Epyrifenacil, a new systemic PPO-inhibiting herbicide for broad-spectrum weed control.

Epyrifenacil is a novel PPO-inhibiting herbicide discovered and developed by Sumitomo Chemical. Epyrifenacil belongs to the pyrimidinedione chemical class and has a unique three-ring structure. It is systemically active on a broad range of weeds including grass weeds and some target-site-based PPO-inhibitor resistant broadleaf weeds. Its systemic action is mediated by a phloem movement of the active form of epyrifenacil. In addition, epyrifenacil's vapor action is sufficiently low to not cause an off-target movement to nontarget sensitive crops. It is expected that epyrifenacil will contribute to global food production in the near future. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Physiological effects of mandestrobin.

Mandestrobin is a novel and potent fungicide with a methoxyacetamide structure, and inhibits complex III on the mitochondrial respiratory chain of fungi. It is widely accepted that some fungicides, including QOIs and SDHIs, have additional physiological effects on treated plants. In this study, we evaluated the physiological effects of mandestrobin both in the field and the laboratory. Mandestrobin treatment increased the yield of Brassica napus by an average of 6.3% in the field under disease-free conditions. Mandestrobin treatment delayed chlorophyll degradation and the senescence of B. napus leaf discs, and excised Arabidopsis thaliana leaves in darkness. Analyses of transcriptome and gene ontology enrichment of mandestrobin-upregulated genes showed that chlorophyll degradation genes and jasmonate-related genes were downregulated while salicylate-related genes were upregulated by mandestrobin treatment. A possible mechanism by which mandestrobin triggered the physiological effects observed in the field and the laboratory was discussed.

Cross-linking evidence for multiple interactions of the PsbP and PsbQ proteins in a higher plant photosystem II supercomplex.

The extrinsic subunits of membrane-bound photosystem II (PSII) maintain an essential role in optimizing the water-splitting reaction of the oxygen-evolving complex (OEC), even though they have undergone drastic change during the evolution of oxyphototrophs from symbiotic cyanobacteria to chloroplasts. Two specific extrinsic proteins, PsbP and PsbQ, bind to the lumenal surface of PSII in green plants and maintain OEC conformation and stabilize overall enzymatic function; however, their precise location has not been fully resolved. In this study, PSII-enriched membranes, isolated from spinach, were subjected to chemical cross-linking combined with release-reconstitution experiments. We observed direct interactions between PsbP and PsbE, as well as with PsbR. Intriguingly, PsbP and PsbQ were further linked to the CP26 and CP43 light-harvesting proteins. In addition, two cross-linked sites, between PsbP and PsbR, and that of PsbP and CP26, were identified by tandem mass spectrometry. These data were used to estimate the binding topology and location of PsbP, and the putative positioning of PsbQ and PsbR on the lumenal surface of the PSII. Our model gives new insights into the organization of PSII extrinsic subunits in higher plants and their function in stabilizing the OEC of the PSII supercomplex.

Identification of the basic amino acid residues on the PsbP protein involved in the electrostatic interaction with photosystem II.

The PsbP protein is an extrinsic subunit of photosystem II (PSII) that is essential for photoautotrophic growth in higher plants. Several crystal structures of PsbP have been reported, but the binding topology of PsbP in PSII has not yet been clarified. In this study, we report that the basic pocket of PsbP, which consists of conserved Arg48, Lys143, and Lys160, is important for the electrostatic interaction with the PSII complex. Our release-reconstitution experiment showed that the binding affinities of PsbP-R48A, -K143A, and -K160A mutated proteins to PSII were lower than that of PsbP-WT, and triple mutations of these residues greatly diminished the binding affinity to PSII. Even when maximum possible binding had occurred, the R48A, K143A, and K160A proteins showed a reduced ability to restore the rate of oxygen evolution at low chloride concentrations. Fourier transform infrared resonance (FTIR) difference spectroscopy results were consistent with the above finding, and suggested that these mutated proteins were not able to induce the normal conformational change around the Mn cluster during S1 to S2 transition. Finally, chemical cross-linking experiments suggested that the interaction between the N-terminus of PsbP with PsbE was inhibited by these mutations. These data suggest that the basic pocket of PsbP is important for proper association and interaction with PSII. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

The conserved His-144 in the PsbP protein is important for the interaction between the PsbP N-terminus and the Cyt b559 subunit of photosystem II.

The PsbP protein regulates the binding properties of Ca(2+) and Cl(-), and stabilizes the Mn cluster of photosystem II (PSII); however, the binding site and topology in PSII have yet to be clarified. Here we report that the structure around His-144 and Asp-165 in PsbP, which is suggested to be a metal binding site, has a crucial role for the functional interaction between PsbP and PSII. The mutated PsbP-H144A protein exhibits reduced ability to retain Cl(-) anions in PSII, whereas the D165V mutation does not affect PsbP function. Interestingly, H144A/D165V double mutation suppresses the effect of H144A mutation, suggesting that these residues have a role other than metal binding. FTIR difference spectroscopy suggests that H144A/D165V restores proper interaction with PSII and induces the conformational change around the Mn cluster during the S(1)/S(2) transition. Cross-linking experiments show that the H144A mutation affects the direct interaction between PsbP and the Cyt b(559) α subunit of PSII (the PsbE protein). However, this interaction is restored in the H144A/D165V mutant. In the PsbP structure, His-144 and Asp-165 form a salt bridge. H144A mutation is likely to disrupt this bridge and liberate Asp-165, inhibiting the proper PsbP-PSII interaction. Finally, mass spectrometric analysis has identified the cross-linked sites of PsbP and PsbE as Ala-1 and Glu-57, respectively. Therefore His-144, in the C-terminal domain of PsbP, plays a crucial role in maintaining proper N terminus interaction. These data provide important information about the binding characteristics of PsbP in green plant PSII.

The PsbQ protein stabilizes the functional binding of the PsbP protein to photosystem II in higher plants.

PsbP and PsbQ proteins are extrinsic subunits of photosystem II (PSII) and optimize the oxygen evolution reaction by regulating the binding properties of the essential cofactors Ca(2+) and Cl(-). PsbP induces conformational changes around the catalytic Mn cluster required for Ca(2+) and Cl(-) retention, and the N-terminal region of PsbP is essential for this reaction. It was reported that PsbQ partially restores the functional defect of N-terminal truncated PsbP [Ifuku and Sato (2002) Plant Cell Physiol. 43, 1244-1249]; however, the mechanism of this restoration is yet to be clarified. In this study, we demonstrate that PsbQ is able to restore the functional binding of mutated PsbPs. In the presence of PsbQ, ∆15-PsbP, a truncated PsbP lacking 15 N-terminal residues, was able to specifically bind to NaCl-washed spinach PSII membranes and significantly restore the oxygen evolving activity. Furthermore, PsbQ was also able to compensate for the impaired ion-retention of H144A-PsbP, in which a conserved histidine at position 144 in the C-terminal domain was substituted with an alanine. Fourier transform infrared (FTIR) difference spectroscopy showed that PsbQ restored the ability of ∆15- and H144A-PsbP to induce proper conformational changes during S(1) to S(2) transition. These data suggest that the major function of PsbQ is to stabilize PsbP binding, thereby contributing to the maintenance of the catalytic Mn cluster of the water oxidation machinery in higher plant PSII. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Molecular functions of PsbP and PsbQ proteins in the photosystem II supercomplex.

The PsbP and PsbQ proteins are extrinsic subunits of the photosystem II (PSII) supercomplex, which are found in green plants including higher plants and green algae. These proteins are thought to have evolved from their cyanobacterial homologs; cyanoP and cyanoQ respectively. It has been suggested that the functions of PsbP and PsbQ have largely changed from those of cyanoP and cyanoQ. In addition, multiple isoforms and homologs of PsbP and PsbQ were found in green plants, indicating that the acquisition of PsbP and PsbQ in PSII is not a direct path but a result of intensive functional divergence during evolution from cyanobacterial endosymbiont to chloroplast. In this review, we highlight newly introduced topics related to the functions and structures of both PsbP and PsbQ proteins. The present data suggest that PsbP together with PsbQ have specific and important roles in coordinating the activity of the donor and acceptor sides of PSII and stabilizing the active form of the PSII-light-harvesting complex II (LHCII) supercomplex.

High and low potential forms of the QA quinone electron acceptor in Photosystem II of Thermosynechococcus elongatus and spinach.

The redox potential of Q(A) in Photosystem II (PSII) from Thermosynechococcus elongatus was titrated monitoring chlorophyll fluorescence. A high potential form (E(m)=+60 ± 25 mV) was found in the absence of Mn(4)Ca, the active site for water oxidation. The low potential form (E(m)=-60 ± 48 mV), which is difficult to measure in conventional titration experiments, could be "locked in" by cross-linking the active enzyme. This indicates that the presence of Mn(4)Ca is relayed to the quinone site by significant structural changes in the protein. The presence of high and low potential forms agrees with what has been seen in plants, algae from our lab and in T. elongatus (Shibamoto et al., Biochemistry 48 (2009) 10682-10684). In the latter work, the potentials of Q(A) were shifted to lower potentials compared to other measurements. The redox potential of Q(A) in Mn-depleted PSII from spinach was titrated in the presence of redox mediators and the midpoint potential was shifted by 80 mV towards a more negative value compared to titrations without mediators. The lower values of the midpoint potential of the (Q(A)/Q(A)(-)) redox couple in the literature could be due to a perturbation due to a specific mediator.

Three PsbQ-like proteins are required for the function of the chloroplast NAD(P)H dehydrogenase complex in Arabidopsis.

Arabidopsis has three PsbQ-like (PQL) proteins in addition to the PsbQ subunit of the oxygen-evolving complex of PSII. Recent bioinformatic and proteomic studies suggested that the two PQL proteins, PQL1 (At1g14150) and PQL2 (At3g01440), might function in the chloroplast NAD(P)H dehydrogenase (NDH) complex; however, their molecular function has not been characterized. In this study, we examined the function of the chloroplast NDH in the Arabidopsis pql1 and pql2 mutants. Post-illumination increases in Chl fluorescence, which are caused by an NDH-dependent cyclic electron flow, were absent in both mutants, indicating that PQL1 and PQL2 are required for NDH activity. In the thylakoid membranes of wild-type plants, PQL1 and PQL2 were tightly associated with the NDH-PSI supercomplex and protected from protease treatments, while unassembled PQLs were not stably accumulated in mutants lacking known NDH subunits. Subunit stability of the NDH complex was affected differently in the thylakoid membranes of the pql1 and pql2 mutants. These data indicate that PQL1 and PQL2 are novel NDH subunits and differ in their functional roles and in their binding sites in the NDH complex. Furthermore, functional analysis on PQL3 (At2g01918) using the pql3 mutant suggests that PQL3 is also required for NDH activity. Proteins homologous to each PQL protein are found in various plant species, but not in cyanobacteria, algae, mosses or ferns. These results suggest that seed plants that have NDH activity in chloroplasts specifically developed three PQL proteins for the function of the chloroplast NDH complex.

The variegated mutants lacking chloroplastic FtsHs are defective in D1 degradation and accumulate reactive oxygen species.

In the photosynthetic apparatus, a major target of photodamage is the D1 reaction center protein of photosystem II (PSII). Photosynthetic organisms have developed a PSII repair cycle in which photodamaged D1 is selectively degraded. A thylakoid membrane-bound metalloprotease, FtsH, was shown to play a critical role in this process. Here, the effect of FtsHs in D1 degradation was investigated in Arabidopsis (Arabidopsis thaliana) mutants lacking FtsH2 (yellow variegated2 [var2]) or FtsH5 (var1). Because these mutants are characterized by variegated leaves that sometimes complicate biochemical studies, we employed another mutation, fu-gaeri1 (fug1), that suppresses leaf variegation in var1 and var2 to examine D1 degradation. Two-dimensional blue native PAGE showed that var2 has less PSII supercomplex and more PSII intermediate lacking CP43, termed RC47, than the wild type under normal growth light. Moreover, our histochemical and quantitative analyses revealed that chloroplasts in var2 accumulate significant levels of reactive oxygen species, such as superoxide radical and hydrogen peroxide. These results indicate that the lack of FtsH2 leads to impaired D1 degradation at the step of RC47 formation in PSII repair and to photooxidative stress even under nonphotoinhibitory conditions. Our in vivo D1 degradation assays, carried out by nonvariegated var2 fug1 and var1 fug1 leaves, demonstrated that D1 degradation was impaired in different light conditions. Taken together, our results suggest the important role of chloroplastic FtsHs, which was not precisely examined in vivo. Attenuated D1 degradation in the nonvariegated mutants also suggests that leaf variegation seems to be independent of the PSII repair.

Knockdown of the PsbP protein does not prevent assembly of the dimeric PSII core complex but impairs accumulation of photosystem II supercomplexes in tobacco.

The PsbP protein is an extrinsic subunit of photosystem II (PSII) specifically found in land plants and green algae. Using PsbP-RNAi tobacco, we have investigated effects of PsbP knockdown on protein supercomplex organization within the thylakoid membranes and photosynthetic properties of PSII. In PsbP-RNAi leaves, PSII dimers binding the extrinsic PsbO protein could be formed, while the light-harvesting complex II (LHCII)-PSII supercomplexes were severely decreased. Furthermore, LHCII and major PSII subunits were significantly dephosphorylated. Electron microscopic analysis showed that thylakoid grana stacking in PsbP-RNAi chloroplast was largely disordered and appeared similar to the stromally-exposed or marginal regions of wild-type thylakoids. Knockdown of PsbP modified both the donor and acceptor sides of PSII; In addition to the lower water-splitting activity, the primary quinone Q(A) in PSII was significantly reduced even when the photosystem I reaction center (P700) was noticeably oxidized, and thermoluminescence studies suggested the stabilization of the charged pair, S(2)/Q(A)(-). These data indicate that assembly and/or maintenance of the functional MnCa cluster is perturbed in absence of PsbP, which impairs accumulation of final active forms of PSII supercomplexes.

Structure, function, and evolution of the PsbP protein family in higher plants.

The PsbP is a thylakoid lumenal subunit of photosystem II (PSII), which has developed specifically in higher plants and green algae. In higher plants, the molecular function of PsbP has been intensively investigated by release-reconstitution experiments in vitro. Recently, solution of a high-resolution structure of PsbP has enabled investigation of structure-function relationships, and efficient gene-silencing techniques have demonstrated the crucial role of PsbP in PSII activity in vivo. Furthermore, genomic and proteomic studies have shown that PsbP belongs to the divergent PsbP protein family, which consists of about 10 members in model plants such as Arabidopsis and rice. Characterization of the molecular function of PsbP homologs using Arabidopsis mutants suggests that each plays a distinct and important function in maintaining photosynthetic electron transfer. In this review, recent findings regarding the molecular functions of PsbP and other PsbP homologs in higher plants are summarized, and the molecular evolution of these proteins is discussed.

Distinct functions for the two PsbP-like proteins PPL1 and PPL2 in the chloroplast thylakoid lumen of Arabidopsis.

PsbP, an extrinsic subunit of photosystem II (PSII), is a nuclear-encoded protein that optimizes the water-splitting reaction in vivo. In addition to PsbP, higher plants have two nuclear-encoded genes for PsbP homologs (PsbP-like proteins [PPLs]) that show significant sequence similarity to a cyanobacterial PsbP homolog (cyanoP); however, the function of PPLs in higher plants has not yet been elucidated. In this study, we characterized Arabidopsis (Arabidopsis thaliana) mutants lacking either of two PPLs, PPL1 and PPL2. Phylogenetic analysis suggests that PPL1 would be an ortholog of cyanoP, and PPL2 and PsbP may have a paralogous relationship with PPL1. Analysis on mRNA expression profiles showed that PPL1 expressed under stress conditions and PPL2 coexpressed with the subunits of chloroplast NAD(P)H dehydrogenase (NDH) complex. Consistent with these suggestions, PSII activity in a ppl1 mutant was more sensitive to high-intensity light than wild type, and the recovery of photoinhibited PSII activity was delayed in ppl1 plants. Therefore, PPL1 is required for efficient repair of photodamaged PSII. Furthermore, the stoichiometric level and activity of the chloroplast NDH complex in thylakoids were severely decreased in a ppl2 mutant, demonstrating that PPL2 is a novel thylakoid lumenal factor required for accumulation of the chloroplast NDH complex. These results suggest that during endosymbiosis and subsequent gene transfer to the host nucleus, cyanoP from ancient cyanobacteria evolved into PPL1, PPL2, and PsbP, and each of them has a distinct role in photosynthetic electron transfer in Arabidopsis.