Structural basis of jasmonate-amido synthetase FIN219 in complex with glutathione S-transferase FIP1 during the JA signal regulation

Chemical genetic screening identifies nalacin as an inhibitor of GH3 amido synthetase for auxin conjugation

Auxin inactivation is critical for plant growth and development. To develop plant growth regulators functioning in auxin inactivation pathway, we performed a phenotype-based chemical screen in Arabidopsis and identified a chemical, nalacin, that partially mimicked the effects of auxin. Genetic, pharmacological, and biochemical approaches demonstrated that nalacin exerts its auxin-like activities by inhibiting indole-3-acetic acid (IAA) conjugation that is mediated by Gretchen Hagen 3 (GH3) acyl acid amido synthetases. The crystal structure of Arabidopsis GH3.6 in complex with D4 (a derivative of nalacin) together with docking simulation analysis revealed the molecular basis of the inhibition of group II GH3 by nalacin. Sequence alignment analysis indicated broad bioactivities of nalacin and D4 as inhibitors of GH3s in vascular plants, which were confirmed, at least, in tomato and rice. In summary, our work identifies nalacin as a potent inhibitor of IAA conjugation mediated by group II GH3 that plays versatile roles in hormone-regulated plant development and has potential applications in both basic research and agriculture.

The Shared Proteome of the Apomictic Fern Dryopteris affinis ssp. affinis and Its Sexual Relative Dryopteris oreades

Ferns are a diverse evolutionary lineage, sister to the seed plants, which is of great ecological importance and has a high biotechnological potential. Fern gametophytes represent one of the simplest autotrophic, multicellular plant forms and show several experimental advantages, including a simple and space-efficient in vitro culture system. However, the molecular basis of fern growth and development has hardly been studied. Here, we report on a proteomic study that identified 417 proteins shared by gametophytes of the apogamous fern Dryopteris affinis ssp. affinis and its sexual relative Dryopteris oreades. Most proteins are predicted to localize to the cytoplasm, the chloroplast, or the nucleus, and are linked to enzymatic, binding, and structural activities. A subset of 145 proteins are involved in growth, reproduction, phytohormone signaling and biosynthesis, and gene expression, including homologs of SHEPHERD (SHD), HEAT SHOCK PROTEIN 90-5 (CR88), TRP4, BOBBER 1 (BOB1), FLAVONE 3'-O-METHYLTRANSFERASE 1 (OMT1), ZEAXANTHIN EPOXIDASE (ABA1), GLUTAMATE DESCARBOXYLASE 1 (GAD), and dsRNA-BINDING DOMAIN-LIKE SUPERFAMILY PROTEIN (HLY1). Nearly 25% of the annotated proteins are associated with responses to biotic and abiotic stimuli. As for biotic stress, the proteins PROTEIN SGT1 HOMOLOG B (SGT1B), SUPPRESSOR OF SA INSENSITIVE2 (SSI2), PHOSPHOLIPASE D ALPHA 1 (PLDALPHA1), SERINE/THREONINE-PROTEIN KINASE SRK2E (OST1), ACYL CARRIER PROTEIN 4 (ACP4), and NONHOST RESISTANCE TO P. S. PHASEOLICOLA1 (GLPK) are worth mentioning. Regarding abiotic stimuli, we found proteins associated with oxidative stress: SUPEROXIDE DISMUTASE[CU-ZN] 1 (CSD1), and GLUTATHIONE S-TRANSFERASE U19 (GSTU19), light intensity SERINE HYDROXYMETHYLTRANSFERASE 1 (SHM1) and UBIQUITIN-CONJUGATING ENZYME E2 35 (UBC35), salt and heavy metal stress included MITOCHONDRIAL PHOSPHATE CARRIER PROTEIN 3 (PHT3;1), as well as drought and thermotolerance: LEA7, DEAD-BOX ATP-DEPENDENT RNA HELICASE 38 (LOS4), and abundant heat-shock proteins and other chaperones. In addition, we identified interactomes using the STRING platform, revealing protein-protein associations obtained from co-expression, co-occurrence, text mining, homology, databases, and experimental datasets. By focusing on ferns, this proteomic study increases our knowledge on plant development and evolution, and may inspire future applications in crop species.

Biochemical and Structural Insights on the Poplar Tau Glutathione Transferase GSTU19 and 20 Paralogs Binding Flavonoids

Glutathione transferases (GSTs) constitute a widespread superfamily of enzymes notably involved in xenobiotic detoxification and/or in specialized metabolism. Populus trichocarpa genome (V4.1 assembly, Phytozome 13) consists of 74 genes coding for full-length GSTs and ten likely pseudogenes. These GSTs are divided into 11 classes, in which the tau class (GSTU) is the most abundant with 54 isoforms. PtGSTU19 and 20, two paralogs sharing more than 91% sequence identity (95% of sequence similarity), would have diverged from a common ancestor of P. trichocarpa and P. yatungensis species. These enzymes display the distinctive glutathione (GSH)-conjugation and peroxidase activities against model substrates. The resolution of the crystal structures of these proteins revealed significant structural differences despite their high sequence identity. PtGSTU20 has a well-defined deep pocket in the active site whereas the bottom of this pocket is disordered in PtGSTU19. In a screen of potential ligands, we were able to identify an interaction with flavonoids. Some of them, previously identified in poplar (chrysin, galangin, and pinocembrin), inhibited GSH-conjugation activity of both enzymes with a more pronounced effect on PtGSTU20. The crystal structures of PtGSTU20 complexed with these molecules provide evidence for their potential involvement in flavonoid transport in P. trichocarpa.

Sexual and Apogamous Species of Woodferns Show Different Protein and Phytohormone Profiles

The gametophyte of ferns reproduces either by sexual or asexual means. In the latter, apogamy represents a peculiar case of apomixis, in which an embryo is formed from somatic cells. A proteomic and physiological approach was applied to the apogamous fern Dryopteris affinis ssp. affinis and its sexual relative D. oreades. The proteomic analysis compared apogamous vs. female gametophytes, whereas the phytohormone study included, in addition to females, three apogamous stages (filamentous, spatulate, and cordate). The proteomic profiles revealed a total of 879 proteins and, after annotation, different regulation was found in 206 proteins of D. affinis and 166 of its sexual counterpart. The proteins upregulated in D. affinis are mostly associated to protein metabolism (including folding, transport, and proteolysis), ribosome biogenesis, gene expression and translation, while in the sexual counterpart, they account largely for starch and sucrose metabolism, generation of energy and photosynthesis. Likewise, ultra-performance liquid chromatography-tandem spectrometry (UHPLC-MS/MS) was used to assess the levels of indol-3-acetic acid (IAA); the cytokinins: 6-benzylaminopurine (BA), trans-Zeatine (Z), trans-Zeatin riboside (ZR), dyhidrozeatine (DHZ), dyhidrozeatin riboside (DHZR), isopentenyl adenine (iP), isopentenyl adenosine (iPR), abscisic acid (ABA), the gibberellins GA₃ and GA₄, salicylic acid (SA), and the brassinosteroids: brassinolide (BL) and castasterone (CS). IAA, the cytokinins Z, ZR, iPR, the gibberellin GA₄, the brassinosteoids castasterone, and ABA accumulated more in the sexual gametophyte than in the apogamous one. When comparing the three apogamous stages, BA and SA peaked in filamentous, GA₃ and BL in spatulate and DHRZ in cordate gametophytes. The results point to the existence of large metabolic differences between apogamous and sexual gametophytes, and invite to consider the fern gametophyte as a good experimental system to deepen our understanding of plant reproduction.

LEDs Make It Resilient: Effects on Plant Growth and Defense

Light spectral composition influences plant growth and metabolism, and has important consequences for interactions with plant-feeding arthropods and their natural enemies. In greenhouse horticulture, light spectral composition can be precisely manipulated by light-emitting diodes (LEDs), and LEDs are already used to optimize crop production and quality. However, because light quality also modulates plant secondary metabolism and defense, it is important to understand the underlying mechanisms in the context of the growth-defense trade-off. We review the effects of the spectral composition of supplemental light currently used, or potentially used, in greenhouse horticulture on the mechanisms underlying plant growth and defense. This information is important for exploring opportunities to optimize crop performance and pest management, and thus for developing resilient crop-production systems.

Genome sequencing and population genomics modeling provide insights into the local adaptation of weeping forsythia

Understanding the genetic basis underlying the local adaptation of nonmodel species is a fundamental goal in evolutionary biology. In this study, we explored the genetic mechanisms of the local adaptation of Forsythia suspensa using genome sequence and population genomics data obtained from specific-locus amplified fragment sequencing. We assembled a high-quality reference genome of weeping forsythia (Scaffold N50 = 7.3 Mb) using ultralong Nanopore reads. Then, genome-wide comparative analysis was performed for 15 natural populations of weeping forsythia across its current distribution range. Our results revealed that candidate genes associated with local adaptation are functionally correlated with solar radiation, temperature and water variables across heterogeneous environmental scenarios. In particular, solar radiation during the period of fruit development and seed drying after ripening, cold, and drought significantly contributed to the adaptive differentiation of F. suspensa. Natural selection exerted by environmental factors contributed substantially to the population genetic structure of F. suspensa. Our results supported the hypothesis that adaptive differentiation should be highly pronounced in the genes involved in signal crosstalk between different environmental variables. Our population genomics study of F. suspensa provides insights into the fundamental genetic mechanisms of the local adaptation of plant species to climatic gradients.

In Vitro Analytical Approaches to Study Plant Ligand-Receptor Interactions

State-of-the-art in vitro methods characterize receptor-ligand interactions, highlighting experiment strategies, advantages and limitations.

GSTU43 gene involved in ALA-regulated redox homeostasis, to maintain coordinated chlorophyll synthesis of tomato at low temperature

BACKGROUND

Exogenous 5-aminolevulinic acid (ALA) positively regulates plants chlorophyll synthesis and protects them against environmental stresses, although the protection mechanism is not fully clear. Here, we explored the effects of ALA on chlorophyll synthesis in tomato plants, which are sensitive to low temperature. We also examined the roles of the glutathione S-transferase (GSTU43) gene, which is involved in ALA-induced tolerance to oxidation stress and regulation of chlorophyll synthesis under low temperature.

RESULTS

Exogenous ALA alleviated low temperature caused chlorophyll synthesis obstacle of uroporphyrinogen III (UROIII) conversion to protoporphyrin IX (Proto IX), and enhanced the production of chlorophyll and its precursors, including endogenous ALA, Proto IX, Mg-protoporphyrin IX (Mg-proto IX), and protochlorophyll (Pchl), under low temperature in tomato leaves. However, ALA did not regulate chlorophyll synthesis at the level of transcription. Notably, ALA up-regulated the GSTU43 gene and protein expression and increased GST activity. Silencing of GSTU43 with virus-induced gene silencing reduced the activities of GST, superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, and increased the membrane lipid peroxidation; while fed with ALA significant increased all these antioxidase activities and antioxidant contents, and alleviated the membrane damage.

CONCLUSIONS

ALA triggered GST activity encoded by GSTU43, and increased tomato tolerance to low temperature-induced oxidative stress, perhaps with the assistance of ascorbate- and/or a glutathione-regenerating cycles, and actively regulated the plant redox homeostasis. This latter effect reduced the degree of membrane lipid peroxidation, which was essential for the coordinated synthesis of chlorophyll.

Plant Glutathione Transferases and Light

The activity and expression of glutathione transferases (GSTs) depend on several less-known endogenous and well-described exogenous factors, such as the developmental stage, presence, and intensity of different stressors, as well as on the absence or presence and quality of light, which to date have received less attention. In this review, we focus on discussing the role of circadian rhythm, light quality, and intensity in the regulation of plant GSTs. Recent studies demonstrate that diurnal regulation can be recognized in GST activity and gene expression in several plant species. In addition, the content of one of their co-substrates, reduced glutathione (GSH), also shows diurnal changes. Darkness, low light or shade mostly reduces GST activity, while high or excess light significantly elevates both the activity and expression of GSTs and GSH levels. Besides the light-regulated induction and dark inactivation of GSTs, these enzymes can also participate in the signal transduction of visible and UV light. For example, red light may alleviate the harmful effects of pathogens and abiotic stressors by increasing GST activity and expression, as well as GSH content in leaves of different plant species. Based on this knowledge, further research on plants (crops and weeds) or organs and temporal regulation of GST activity and gene expression is necessary for understanding the complex regulation of plant GSTs under various light conditions in order to increase the yield and stress tolerance of plants in the changing environment.

Functional, Structural and Biochemical Features of Plant Serinyl-Glutathione Transferases

Glutathione transferases (GSTs) belong to a ubiquitous multigenic family of enzymes involved in diverse biological processes including xenobiotic detoxification and secondary metabolism. A canonical GST is formed by two domains, the N-terminal one adopting a thioredoxin (TRX) fold and the C-terminal one an all-helical structure. The most recent genomic and phylogenetic analysis based on this domain organization allowed the classification of the GST family into 14 classes in terrestrial plants. These GSTs are further distinguished based on the presence of the ancestral cysteine (Cys-GSTs) present in TRX family proteins or on its substitution by a serine (Ser-GSTs). Cys-GSTs catalyze the reduction of dehydroascorbate and deglutathionylation reactions whereas Ser-GSTs catalyze glutathione conjugation reactions and eventually have peroxidase activity, both activities being important for stress tolerance or herbicide detoxification. Through non-catalytic, so-called ligandin properties, numerous plant GSTs also participate in the binding and transport of small heterocyclic ligands such as flavonoids including anthocyanins, and polyphenols. So far, this function has likely been underestimated compared to the other documented roles of GSTs. In this review, we compiled data concerning the known enzymatic and structural properties as well as the biochemical and physiological functions associated to plant GSTs having a conserved serine in their active site.

Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds

: Jasmonic acid (JA) and its related derivatives are ubiquitously occurring compounds of land plants acting in numerous stress responses and development. Recent studies on evolution of JA and other oxylipins indicated conserved biosynthesis. JA formation is initiated by oxygenation of α-linolenic acid (α-LeA, 18:3) or 16:3 fatty acid of chloroplast membranes leading to 12-oxo-phytodienoic acid (OPDA) as intermediate compound, but in Marchantiapolymorpha and Physcomitrellapatens, OPDA and some of its derivatives are final products active in a conserved signaling pathway. JA formation and its metabolic conversion take place in chloroplasts, peroxisomes and cytosol, respectively. Metabolites of JA are formed in 12 different pathways leading to active, inactive and partially active compounds. The isoleucine conjugate of JA (JA-Ile) is the ligand of the receptor component COI1 in vascular plants, whereas in the bryophyte M. polymorpha COI1 perceives an OPDA derivative indicating its functionally conserved activity. JA-induced gene expressions in the numerous biotic and abiotic stress responses and development are initiated in a well-studied complex regulation by homeostasis of transcription factors functioning as repressors and activators.