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. 2020 Aug;183(4):1438-1452.
doi: 10.1104/pp.20.00076. Epub 2020 Jun 8.

Organellar and Secretory Ribonucleases: Major Players in Plant RNA Homeostasis

Gustavo C MacIntosh  1 , Benoît Castandet  2   3
Affiliations

Organellar and Secretory Ribonucleases: Major Players in Plant RNA Homeostasis

Gustavo C MacIntosh et al. Plant Physiol. 2020 Aug.

Abstract

Organellar and secretory RNases, associated with different cellular compartments, are essential to maintain cellular homeostasis during development and in stress responses.

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Figures

Figure 1.
Figure 1.
The roles of ribonucleases in chloroplast and mitochondrial mRNA metabolism. A, (i) In chloroplasts, RNase J processes the 5′ end of polycistronic mRNAs, whereas PNPase and RNR1 cooperatively mature the 3′ ends. The transcript is also subject to intercistronic cleavage by several endoribonucleases, but the division of labor between RNase J, RNase E, and CSP41 is unclear. A, (ii) Another round of exoribonuclease digestion gives the final termini. Mature transcript ends are protected from exoribonuclease degradation by sequence-specific RNA binding proteins (for example, PPR proteins) and secondary structures. A, (iii) Illegitimate, partially, or misprocessed transcripts are then digested at the 3′ end by PNPase following the addition of a poly(A) tail. RNase J also participates in RNA degradation and surveillance. Its major role preventing the formation of double stranded RNA is not represented. B, (i) In mitochondria, endoribonucleases have a major role in defining 5′ ends through their interactions with PPR proteins that specifically bind RNA targets. Cleavage by PRORP1, MNU1/2, or yet unknown endoribonucleases occurs downstream of the PPR binding site. Alternatively, PRORP1 and TRZ3/4 can cleave tRNAs or t-elements between two genes and release mature or intermediate 5′ and 3′ ends. As in chloroplasts, PNPase and RNR1 cooperatively mature the 3′ ends. B, (ii) Mature 3′ ends are protected from exoribonuclease degradation by RBPs and/or secondary structures. B, (iii) Illegitimate, partially, or misprocessed transcripts are then digested at the 3′ end by PNPase, following the addition of a poly(A) tail. Additionally, the 3′-5′ exoribonuclease PARN appears to regulate the poly(A) status of correctly processed transcripts; however, the significance of this activity is unclear. RNase, RNase; PNPase, polynucleotide phosphorylase; RNR1, RNase R homolog 1; CSP41, chloroplast stem loop binding protein of 41 kD; PRORP1, PROTEINACEOUS RNASE P1; MNU, mitochondrial nuclease; TRZ, RNase Z; RBP, RNA binding protein;. Figure inspired by Germain et al. (2013).
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