Park, Ji Hoon Han, Young Jeon, Hyun-Sook Pai, Hunseung Kang.

BACKGROUND: Even though the roles of pentatricopeptide repeat (PPR) proteins are essential in plant organelles, the function of many chloroplast-targeted PPR proteins remains unknown. Here, we characterized the function of a chloroplast-localized PPR protein (At3g59040), which is classified as the 287th PPR protein among the 450 PPR proteins in Arabidopsis ( http://ppr.plantenergy.uwa.edu.au ).
RESULTS: The homozygous ppr287 mutant with the T-DNA inserted into the last exon displayed pale-green and yellowish phenotypes. The microRNA-mediated knockdown mutants were generated to further confirm the developmental defect phenotypes of ppr287 mutants. All mutants had yellowish leaves, shorter roots and height, and less seed yield, indicating that PPR287 is crucial for normal Arabidopsis growth and development. The photosynthetic activity and chlorophyll content of ppr287 mutants were markedly reduced, and the chloroplast structures of the mutants were abnormal. The levels of chloroplast rRNAs were decreased in ppr287 mutants.
CONCLUSIONS: These results suggest that PPR287 plays an essential role in chloroplast biogenesis and function, which is crucial for the normal growth and development of Arabidopsis.

Keywords: Arabidopsis thaliana; Chloroplast; Development; PPR; RNA metabolism

DOI: https://doi.org/10.1186/s12870-019-1857-0

Protein J. 2019 Jun 14.

The TOC GTPase Receptors: Regulators of the Fidelity, Specificity and Substrate Profiles of the General Protein Import Machinery of Chloroplasts.

Danny J Schnell.

More than 2500 nuclear encoded preproteins are required for the function of chloroplasts in terrestrial plants. These preproteins are imported into chloroplasts via the concerted action of two multi-subunit translocons of the outer (TOC) and inner (TIC) membranes of the chloroplast envelope. This general import machinery functions to recognize and import proteins with high fidelity and efficiency to ensure that organelle biogenesis is properly coordinated with developmental and physiological events. Two components of the TOC machinery, Toc34 and Toc159, act as the primary receptors for preproteins at the chloroplast surface. They interact with the intrinsic targeting signals (transit peptides) of preproteins to mediate the selectivity of targeting, and they contribute to the quality control of import by constituting a GTP-dependent checkpoint in the import reaction. The TOC receptor family has expanded to regulate the import of distinct classes of preproteins that are required for remodeling of organelle proteomes during plastid-type transitions that accompany developmental changes. As such, the TOC receptors function as central regulators of the fidelity, specificity and selectivity of the general import machinery, thereby contributing to the integration of protein import with plastid biogenesis.

Keywords: Chloroplast biogenesis; Chloroplast protein import; Endosymbiosis; Protein quality control; Protein targeting; Transit peptide

DOI: https://doi.org/10.1007/s10930-019-09846-3

Integr Comp Biol. 2019 Jun 11. pii: icz102. [Epub ahead of print]

Heteroplasmy and Patterns of Cytonuclear Linkage Disequilibrium in Wild Carrot.

Adam J Ramsey, David E McCauley, Jennifer R Mandel.

Organellar genomes are considered to be strictly uniparentally-inherited. Uniparental inheritance allows for cytonuclear coevolution and the development of highly coordinated cytonuclear interactions. Yet, instances of biparental inheritance have been documented across eukaryotes. Biparental inheritance in otherwise uniparentally-inherited organelles is termed leakage (maternal or paternal) and allows for the presence of multiple variants of the same organellar genome within an individual, called heteroplasmy. It is unclear what, if any, evolutionary consequences are placed on nuclear and/or organellar genomes due to heteroplasmy. One way of accessing cytonuclear interactions and potential coevolution is through calculating cytonuclear linkage disequilibrium, or the non-random association of alleles between nuclear and organellar genomes. Patterns of cytonuclear LD (cnLD) can indicate positive or negative cytonuclear selection, coevolution between the nuclear and organellar genomes, non-traditional organellar inheritance, or instances of ancestral heteroplasmy. In plants, cytonuclear interactions have been shown to play a role in cytoplasmic male sterility (CMS) which occurs in gynodioecious species and is associated with leakage. We used the gynodioecious species, Daucus carota L. spp. carota, or wild carrot, to investigate cnLD. We genotyped a total of 265 individuals from two regions of the United States at 15 nuclear microsatellites, the mitochondrial genes cox1 and atp9, and an intergenic region between trnS and trnG (StoG) in the plastid genome to calculate nuclear-nuclear LD (nucLD), cnLD, and organellar LD (i.e. within the mtDNA and between mtDNA and ptDNA) within the two regions. We were further able to identify cox1 and StoG heteroplasmy and calculate some of the same LD measures within heteroplasmic and homoplasmic (non-heteroplasmic) datasets. We used a Z-transformation test to demonstrate that heteroplasmic individuals display significantly higher levels of cnLD within both regions. In spite of this, within and between organellar LD is low to moderate. Given these patterns of LD in two regions of the US in which gene flow has been shown to occur between crop and wild carrot, we suggest that heteroplasmy is an evolutionary mechanism which permits the maintenance of cnLD while also acting to disrupt organellar LD.

Keywords: cytonuclear interactions; leakage; mtDNA; organellar LD; ptDNA

DOI: https://doi.org/10.1093/icb/icz102