Synthesis of the D1 reaction center protein of Photosystem II is dynamically regulated in response to environmental and developmental cues. In chloroplasts, much of this regulation occurs at the post‐transcriptional level, but the proteins responsible are largely unknown. To discover proteins that impact
The D1 reaction center protein of photosystem II (PSII) is subject to light-induced damage. Degradation of damaged D1 and its replacement by nascent D1 are at the heart of a PSII repair cycle, without which photosynthesis is inhibited. In mature plant chloroplasts, light stimulates the recruitment of ribosomes specifically to
- NSF-PAR ID:
- 10184880
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 35
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 21775-21784
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Summary psbA expression, we identified proteins that associate with maizepsbA mRNA by: (i) formaldehyde cross‐linking of leaf tissue followed by antisense oligonucleotide affinity capture ofpsbA mRNA; and (ii) co‐immunoprecipitation with HCF173, apsbA translational activator that is known to bindpsbA mRNA. The S1 domain protein SRRP1 and two RNA Recognition Motif (RRM) domain proteins, CP33C and CP33B, were enriched with both approaches. Orthologous proteins were also among the enriched protein set in a previous study in Arabidopsis that employed a designer RNA‐binding protein as apsbA RNA affinity tag. We show here that CP33B is bound topsbA mRNAin vivo, as was shown previously for CP33C and SRRP1. Immunoblot, pulse labeling, and ribosome profiling analyses of mutants lacking CP33B and/or CP33C detected some decreases in D1 protein levels under some conditions, but no change inpsbA RNA abundance or translation. However, analogous experiments showed that SRRP1 repressespsbA ribosome association in the dark, repressesycf1 ribosome association, and promotes accumulation ofndhC mRNA. As SRRP1 is known to harbor RNA chaperone activity, we postulate that SRRP1 mediates these effects by modulating RNA structures. The uncharacterized proteins that emerged from our analyses provide a resource for the discovery of proteins that impact the expression ofpsbA and other chloroplast genes. -
Summary The expression of chloroplast genes relies on a host of nucleus‐encoded proteins. Identification of such proteins and elucidation of their functions are ongoing challenges. We used ribosome profiling to revisit the function of the pentatricopeptide repeat protein LPE1, reported to stimulate translation of the chloroplast
psbA mRNA in Arabidopsis. Mutation of the maizeLPE1 ortholog causes a photosystem II (PSII) deficiency and a defect in translation of the chloroplastpsbJ open reading frame (ORF) but has no effect onpsbA expression. To reflect this function, we named the maize LPE1 orthologT ranslation ofp sb 1 (TPJ1). ArabidopsisJ lpe1 mutants likewise exhibit a loss ofpsbJ translation, and have, in addition, a decrease inpsbN translation. We detected a small decrease in ribosome occupancy on thepsbA mRNA in Arabidopsislpe1 mutants, but ribosome profiling analyses of other PSII mutants (hcf107 andhcf173 ) in conjunction within vitro RNA binding data strongly suggest that this is a secondary effect of their PSII deficiency. We conclude that maize TPJ1 promotes PSII synthesis by activating translation of thepsbJ ORF, that this function is conserved in Arabidopsis LPE1, and that an additional role for LPE1 inpsbN translation contributes to the PSII deficiency inlpe1 mutants. -
Iron (Fe) is an essential micronutrient whose availability is limiting in many soils. During Fe deficiency, plants alter the expression of many genes to increase Fe uptake, distribution, and utilization. In a genetic screen for suppressors of Fe sensitivity in the E3 ligase mutant
bts-3 , we isolated an allele of the bHLH transcription factor (TF)ILR3 ,ilr3-4 . We identified a striking leaf bleaching phenotype inilr3 mutants that was suppressed by limiting light intensity, indicating that ILR3 is required for phototolerance during Fe deficiency. Among its paralogs that are thought to be partially redundant, onlyILR3 was required for phototolerance as well as repression of genes under Fe deficiency. A mutation in the gene-encoding PYE, a known transcriptional repressor under Fe deficiency, also caused leaf bleaching. We identified singlet oxygen as the accumulating reactive oxygen species (ROS) inilr3-4 andpye , suggesting photosensitivity is due to a PSII defect resulting in ROS production. During Fe deficiency,ilr3-4 andpye chloroplasts retain normal ultrastructure and, unlike wild type (WT), contain stacked grana similar to Fe-sufficient plants. Additionally, we found that the D1 subunit of PSII is destabilized in WT during Fe deficiency but not inilr3-4 andpye , suggesting that PSII repair is accelerated during Fe deficiency in an ILR3- and PYE-dependent manner. Collectively, our results indicate that ILR3 and PYE confer photoprotection during Fe deficiency to prevent the accumulation of singlet oxygen, potentially by promoting reduction of grana stacking to limit excitation and facilitate repair of the photosynthetic machinery. -
Premise Light is critical in the ability of plants to accumulate chlorophyll. When exposed to far‐red (
FR ) light and then grown in white light in the absence of sucrose, wild‐type seedlings fail to green in a response known as theFR block of greening (BOG ). This response is controlled by phytochrome A through repression of protochlorophyllide reductase‐encoding (POR ) genes byFR light coupled with irreversible plastid damage. Sigma (SIG ) factors are nuclear‐encoded proteins that contribute to plant greening and plastid development through regulating gene transcription in chloroplasts and impacting retrograde signaling from the plastid to nucleus.SIG s are regulated by phytochromes, and the expression of someSIG factors is reduced in phytochrome mutant lines, includingphyA . Given the association of phyA with theFR BOG and its regulation ofSIG factors, we investigated the potential regulatory role ofSIG factors in theFR BOG response.Methods We examined
FR BOG responses insig mutants, phytochrome‐deficient lines, and mutant lines for several phy‐associated factors. We quantified chlorophyll levels and examined expression of keyBOG ‐associated genes.Results Among six
sig mutants, only thesig6 mutant significantly accumulated chlorophyll afterFR BOG treatment, similar to thephyA mutant.SIG 6 appears to control protochlorophyllide accumulation by contributing to the regulation of tetrapyrrole biosynthesis associated with glutamyl‐tRNA reductase (HEMA 1) function, select phytochrome‐interacting factor genes (PIF4 andPIF6 ), andPENTA1 , which regulatesPORA mRNA translation afterFR exposure.Conclusions Regulation of
SIG6 plays a significant role in plant responses toFR exposure during theBOG response. -
Allard, Jun (Ed.)For many nuclear-encoded mitochondrial genes, mRNA localizes to the mitochondrial surface co-translationally, aided by the association of a mitochondrial targeting sequence (MTS) on the nascent peptide with the mitochondrial import complex. For a subset of these co-translationally localized mRNAs, their localization is dependent on the metabolic state of the cell, while others are constitutively localized. To explore the differences between these two mRNA types we developed a stochastic, quantitative model for MTS-mediated mRNA localization to mitochondria in yeast cells. This model includes translation, applying gene-specific kinetics derived from experimental data; and diffusion in the cytosol. Even though both mRNA types are co-translationally localized we found that the steady state number, or density, of ribosomes along an mRNA was insufficient to differentiate the two mRNA types. Instead, conditionally-localized mRNAs have faster translation kinetics which modulate localization in combination with changes to diffusive search kinetics across metabolic states. Our model also suggests that the MTS requires a maturation time to become competent to bind mitochondria. Our work indicates that yeast cells can regulate mRNA localization to mitochondria by controlling mitochondrial volume fraction (influencing diffusive search times) and gene translation kinetics (adjusting mRNA binding competence) without the need for mRNA-specific binding proteins. These results shed light on both global and gene-specific mechanisms that enable cells to alter mRNA localization in response to changing metabolic conditions.more » « less