Conserved Function of Fibrillin5 in the Plastoquinone-9 Biosynthetic Pathway in Arabidopsis and Rice

Integrative leaf anatomy structure, physiology, and metabolome analyses revealed the response to drought stress in sainfoin at the seedling stage

INTRODUCTION

Sainfoin (Onobrychis viciaefolia) is a vital legume forage, and drought is the primary element impeding sainfoin growth.

OBJECTIVE

The anatomical structure, physiological indexes, and metabolites of the leaves of sainfoin seedlings with a drought-resistant line of P1 (DRL) and a drought-sensitive material of 2049 (DSM) were analyzed under drought (-1.0 MPa) with polyethylene glycol-6000 (PEG-6000).

METHODS

The leaf anatomy was studied by the paraffin section method. The related physiological indexes were measured by the hydroxylamine oxidation method, titanium sulfate colorimetric method, thiobarbituric acid method, acidic ninhydrin colorimetric method, and Coomassie brilliant blue method. The metabolomics analysis was composed of liquid chromatography tandem high-resolution mass spectrometry (LC-MS/MS).

RESULTS

The results revealed that the thickness of the epidermis, palisade tissue, and sponge tissue of DRL were significantly greater than those of DSM. The leaves of DRL exhibited lower levels of superoxide anion (O2 •-) production rate, hydrogen peroxide (H2O2) content, and malondialdehyde (MDA) content compared with DSM, while proline (Pro) content and soluble protein (SP) content were significantly higher than those of DSM. A total of 391 differential metabolites were identified in two samples. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment showed that the primary differential metabolites were concentrated into the tyrosine metabolism; isoquinoline alkaloid biosynthesis; ubiquinone and other terpenoid quinone biosynthesis; neomycin, kanamycin, and gentamicin biosynthesis; and anthocyanin biosynthesis metabolic pathways.

CONCLUSION

Compared with DSM, DRL had more complete anatomical structure, lower active oxygen content, and higher antioxidant level. The results improved our insights into the drought-resistant mechanisms in sainfoin.

Genome-Wide Characterization and Sequence Polymorphism Analyses of Glycine max Fibrillin (FBN) Revealed Its Role in Response to Drought Condition

The fibrillin (FBN) gene family is widely distributed in all photosynthetic organisms. Members of this gene family are involved in plant growth and development and their response to various biotic and abiotic stress factors. In this study, 16 members of FBN were identified in Glycine max and characterized by using different bioinformatics tools. Phylogenetic analysis classified FBN genes into seven groups. The presence of stress-related cis-elements in the upstream region of GmFBN highlighted their role in tolerance against abiotic stresses. To further decipher the function, physiochemical properties, conserved motifs, chromosomal localization, subcellular localization, and cis-acting regulatory elements were also analyzed. Gene expression analysis based on FPKM values revealed that GmFBNs greatly enhanced soybean drought tolerance and controlled the expression of several genes involved in drought response, except for GmFBN-4, GmFBN-5, GmFBN-6, GmFBN-7 and GmFBN-9. For high throughput genotyping, an SNP-based CAPS marker was also developed for the GmFBN-15 gene. The CAPS marker differentiated soybean genotypes based on the presence of either the GmFBN-15-G or GmFBN-15-A alleles in the CDS region. Association analysis showed that G. max accessions containing the GmFBN-15-A allele at the respective locus showed higher thousand seed weight compared to accessions containing the GmFBN-15-G allele. This research has provided the basic information to further decipher the function of FBN in soybean.

Genome-wide identification of the fibrillin gene family in chickpea (Cicer arietinum L.) and its response to drought stress

Fibrillin family members play multiple roles in growth, development, and protection against abiotic stress. In this study, we identified 12 potential CaFBNs that are ranging from 25 kDa-42.92 kDa and are mostly basic. These proteins were hydrophilic in nature and generally resided in the chloroplast. The CaFBN genes were located on different chromosomes like 1, 4, 5, and 7. All FBNs shared conserved motifs and possessed a higher number of stress-responsive elements. For evolutionary analysis, a phylogenetic tree of CaFBNs with other plants' FBNs was constructed and clustered into 11 FBN subgroups. For expression analysis, 21 day old chickpea seedling was exposed to dehydration stress by withholding water. We also performed various physiological and biochemical analyses to check that plant changes at the physiological and cellular levels while undergoing stress conditions. The transcript expression of CaFBNs was higher in aerial parts, especially in stems and leaves. Dehydration-specific transcriptome and qPCR analysis showed that FBN-1, FBN-2, and FBN-6 were highly expressed. In addition, our study provides a comprehensive overview of the FBN protein family and their importance during the dehydration stress condition in Cicer arietinum.

Effect of cerium on the production of reactive oxygen species in the root of Arabidopsis thaliana: An in vitro study

In the current study, the effect of trivalent cerium (Ce³⁺ ) on the production of reactive oxygen species (ROS) was investigated in the root of Arabidopsis thaliana by an in vitro study. The roots of A. thaliana were exposed with 0, 1, and 5 μmol/L Ce³⁺ for 12 h in vitro. It was found that the level of H₂ O₂ , O₂ ^.- , and ·OH was enhanced by 5 μmol/L Ce³⁺ , but reduced by 1 μmol/L Ce³⁺ . The activities of peroxidase (POD), catalase (CAT), and superoxidase dismutase (SOD) were enhanced by 1 μmol/L Ce³⁺ , but reduced by 5 μmol/L Ce³⁺ . Moreover, we used a laser-scanning confocal microscopy to detect the changes of ROS in the root cells of A. thaliana by using a fluorochrome 2',7'-dichlorofluorescein diacetate (H₂ DCF-DA). It showed that the level of ROS was declined in the root cells treated by 1 μmol/L Ce³⁺ , but the oscillation of ROS was found in the root cells treated with 5 μmol/L Ce³⁺ . In addition, REEs affect the uptake of mineral elements, which may be related to the oxidative stress in the cells of roots. In all, the data of our study indicated that the appropriate concentration of Ce³⁺ exhibited an anti-oxidation property and improved the defense system in the root cells of A. thaliana.

Chloroplast-localized PITP7 is essential for plant growth and photosynthetic function in Arabidopsis

Recent studies of chloroplast-localized Sec14-like protein (CPSFL1, also known as phosphatidylinositol transfer protein 7, PITP7) showed that CPSFL1 is necessary for photoautotropic growth and chloroplast vesicle formation in Arabidopsis (Arabidopsis thaliana). Here, we investigated the functional roles of CPSFL1/PITP7 using two A. thaliana mutants carrying a putative null allele (pitp7-1) and a weak allele (pitp7-2), respectively. PITP7 transcripts were undetectable in pitp7-1 and less abundant in pitp7-2 than in the wild-type (WT). The severity of mutant phenotypes, such as plant developmental abnormalities, levels of plastoquinone-9 (PQ-9) and chlorophylls, photosynthetic protein complexes, and photosynthetic performance, were well related to PITP7 transcript levels. The pitp7-1 mutation was seedling lethal and was associated with significantly lower levels of PQ-9 and major photosynthetic proteins. pitp7-2 plants showed greater susceptibility to high-intensity light stress than the WT, attributable to defects in nonphotochemical quenching and photosynthetic electron transport. PITP7 is specifically bound to phosphatidylinositol phosphates (PIPs) in lipid-binding assays in vitro, and the point mutations R82, H125, E162, or K233 reduced the binding affinity of PITP7 to PIPs. Further, constitutive expression of PITP7^H125Q or PITP7^E162K in pitp7-1 homozygous plants restored autotrophic growth in soil but without fully complementing the mutant phenotypes. Consistent with a previous study, our results demonstrate that PITP7 is essential for plant development, particularly the accumulation of PQ-9 and photosynthetic complexes. We propose a possible role for PITP7 in membrane trafficking of hydrophobic ligands such as PQ-9 and carotenoids through chloroplast vesicle formation or direct binding involving PIPs.

The mysterious role of fibrillin in plastid metabolism: current advances in understanding

Fibrillins (FBNs) are a family of genes in cyanobacteria, algae, and plants. The proteins they encode possess a lipid-binding motif, exist in various types of plastids, and are associated with lipid bodies called plastoglobules, implicating them in lipid metabolism. FBNs present in the thylakoid and stroma are involved in the storage, transport, and synthesis of lipid molecules for photoprotective functions against high-light stress. In this review, the diversity of subplastid locations in the evolution of FBNs, regulation of FBNs expression by various stresses, and the role of FBNs in plastid lipid metabolism are comprehensively summarized and directions for future research are discussed.

Chloroplast Localized FIBRILLIN11 Is Involved in the Osmotic Stress Response during Arabidopsis Seed Germination

Simple Summary

The FIBRILLIN11 (FBN11) of Arabidopsis has a lipid-binding FBN domain and a kinase domain. FBN11 is present in chloroplasts and is involved in salt and osmotic stress responses during seed germination. In mannitol, the seed germination rate of the fbn11 mutants significantly reduced compared to that of the wild type. The ABA-dependent and -independent stress response regulating genes were differentially expressed in fbn11 mutants and wild-type when grown in mannitol supplemented medium. These results suggest that chloroplast localized FBN11 is involved in mediating osmotic stress tolerance through the signaling pathway that regulates the stress response in the nucleus.

Abstract

Plants live in ever-changing environments, facing adverse environmental conditions including pathogen infection, herbivore attack, drought, high temperature, low temperature, nutrient deficiency, toxic metal soil contamination, high salt, and osmotic imbalance that inhibit overall plant growth and development. Plants have evolved mechanisms to cope with these stresses. In this study, we found that the FIBRILLIN11 (FBN11) gene in Arabidopsis, which has a lipid-binding FBN domain and a kinase domain, is involved in the plant’s response to abiotic stressors, including salt and osmotic stresses. FBN11 protein localizes to the chloroplast. FBN11 gene expression significantly changed when plants were exposed to the abiotic stress response mediators such as abscisic acid (ABA), sodium chloride (NaCl), and mannitol. The seed germination rates of fbn11 homozygous mutants in different concentrations of mannitol and NaCl were significantly reduced compared to wild type. ABA-dependent and -independent stress response regulatory genes were differentially expressed in the fbn11 mutant compared with wild type when grown in mannitol medium. These results suggest a clear role for chloroplast-localized FBN11 in mediating osmotic stress tolerance via the stress response regulatory signaling pathway in the nucleus.

The Predicted Functional Compartmentation of Rice Terpenoid Metabolism by Trans-Prenyltransferase Structural Analysis, Expression and Localization

Most terpenoids are derived from the basic terpene skeletons of geranyl pyrophosphate (GPP, C10), farnesyl-PP (FPP, C15) and geranylgeranyl-PP (GGPP, C20). The trans-prenyltransferases (PTs) mediate the sequential head-to-tail condensation of an isopentenyl-PP (C5) with allylic substrates. The in silico structural comparative analyses of rice trans-PTs with 136 plant trans-PT genes allowed twelve rice PTs to be identified as GGPS_LSU (OsGGPS1), homomeric G(G)PS (OsGPS) and GGPS_SSU-II (OsGRP) in Group I; two solanesyl-PP synthase (OsSPS2 and 3) and two polyprenyl-PP synthases (OsSPS1 and 4) in Group II; and five FPSs (OsFPS1, 2, 3, 4 and 5) in Group III. Additionally, several residues in "three floors" for the chain length and several essential domains for enzymatic activities specifically varied in rice, potentiating evolutionarily rice-specific biochemical functions of twelve trans-PTs. Moreover, expression profiling and localization patterns revealed their functional compartmentation in rice. Taken together, we propose the predicted topology-based working model of rice PTs with corresponding terpene metabolites: GPP/GGPPs mainly in plastoglobuli, SPPs in stroma, PPPs in cytosol, mitochondria and chloroplast and FPPs in cytosol. Our findings could be suitably applied to metabolic engineering for producing functional terpene metabolites in rice systems.

The comparison of transcriptomic response of green microalga Chlorella sorokiniana exposure to environmentally relevant concentration of cadmium(II) and 4-n-nonylphenol

The transcriptomic response of green microalga Chlorella sorokiniana exposure to environmentally relevant concentration of cadmium(II) (Cd) and 4-n-nonylphenol (4-n-NP) was compared in the present study. Cd and 4-n-NP exposure showed a similar pattern of dys-regulated pathways. The photosystem was affected due to suppression of chlorophyll biosynthesis via down-regulation of Mg-protoporphyrin IX chelatase subunit ChlD (CHLD) and divinyl chlorophyllide a 8-vinyl-reductase (DVR) in Cd group and via down-regulation of DVR in 4-n-NP group. Furthermore, the reactive oxygen species (ROS) could be induced through down-regulation of solanesyl diphosphate synthase 1 (SPS1) and homogentisate phytyltransferase (HPT) in Cd group and via down-regulation of HPT in 4-n-NP group. Additionally, Cd and 4-n-NP would both cause the dys-regulation of carbohydrate metabolism and protein synthesis. On the other hand, there are some different responses or detoxification mechanism of C. sorokiniana to 4-n-NP stress compared to Cd exposure. The increased ROS would cause the DNA damage and protein destruction in Cd exposure group. Simultaneously, the RNA transcription was dys-regulated and a series of changes in gene expressions were observed. This included lipid metabolism, protein modification, and DNA repair, which involved in response of C. sorokiniana to Cd stress or detoxification of Cd. For 4-n-NP exposure, no effect on lipid metabolism and DNA repair was observed. The nucleotide metabolism including pyrimidine metabolism and purine metabolism was significantly up-regulated in the 4-n-NP exposure group, but not in the Cd exposure group. In addition, 4-n-NP would induce the ubiquitin-mediated proteolysis and proteasomal degradation to diminish the misfolded protein caused by ROS and down-regulation of heat shocking protein 40. In sum, the Cd and 4-n-NP could cause the same toxicological effects via the common pathways and possess similar detoxification mechanism. They also showed different responses in nucleotide metabolism, lipid metabolism, and DNA repair.

Phylogeny, structural diversity and genome-wide expression analysis of fibrillin family genes in rice

Fibrillins (FBNs) constitute a plastid-lipid-associated protein family that plays a role in chloroplast development, lipids metabolism and stress responses in plants. Until now, FBNs have been functionally characterized in stability of thylakoid and responses to the different stress stimuli. Consequently, phylogeny, domain composition and structural features of 121 FBNs family proteins from ten representative species have been identified. As results, phylogenetic analysis demonstrated that FBNs proteins were grouped into 24 clades and further subdivided into three groups, including terrestrial plant-specific, algae-specific, and intermediate group. These FBNs genes had different numbers of introns and exons but encoded the conserved N-terminal chloroplast transport peptide (CTP) domains and plastid lipid-associated protein (PAP) domains, which greatly contributed to the sub-functionalization and neo-functionalization. Meanwhile, the CTP domains of eleven OsFBN proteins except OsFBN8 could help them transport into chloroplasts. The PAP domains of OsFBN2 and OsFBN4 showed the in vitro specific binding activity to C12-C22 fatty acids that were affected by YxD motif. The qRT-PCR analysis showed that OsFBN genes were differentially induced by heat stress and cold stress in rice. Collectively, this study has provided the new insights into the evolution, structure, and functions of FBN gene family and will help to elucidate the molecular mechanisms of these proteins functioning in growth, development and adaptations in the global climate change.

Genome-wide identification and characterization of the fibrillin gene family in Triticum aestivum

Background

The fibrillin (FBN) gene family is highly conserved and widely distributed in the photosynthetic organs of plants. Members of this gene family are involved in the growth and development of plants and their response to biotic and abiotic stresses. Wheat (Triticum aestivum), an important food crop, has a complex genetic background and little progress has occurred in the understanding of its molecular mechanisms.

Methods

In this study, we identified 26 FBN genes in the whole genome of T. aestivum through bioinformatic tools and biotechnological means. These genes were divided into 11 subgroups and were distributed on 11 chromosomes of T. aestivum. Interestingly, most of the TaFBN genes were located on the chromosomes 2A, 2B and 2D. The gene structure of each subgroup of gene family members and the position and number of motifs were highly similar.

Results

The evolutionary analysis results indicated that the affinities of FBNs in monocots were closer together. The tissue-specific analysis revealed that TaFBN genes were expressed in different tissues and developmental stages. In addition, some TaFBNs were involved in one or more biotic and abiotic stress responses. These results provide a basis for further study of the biological function of FBNs.

Overexpressing OsFBN1 enhances plastoglobule formation, reduces grain-filling percent and jasmonate levels under heat stress in rice

In higher plants, Fibrillins (FBNs) constitute a conserved plastid-lipid-associated (PAPs) protein family and modulate the metabolite transport and lipid metabolism in plastids of dicot species. However, FBNs have not functionally characterized in monocot species. In this study, the function of rice fibrillin 1 (OsFBN1) was investigated. The subcellular localization assay showed that the N-terminal chloroplast transport peptide (CTP) could facilitate the import of OsFBN1 into chloroplast. OsFBN1 specifically bound C18- and C20- fatty acids in vitro. Overexpressing OsFBN1 increased the tiller number but decreased the panicle length, grain-filling percent and JA levels compared to the wild type and RNAi silencing lines under heat stress. In addition, the overexpressing lines had more plastoglobules (PGs) than the wild type and RNAi silencing lines under both normal and heat stress conditions. Moreover, overexpressing OsFBN1 affected the transcription levels of OsAOS2 in JA synthesis, OsTHF1, OsABC1K7 and OsPsaE in thylakoid stability and photosynthesis, OsABC1-4 and OsSPS2 in ubiquinone-metabolism, OsHDR, OsDXR, and OsFPPS in isoprenoid metabolism. Collectively, these findings suggest the essential role of rice OsFBN1 in PG formation and lipid metabolism in chloroplasts, which coordinately regulate the growth and grain filling of the overexpressing lines under heat stress.

Functional Analysis of Polyprenyl Diphosphate Synthase Genes Involved in Plastoquinone and Ubiquinone Biosynthesis in Salvia miltiorrhiza

Polyprenyl diphosphate synthase (PPS) plays important roles in the biosynthesis of functionally important plastoquinone (PQ) and ubiquinone (UQ). However, only few plant PPS genes have been functionally characterized. Through genome-wide analysis, two PPS genes, termed SmPPS1 and SmPPS2, were identified from Salvia miltiorrhiza, an economically significant Traditional Chinese Medicine material and an emerging model medicinal plant. SmPPS1 and SmPPS2 belonged to different phylogenetic subgroups of plant trans-long-chain prenyltransferases and exhibited differential tissue expression and light-induced expression patterns. Computational prediction and transient expression assays showed that SmPPS1 was localized in the chloroplasts, whereas SmPPS2 was mainly localized in the mitochondria. SmPPS2, but not SmPPS1, could functionally complement the coq1 mutation in yeast cells and catalyzed the production of UQ-9 and UQ-10. Consistently, both UQ-9 and UQ-10 were detected in S. miltiorrhiza plants. Overexpression of SmPPS2 caused significant UQ accumulation in S. miltiorrhiza transgenics, whereas down-regulation resulted in decreased UQ content. Differently, SmPPS1 overexpression significantly elevated PQ-9 content in S. miltiorrhiza. Transgenic lines showing a down-regulation of SmPPS1 expression exhibited decreased PQ-9 level, abnormal chloroplast and trichome development, and varied leaf bleaching phenotypes. These results suggest that SmPPS1 is involved in PQ-9 biosynthesis, whereas SmPPS2 is involved in UQ-9 and UQ-10 biosynthesis.

Genome-Wide Identification and Expression Analyses of the Fibrillin Family Genes Suggest Their Involvement in Photoprotection in Cucumber

Fibrillin (FBN) is a plastid lipid-associated protein found in photosynthetic organisms from cyanobacteria to plants. In this study, 10 CsaFBN genes were identified in genomic DNA sequences of cucumber (Chinese long and Gy14) through database searches using the conserved domain of FBN and the 14 FBN genes of Arabidopsis. Phylogenetic analysis of CsaFBN protein sequences showed that there was no counterpart of Arabidopsis and rice FBN5 in the cucumber genome. FBN5 is essential for growth in Arabidopsis and rice; its absence in cucumber may be because of incomplete genome sequences or that another FBN carries out its functions. Among the 10 CsaFBN genes, CsaFBN1 and CsaFBN9 were the most divergent in terms of nucleotide sequences. Most of the CsaFBN genes were expressed in the leaf, stem and fruit. CsaFBN4 showed the highest mRNA expression levels in various tissues, followed by CsaFBN6, CsaFBN1 and CsaFBN9. High-light stress combined with low temperature decreased photosynthetic efficiency and highly induced transcript levels of CsaFBN1, CsaFBN6 and CsaFBN11, which decreased after 24 h treatment. Transcript levels of the other seven genes were changed only slightly. This result suggests that CsaFBN1, CsaFBN6 and CsaFBN11 may be involved in photoprotection under high-light conditions at low temperature.

Biosynthesis and applications of prenylquinones

Prenylquinones are isoprenoid compounds with a characteristic quinone structure and isoprenyl tail that are ubiquitous in almost all living organisms. There are four major prenylquinone classes: ubiquinone (UQ), menaquinone (MK), plastoquinone (PQ), and rhodoquinone (RQ). The quinone structure and isoprenyl tail length differ among organisms. UQ, PQ, and RQ contain benzoquinone, while MK contains naphthoquinone. UQ, MK, and RQ are involved in oxidative phosphorylation, while PQ functions in photosynthetic electron transfer. Some organisms possess two types of prenylquinones; Escherichia coli has UQ₈ and MK₈, and Caenorhabditis elegans has UQ₉ and RQ₉. Crystal structures of most of the enzymes involved in MK synthesis have been solved. Studies on the biosynthesis and functions of quinones have advanced recently, including for phylloquinone (PhQ), which has a phytyl moiety instead of an isoprenyl tail. Herein, the synthesis and applications of prenylquinones are reviewed.

Vitamin E Biosynthesis and Its Regulation in Plants

Vitamin E is one of the 13 vitamins that are essential to animals that do not produce them. To date, six natural organic compounds belonging to the chemical family of tocochromanols-four tocopherols and two tocotrienols-have been demonstrated as exhibiting vitamin E activity in animals. Edible plant-derived products, notably seed oils, are the main sources of vitamin E in the human diet. Although this vitamin is readily available, independent nutritional surveys have shown that human populations do not consume enough vitamin E, and suffer from mild to severe deficiency. Tocochromanols are mostly produced by plants, algae, and some cyanobacteria. Tocochromanol metabolism has been mainly studied in higher plants that produce tocopherols, tocotrienols, plastochromanol-8, and tocomonoenols. In contrast to the tocochromanol biosynthetic pathways that are well characterized, our understanding of the physiological and molecular mechanisms regulating tocochromanol biosynthesis is in its infancy. Although it is known that tocochromanol biosynthesis is strongly conditioned by the availability in homogentisate and polyprenyl pyrophosphate, its polar and lipophilic biosynthetic precursors, respectively, the mechanisms regulating their biosyntheses are barely known. This review summarizes our current knowledge of tocochromanol biosynthesis in plants, and highlights future challenges regarding the understanding of its regulation.