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Multiple RNA processing defects and impaired chloroplast function in plants deficient in the organellar protein-only RNase P enzyme.

Zhou W, Karcher D, Fischer A, Maximova E, Walther D, Bock R - PLoS ONE (2015)

Bottom Line: PRORP1 knock-down lines show defects in photosynthesis, while mitochondrial respiration is not appreciably affected.In both plastids and mitochondria, the effects of PRORP1 knock-down on the processing of individual tRNA species are highly variable.The drastic reduction in the levels of mature plastid tRNA-Phe(GAA) and tRNA-Arg(ACG) suggests that these two tRNA species limit plastid gene expression in the PRORP1 mutants and, hence, are causally responsible for the mutant phenotype.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Potsdam-Golm, Germany.

ABSTRACT
Transfer RNA (tRNA) precursors undergo endoribonucleolytic processing of their 5' and 3' ends. 5' cleavage of the precursor transcript is performed by ribonuclease P (RNase P). While in most organisms RNase P is a ribonucleoprotein that harbors a catalytically active RNA component, human mitochondria and the chloroplasts (plastids) and mitochondria of seed plants possess protein-only RNase P enzymes (PRORPs). The plant organellar PRORP (PRORP1) has been characterized to some extent in vitro and by transient gene silencing, but the molecular, phenotypic and physiological consequences of its down-regulation in stable transgenic plants have not been assessed. Here we have addressed the function of the dually targeted organellar PRORP enzyme in vivo by generating stably transformed Arabidopsis plants in which expression of the PRORP1 gene was suppressed by RNA interference (RNAi). PRORP1 knock-down lines show defects in photosynthesis, while mitochondrial respiration is not appreciably affected. In both plastids and mitochondria, the effects of PRORP1 knock-down on the processing of individual tRNA species are highly variable. The drastic reduction in the levels of mature plastid tRNA-Phe(GAA) and tRNA-Arg(ACG) suggests that these two tRNA species limit plastid gene expression in the PRORP1 mutants and, hence, are causally responsible for the mutant phenotype.

No MeSH data available.


Related in: MedlinePlus

Transmission electron microscopic images of chloroplasts and mitochondria in 15-day-old leaves from PRORP1 RNAi mutants and wild-type plants.(A, B) Ultrastructure of chloroplasts and mitochondria in wild-type cells. For easy organelle identification, a chloroplast (P) and a mitochondrion (M) are labeled. (C-E) Ultrastructure of chloroplasts and mitochondria in cells of the strong PRORP1 RNAi mutant line RNAi-2. Note smaller chloroplasts with more pronounced grana stacking and bigger, more elongated mitochondria. (F) Ultrastructure of chloroplasts and mitochondria in line RNAi-5. (G) Chloroplast ultrastructure in the weakest RNAi line (RNAi-12). Scale bars: 1 μm.
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pone.0120533.g003: Transmission electron microscopic images of chloroplasts and mitochondria in 15-day-old leaves from PRORP1 RNAi mutants and wild-type plants.(A, B) Ultrastructure of chloroplasts and mitochondria in wild-type cells. For easy organelle identification, a chloroplast (P) and a mitochondrion (M) are labeled. (C-E) Ultrastructure of chloroplasts and mitochondria in cells of the strong PRORP1 RNAi mutant line RNAi-2. Note smaller chloroplasts with more pronounced grana stacking and bigger, more elongated mitochondria. (F) Ultrastructure of chloroplasts and mitochondria in line RNAi-5. (G) Chloroplast ultrastructure in the weakest RNAi line (RNAi-12). Scale bars: 1 μm.

Mentions: To assess the consequences of PRORP1 suppression at the ultrastructural level, chloroplasts and mitochondria were analyzed by transmission electron microscopy (Fig. 3). Conspicuous changes were seen in both chloroplast and mitochondrial ultrastructure, which were most pronounced in the strongest RNAi line, RNAi-2. Chloroplasts were smaller than in wild-type cells and displayed a somewhat more intense stacking of grana thylakoids. This observation is in line with the chlorophyll a:b ratio being decreased in the mutants (2.43±0.13 in the wild type versus 2.16±0.17 in line RNAi-2; Fig. 1E), which was found to correlate with increased grana stacking also in other mutants with impaired chloroplast function [42]. Mitochondrial shape was also altered in the PRORP1 RNAi lines. Whereas, in wild-type cells, mitochondria were round or oval, they were bigger and much more elongated in the mutants, especially in cells of the RNAi-2 line (Fig. 3). In contrast to the previously reported transient repression of PRORP1 (by virus-induced gene silencing; [8]), we did not observe “dense mitochondrial structures containing vacuoles”. Whether this alteration in mitochondrial morphology represents a direct compensatory response to impaired mitochondrial gene expression or rather an indirect consequence of disturbed chloroplast function in the RNAi mutants, remains to be determined.


Multiple RNA processing defects and impaired chloroplast function in plants deficient in the organellar protein-only RNase P enzyme.

Zhou W, Karcher D, Fischer A, Maximova E, Walther D, Bock R - PLoS ONE (2015)

Transmission electron microscopic images of chloroplasts and mitochondria in 15-day-old leaves from PRORP1 RNAi mutants and wild-type plants.(A, B) Ultrastructure of chloroplasts and mitochondria in wild-type cells. For easy organelle identification, a chloroplast (P) and a mitochondrion (M) are labeled. (C-E) Ultrastructure of chloroplasts and mitochondria in cells of the strong PRORP1 RNAi mutant line RNAi-2. Note smaller chloroplasts with more pronounced grana stacking and bigger, more elongated mitochondria. (F) Ultrastructure of chloroplasts and mitochondria in line RNAi-5. (G) Chloroplast ultrastructure in the weakest RNAi line (RNAi-12). Scale bars: 1 μm.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4368725&req=5

pone.0120533.g003: Transmission electron microscopic images of chloroplasts and mitochondria in 15-day-old leaves from PRORP1 RNAi mutants and wild-type plants.(A, B) Ultrastructure of chloroplasts and mitochondria in wild-type cells. For easy organelle identification, a chloroplast (P) and a mitochondrion (M) are labeled. (C-E) Ultrastructure of chloroplasts and mitochondria in cells of the strong PRORP1 RNAi mutant line RNAi-2. Note smaller chloroplasts with more pronounced grana stacking and bigger, more elongated mitochondria. (F) Ultrastructure of chloroplasts and mitochondria in line RNAi-5. (G) Chloroplast ultrastructure in the weakest RNAi line (RNAi-12). Scale bars: 1 μm.
Mentions: To assess the consequences of PRORP1 suppression at the ultrastructural level, chloroplasts and mitochondria were analyzed by transmission electron microscopy (Fig. 3). Conspicuous changes were seen in both chloroplast and mitochondrial ultrastructure, which were most pronounced in the strongest RNAi line, RNAi-2. Chloroplasts were smaller than in wild-type cells and displayed a somewhat more intense stacking of grana thylakoids. This observation is in line with the chlorophyll a:b ratio being decreased in the mutants (2.43±0.13 in the wild type versus 2.16±0.17 in line RNAi-2; Fig. 1E), which was found to correlate with increased grana stacking also in other mutants with impaired chloroplast function [42]. Mitochondrial shape was also altered in the PRORP1 RNAi lines. Whereas, in wild-type cells, mitochondria were round or oval, they were bigger and much more elongated in the mutants, especially in cells of the RNAi-2 line (Fig. 3). In contrast to the previously reported transient repression of PRORP1 (by virus-induced gene silencing; [8]), we did not observe “dense mitochondrial structures containing vacuoles”. Whether this alteration in mitochondrial morphology represents a direct compensatory response to impaired mitochondrial gene expression or rather an indirect consequence of disturbed chloroplast function in the RNAi mutants, remains to be determined.

Bottom Line: PRORP1 knock-down lines show defects in photosynthesis, while mitochondrial respiration is not appreciably affected.In both plastids and mitochondria, the effects of PRORP1 knock-down on the processing of individual tRNA species are highly variable.The drastic reduction in the levels of mature plastid tRNA-Phe(GAA) and tRNA-Arg(ACG) suggests that these two tRNA species limit plastid gene expression in the PRORP1 mutants and, hence, are causally responsible for the mutant phenotype.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Potsdam-Golm, Germany.

ABSTRACT
Transfer RNA (tRNA) precursors undergo endoribonucleolytic processing of their 5' and 3' ends. 5' cleavage of the precursor transcript is performed by ribonuclease P (RNase P). While in most organisms RNase P is a ribonucleoprotein that harbors a catalytically active RNA component, human mitochondria and the chloroplasts (plastids) and mitochondria of seed plants possess protein-only RNase P enzymes (PRORPs). The plant organellar PRORP (PRORP1) has been characterized to some extent in vitro and by transient gene silencing, but the molecular, phenotypic and physiological consequences of its down-regulation in stable transgenic plants have not been assessed. Here we have addressed the function of the dually targeted organellar PRORP enzyme in vivo by generating stably transformed Arabidopsis plants in which expression of the PRORP1 gene was suppressed by RNA interference (RNAi). PRORP1 knock-down lines show defects in photosynthesis, while mitochondrial respiration is not appreciably affected. In both plastids and mitochondria, the effects of PRORP1 knock-down on the processing of individual tRNA species are highly variable. The drastic reduction in the levels of mature plastid tRNA-Phe(GAA) and tRNA-Arg(ACG) suggests that these two tRNA species limit plastid gene expression in the PRORP1 mutants and, hence, are causally responsible for the mutant phenotype.

No MeSH data available.


Related in: MedlinePlus