Transgenic production of epoxy fatty acids by expression of a cytochrome P450 enzyme from Euphorbia lagascae seed

A toolkit for plant lipid engineering: Surveying the efficacies of lipogenic factors for accumulating specialty lipids

Plants produce energy-dense lipids from carbohydrates using energy acquired via photosynthesis, making plant oils an economically and sustainably attractive feedstock for conversion to biofuels and value-added bioproducts. A growing number of strategies have been developed and optimized in model plants, oilseed crops and high-biomass crops to enhance the accumulation of storage lipids (mostly triacylglycerols, TAGs) for bioenergy applications and to produce specialty lipids with increased uses and value for chemical feedstock and nutritional applications. Most successful metabolic engineering strategies involve heterologous expression of lipogenic factors that outperform those from other sources or exhibit specialized functionality. In this review, we summarize recent progress in engineering the accumulation of triacylglycerols containing - specialized fatty acids in various plant species and tissues. We also provide an inventory of specific lipogenic factors (including accession numbers) derived from a wide variety of organisms, along with their reported efficacy in supporting the accumulation of desired lipids. A review of previously obtained results serves as a foundation to guide future efforts to optimize combinations of factors to achieve further enhancements to the production and accumulation of desired lipids in a variety of plant tissues and species.

Critical metabolic pathways and genes cooperate for epoxy fatty acid-enriched oil production in developing seeds of Vernonia galamensis, an industrial oleaginous plant

Background

Vernonia galamensis native to Africa is an annual oleaginous plant of Asteraceae family. As a newly established industrial oil crop, this plant produces high level (> 70%) of vernolic acid (cis-12-epoxyoctadeca-cis-9-enoic acid), which is an unusual epoxy fatty acid (EFA) with multiple industrial applications. Here, transcriptome analysis and fatty acid profiling from developing V. galamensis seeds were integrated to uncover the critical metabolic pathways responsible for high EFA accumulation, aiming to identify the target genes that could be used in the biotechnological production of high-value oils.

Results

Based on oil accumulation dynamics of V. galamensis seeds, we harvested seed samples from three stages (17, 38, and 45 days after pollination, DAP) representing the initial, fast and final EFA accumulation phases, and one mixed sample from different tissues for RNA-sequencing, with three biological replicates for each sample. Using Illumina platform, we have generated a total of 265 million raw cDNA reads. After filtering process, de novo assembly of clean reads yielded 67,114 unigenes with an N50 length of 1316 nt. Functional annotation resulted in the identification of almost all genes involved in diverse lipid-metabolic pathways, including the novel fatty acid desaturase/epoxygenase, diacylglycerol acyltransferases, and phospholipid:diacylglycerol acyltransferases. Expression profiling revealed that various genes associated with acyl editing, fatty acid β-oxidation, triacylglycerol assembly and oil-body formation had greater expression levels at middle developmental stage (38 DAP), which were consistent with the fast accumulation of EFA in V. galamensis developing seed, these genes were detected to play fundamental roles in EFA production. In addition, we isolated some transcription factors (such as WRI1, FUS3 and ABI4), which putatively regulated the production of V. galamensis seed oils. The transient expression of the selected genes resulted in a synergistic increase of EFA-enriched TAG accumulation in tobacco leaves. Transcriptome data were further confirmed by quantitative real-time PCR for twelve key genes in EFA biosynthesis. Finally, a comprehensive network for high EFA accumulation in V. galamensis seed was established.

Conclusions

Our findings provide new insights into molecular mechanisms underlying the natural epoxy oil production in V. galamensis. A set of genes identified here could be used as the targets to develop other oilseeds highly accumulating valued epoxy oils for commercial production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02120-2.

A multigene approach secures hydroxy fatty acid production in Arabidopsis

A central goal of green chemistry is to produce industrially useful fatty acids in oilseed crops. Although genes encoding suitable fatty acid-modifying enzymes are available from more than a dozen wild species, progress has been limited because expression of these enzymes in transgenic plants produces only low yields of the desired products. For example, fatty acid hydroxylase 12 (FAH12) from castor (Ricinus communis) produces only 17% hydroxy fatty acids (HFAs) when expressed in Arabidopsis (Arabidopsis thaliana), compared with 90% HFAs in castor seeds. The transgenic plants also have reduced oil content and seed vigor. Here, we review experiments that have provided for steady increased HFA accumulation and oil content. This research has led to exciting new discoveries of enzymes and regulatory processes in the pathways of both seed oil synthesis and lipid metabolism in other parts of the plant. Recent investigations have revealed that HFA-accumulating seeds are unable to rapidly mobilize HFA-containing triacylglycerol (TAG) storage lipid after germination to provide carbon and energy for seedling development, resulting in reduced seedling establishment. These findings present a new opportunity to investigate a different, key area of lipid metabolism-the pathways of TAG lipolysis and β-oxidation in germinating seedlings.

Structural diversity, biosynthesis, and function of plant falcarin-type polyacetylenic lipids

The polyacetylenic lipids falcarinol, falcarindiol, and associated derivatives, termed falcarins, have a widespread taxonomical distribution in the plant kingdom and have received increasing interest for their demonstrated health-promoting properties as anti-cancer and anti-inflammatory agents. These fatty acid-derived compounds are also linked to plant pathogen resistance through their potent antimicrobial properties. Falcarin-type polyacetylenes, which contain two conjugated triple bonds, are derived from structural modifications of the common fatty acid oleic acid. In the past half century, much progress has been made in understanding the structural diversity of falcarins in the plant kingdom, whereas limited progress has been made on elucidating falcarin function in plant-pathogen interactions. More recently, an understanding of the biosynthetic machinery underlying falcarin biosynthesis has emerged. This review provides a concise summary of the current state of knowledge on falcarin structural diversity, biosynthesis, and plant defense properties. We also present major unanswered questions about falcarin biosynthesis and function.

CYP77B1 a fatty acid epoxygenase specific to flowering plants

Contrary to animals, little is known in plants about enzymes able to produce fatty acid epoxides. In our attempt to find and characterize a new fatty acid epoxygenase in Arabidopsis thaliana, data mining brought our attention on CYP77B1. Modification of the N-terminus was necessary to get enzymatic activity after heterologous expression in yeast. The common plant fatty acid C18:2 was converted into the diol 12,13-dihydroxy-octadec-cis-9-enoic acid when incubated with microsomes of yeast expressing modified CYP77B1 and AtEH1, a soluble epoxide hydrolase. This diol originated from the hydrolysis by AtEH1 of the epoxide 12,13-epoxy-octadec-cis-9-enoic acid produced by CYP77B1. A spatio-temporal study of CYP77B1 expression performed with RT-qPCR revealed the highest level of transcripts in flower bud while, in open flower, the enzyme was mainly present in pistil. CYP77B1 promoter-driven GUS expression confirmed reporter activities in pistil and also in stamens and petals. In silico co-regulation data led us to hypothesize that CYP77B1 could be involved in cutin synthesis but when flower cutin of loss-of-function mutants cyp77b1 was analyzed, no difference was found compared to cutin of wild type plants. Phylogenetic analysis showed that CYP77B1 is strictly conserved in flowering plants, suggesting a specific function in this lineage.

Oxidative Stability of Vegetal Oil-Based Lubricants

Lipids are widely distributed in nature and are one of the most important components of natural foods, synthetic compounds, and emulsions. To date, there is a strong social demand in the industrial sector for the use of sustainable products with a minimal environmental impact. Depending on their origin and composition, lipids can be employed as a plausible alternative as biodegradable lubricants in order to reduce the use of conventional mineral oil lubricants and mitigate their environmental impact. This perspective provides an overview of the advantages and constrains of vegetal oils under different lubrication regimes and the tribochemical reactions that can take place. Also, the different factors and pathways that influence their oxidation, the key role of moisture, and the changes of physical properties under pressure and temperature are reviewed. Special emphasis is devoted to the oxidation instability of fatty acids and vegetal oils and the physical and chemical approaches to improve oxidative and thermal stability are described in detail.

Pathway elucidation and engineering of plant-derived diterpenoids

Plant-derived diterpenoids are indispensable to plant development, stress-resistance and interaction with environmental microorganisms. Besides significant roles in plant fitness and adaption, many bioactivities beneficial to human beings are also found in diterpenoids from terrestrial plants. However, these high-value compounds are always present in limited species with low-abundance. Complicated chemosynthesis hardly meets the needs of sufficient supplies. To overcome these obstacles, it is necessary to investigate how diterpenoids are biosynthesized in planta, and followed by engineering the biosynthetic pathway to achieve high yield production. This review will summarize the recent progress of plant diterpenoid biosynthetic pathway discovery and engineering, hoping to offer an inspiration for concerned researchers.

Alteration of the fatty acid composition of Brassica napus L. via overexpression of phospholipid: Diacylglycerol acyltransferase 1 from Sapium sebiferum (L.) Roxb

Sapium sebiferum (L.) Roxb. plays an important role in traditional Chinese medicine and is one of major woody oil tree in China. Phospholipid: diacylglycerol acyltransferase 1 (PDAT1), as an important catalytic enzyme for the formation of triacylglycerol (TAG), is mainly responsible for the transfer of an acyl group from the sn-2 position of phospholipids to the sn-3 position of sn-1, 2-diacylglycerol (DAG) to produce TAG and sn-1 lysophospholipids. The importance of PDAT1 in triacylglycerol biosynthesis has been illustrated in previous research, and at least 67 PDAT1 sequences have been identified from 31 organisms. However, little is known about the gene encoding PDAT1 in S. sebiferum (SsPDAT1), which is involved in seed oil biosynthesis. To explore the functional characteristics of SsPDAT1, we cloned and analyzed the full-length cDNA in the coding region of SsPDAT1, which consists of 2040 bp and encodes a putative protein of 680 amino acid (aa) residues. Thin-layer chromatography (TLC) analysis showed that recombinant SsPDAT1 could restore TAG accumulation in TAG-deficient mutant yeast (Saccharomyces cerevisiae) H1246, which revealed the enzyme activity of SsPDAT1. Moreover, transgenic Brassica napus L. W10 plants overexpressing SsPDAT1 showed significant increases of 19.6-28.9 % in linoleic acid levels but decreases of 27.3-37.1 % in linolenic acid. Furthermore, the total oil content increased by 8.1 %-10.8 % in SsPDAT1 transgenic seeds. These results confirmed the role of SsPDAT1 in stabilizing oil biosynthesis and suggested that SsPDAT1 could be exploitable to specifically regulate the oil composition of plants. These experimental results provide a new concept that may enable the industrial development of plants with high-linoleic-acid oil through overexpression of SsPDAT1 in S. sebiferum L.

Metabolic Engineering a Model Oilseed Camelina sativa for the Sustainable Production of High-Value Designed Oils

Camelina sativa (L.) Crantz is an important Brassicaceae oil crop with a number of excellent agronomic traits including low water and fertilizer input, strong adaptation and resistance. Furthermore, its short life cycle and easy genetic transformation, combined with available data of genome and other "-omics" have enabled camelina as a model oil plant to study lipid metabolism regulation and genetic improvement. Particularly, camelina is capable of rapid metabolic engineering to synthesize and accumulate high levels of unusual fatty acids and modified oils in seeds, which are more stable and environmentally friendly. Such engineered camelina oils have been increasingly used as the super resource for edible oil, health-promoting food and medicine, biofuel oil and high-valued chemical production. In this review, we mainly highlight the latest advance in metabolic engineering towards the predictive manipulation of metabolism for commercial production of desirable bio-based products using camelina as an ideal platform. Moreover, we deeply analysis camelina seed metabolic engineering strategy and its promising achievements by describing the metabolic assembly of biosynthesis pathways for acetyl glycerides, hydroxylated fatty acids, medium-chain fatty acids, ω-3 long-chain polyunsaturated fatty acids, palmitoleic acid (ω-7) and other high-value oils. Future prospects are discussed, with a focus on the cutting-edge techniques in camelina such as genome editing application, fine directed manipulation of metabolism and future outlook for camelina industry development.

GhFAD2-3 is required for anther development in Gossypium hirsutum

BACKGROUND

In higher plants, the FAD2 gene encodes the microsomal oleate ^Δ12-desaturase, one of the key enzymes essential for the biosynthesis of the polyunsaturated lipids that serve many important functions in plant development and stress responses. FAD2 catalyzes the first step, in the biosynthesis of the polyunsaturated fatty acids (PUFAs) found in the cell membrane and cell wall, and it is thus of great importance to investigate the regulatory role of FAD2 in anther development.

RESULTS

We reported the molecular characterization of the cotton (Gossypium hirsutum) GhFAD2 gene family and the essential role of GhFAD2-3 in cotton anther development. G. hirsutum contains four pairs of homoeologous FAD2 genes (GhFAD2-1 to GhFAD2-4). GhFAD2-3 is ubiquitously and relatively highly expressed in all analyzed tissues, particularly in anthers. Specific inhibition of GhFAD2-3 using the RNA interference approach resulted in male sterility due to impaired anther development at the stages from meiosis to maturation. The cellular phenotypic abnormality observed at the meiosis stage of the GhFAD2-3 silenced plant (fad2-3) coincides with the significant reduction of C18:2 in anthers at the same stage. Compared with that of the wild type (WT), the content of C18:1 was 41.48%, which increased by 5 fold in the fad2-3 anther at the pollen maturation stage. Moreover, the ratio of monounsaturated to polyunsaturated fatty acid was 5.43 in fad2-3 anther, which was much higher than that of the WT (only 0.39). Through compositional analysis of anthers cuticle and transcriptome data, we demonstrated it was unfavorable to the development of anther by regulating GhFAD2-3 expression level to increase the oleic acid content.

CONCLUSIONS

Our work demonstrated the importance of C18:2 and/or C18:3 in the development of the pollen exine and anther cuticle in cotton and provided clue for further investigation of the physiological significance of the fatty acid composition for plant growth and development.

GhFAD2-3 is required for anther development in Gossypium hirsutum

BACKGROUND

In higher plants, the FAD2 gene encodes the microsomal oleate ^Δ12-desaturase, one of the key enzymes essential for the biosynthesis of the polyunsaturated lipids that serve many important functions in plant development and stress responses. FAD2 catalyzes the first step, in the biosynthesis of the polyunsaturated fatty acids (PUFAs) found in the cell membrane and cell wall, and it is thus of great importance to investigate the regulatory role of FAD2 in anther development.

RESULTS

We reported the molecular characterization of the cotton (Gossypium hirsutum) GhFAD2 gene family and the essential role of GhFAD2-3 in cotton anther development. G. hirsutum contains four pairs of homoeologous FAD2 genes (GhFAD2-1 to GhFAD2-4). GhFAD2-3 is ubiquitously and relatively highly expressed in all analyzed tissues, particularly in anthers. Specific inhibition of GhFAD2-3 using the RNA interference approach resulted in male sterility due to impaired anther development at the stages from meiosis to maturation. The cellular phenotypic abnormality observed at the meiosis stage of the GhFAD2-3 silenced plant (fad2-3) coincides with the significant reduction of C18:2 in anthers at the same stage. Compared with that of the wild type (WT), the content of C18:1 was 41.48%, which increased by 5 fold in the fad2-3 anther at the pollen maturation stage. Moreover, the ratio of monounsaturated to polyunsaturated fatty acid was 5.43 in fad2-3 anther, which was much higher than that of the WT (only 0.39). Through compositional analysis of anthers cuticle and transcriptome data, we demonstrated it was unfavorable to the development of anther by regulating GhFAD2-3 expression level to increase the oleic acid content.

CONCLUSIONS

Our work demonstrated the importance of C18:2 and/or C18:3 in the development of the pollen exine and anther cuticle in cotton and provided clue for further investigation of the physiological significance of the fatty acid composition for plant growth and development.

Metabolic engineering for enhanced oil in biomass

The world is hungry for energy. Plant oils in the form of triacylglycerol (TAG) are one of the most reduced storage forms of carbon found in nature and hence represent an excellent source of energy. The myriad of applications for plant oils range across foods, feeds, biofuels, and chemical feedstocks as a unique substitute for petroleum derivatives. Traditionally, plant oils are sourced either from oilseeds or tissues surrounding the seed (mesocarp). Most vegetative tissues, such as leaves and stems, however, accumulate relatively low levels of TAG. Since non-seed tissues constitute the majority of the plant biomass, metabolic engineering to improve their low-intrinsic TAG-biosynthetic capacity has recently attracted significant attention as a novel, sustainable and potentially high-yielding oil production platform. While initial attempts predominantly targeted single genes, recent combinatorial metabolic engineering strategies have focused on the simultaneous optimization of oil synthesis, packaging and degradation pathways (i.e., 'push, pull, package and protect'). This holistic approach has resulted in dramatic, seed-like TAG levels in vegetative tissues. With the first proof of concept hurdle addressed, new challenges and opportunities emerge, including engineering fatty acid profile, translation into agronomic crops, extraction, and downstream processing to deliver accessible and sustainable bioenergy.

PlantFAdb: a resource for exploring hundreds of plant fatty acid structures synthesized by thousands of plants and their phylogenetic relationships

Over 450 structurally distinct fatty acids are synthesized by plants. We have developed PlantFAdb.org, an internet-based database that allows users to search and display fatty acid composition data for over 9000 plants. PlantFAdb includes more than 17 000 data tables from >3000 publications and hundreds of unpublished analyses. This unique feature allows users to easily explore chemotaxonomic relationships between fatty acid structures and plant species by displaying these relationships on dynamic phylogenetic trees. Users can navigate between order, family, genus and species by clicking on nodes in the tree. The weight percentage of a selected fatty acid is indicated on phylogenetic trees and clicking in the graph leads to underlying data tables and publications. The display of chemotaxonomy allows users to quickly explore the diversity of plant species that produce each fatty acid and that can provide insights into the evolution of biosynthetic pathways. Fatty acid compositions and other parameters from each plant species have also been compiled from multiple publications on a single page in graphical form. Links provide simple and intuitive navigation between fatty acid structures, plant species, data tables and the publications that underlie the datasets. In addition to providing an introduction to this resource, this report illustrates examples of insights that can be derived from PlantFAdb. Based on the number of plant families and orders that have not yet been surveyed we estimate that a large number of novel fatty acid structures are still to be discovered in plants.

Seeds as oil factories

Studying seed oil metabolism. The seeds of higher plants represent valuable factories capable of converting photosynthetically derived sugars into a variety of storage compounds, including oils. Oils are the most energy-dense plant reserves and fatty acids composing these oils represent an excellent nutritional source. They supply humans with much of the calories and essential fatty acids required in their diet. These oils are then increasingly being utilized as renewable alternatives to petroleum for the chemical industry and for biofuels. Plant oils therefore represent a highly valuable agricultural commodity, the demand for which is increasing rapidly. Knowledge regarding seed oil production is extensively exploited in the frame of breeding programs and approaches of metabolic engineering for oilseed crop improvement. Complementary aspects of this research include (1) the study of carbon metabolism responsible for the conversion of photosynthetically derived sugars into precursors for fatty acid biosynthesis, (2) the identification and characterization of the enzymatic actors allowing the production of the wide set of fatty acid structures found in seed oils, and (3) the investigation of the complex biosynthetic pathways leading to the production of storage lipids (waxes, triacylglycerols). In this review, we outline the most recent developments in our understanding of the underlying biochemical and molecular mechanisms of seed oil production, focusing on fatty acids and oils that can have a significant impact on the emerging bioeconomy.

P450s controlling metabolic bifurcations in plant terpene specialized metabolism

ABSTRACT

Catalyzing stereo- and regio-specific oxidation of inert hydrocarbon backbones, and a range of more exotic reactions inherently difficult in formal chemical synthesis, cytochromes P450 (P450s) offer outstanding potential for biotechnological engineering. Plants and their dazzling diversity of specialized metabolites have emerged as rich repository for functional P450s with the advances of deep transcriptomics and genome wide discovery. P450s are of outstanding interest for understanding chemical diversification throughout evolution, for gaining mechanistic insights through the study of their structure-function relationship, and for exploitation in Synthetic Biology. In this review, we highlight recent developments and examples in the discovery of plant P450s involved in the biosynthesis of industrially relevant monoterpenoids, sesquiterpenoids, diterpenoids and triterpenoids, throughout 2016 and early 2017. Examples were selected to illustrate the spectrum of value from commodity chemicals, flavor and fragrance compounds to pharmacologically active terpenoids. We focus on a recently emerging theme, where P450s control metabolic bifurcations and chemical diversity of the final product profile, either within a pathway, or through neo-functionalization in related species. The implications may inform approaches for rational assembly of recombinant pathways, biotechnological production of high value terpenoids and generation of novel chemical entities.

In vitro synthesis of 9,10-dihydroxyhexadecanoic acid using recombinant Escherichia coli

Background

Hydroxy fatty acids are widely used in food, chemical and cosmetic industries. A variety of dihydroxy fatty acids have been synthesized so far; however, no studies have been done on the synthesis of 9,10-dihydroxyhexadecanoic acid. In the present study recombinant E. coli has been used for the heterologous expression of fatty acid hydroxylating enzymes and the whole cell lysate of the induced culture was used for in vitro production of 9,10-dihydroxyhexadecanoic acid.

Results

A first of its kind proof of principle has been successfully demonstrated for the production of 9,10-dihydroxyhexadecanoic acid using three different enzymes viz. fatty acid desaturase (FAD) from Saccharomyces cerevisiae, epoxide hydrolase (EH) from Caenorhabditis elegance and epoxygenase (EPOX) from Stokasia laevis. The genes for these proteins were codon-optimised, synthesised and cloned in pET 28a (+) vector. The culture conditions for induction of these three proteins in E. coli were optimised in shake flask. The induced cell lysates were used both singly and in combination along with the trans-supply of hexadecanoic acid and 9-hexadecenoic acid, followed by product profiling by GC–MS. Formation of 9,10-dihydroxyhexadecanoic acid was successfully achieved when combination of induced cell lysates of recombinant E. coli containing FAD, EH, and EPOX were incubated with 9-hexadecenoic acid.

Conclusions

The in vitro production of 9,10-dihydroxyhexadecanoic acid synthesis using three fatty acid modification genes from different sources has been successfully demonstrated. The strategy adopted can be used for the production of similar compounds.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0696-7) contains supplementary material, which is available to authorized users.

Phospholipase Dζ Enhances Diacylglycerol Flux into Triacylglycerol

Plant seeds are the primary source of triacylglycerols (TAG) for food, feed, fuel, and industrial applications. As TAG is produced from diacylglycerol (DAG), successful engineering strategies to enhance TAG levels have focused on the conversion of DAG to TAG. However, the production of TAG can be limited by flux through the enzymatic reactions that supply DAG. In this study, two Arabidopsis phospholipase D_ζ genes (AtPLD_ζ1 and AtPLD_ζ2 ) were coexpressed in Camelina sativa to test whether the conversion of phosphatidylcholine to DAG impacts TAG levels in seeds. The resulting transgenic plants produced 2% to 3% more TAG as a component of total seed biomass and had increased 18:3 and 20:1 fatty acid levels relative to wild type. Increased DAG and decreased PC levels were examined through the kinetics of lipid assembly by [¹⁴C]acetate and [¹⁴C]glycerol incorporation into glycerolipids. [¹⁴C]acetate was rapidly incorporated into TAG in both wild-type and overexpression lines, indicating a significant flux of nascent and elongated acyl-CoAs into the sn-3 position of TAG. Stereochemical analysis revealed that newly synthesized fatty acids were preferentially incorporated into the sn-2 position of PC, but the sn-1 position of de novo DAG and indicated similar rates of nascent acyl groups into the Kennedy pathway and acyl editing. [¹⁴C]glycerol studies demonstrated PC-derived DAG is the major source of DAG for TAG synthesis in both tissues. The results emphasize that the interconversions of DAG and PC pools can impact oil production and composition.

Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L

The seed oil of Euphorbia lathyris L. contains a series of macrocyclic diterpenoids known as Euphorbia factors. They are the current industrial source of ingenol mebutate, which is approved for the treatment of actinic keratosis, a precancerous skin condition. Here, we report an alcohol dehydrogenase-mediated cyclization step in the biosynthetic pathway of Euphorbia factors, illustrating the origin of the intramolecular carbon-carbon bonds present in lathyrane and ingenane diterpenoids. This unconventional cyclization describes the ring closure of the macrocyclic diterpene casbene. Through transcriptomic analysis of E. lathyris L. mature seeds and in planta functional characterization, we identified three enzymes involved in the cyclization route from casbene to jolkinol C, a lathyrane diterpene. These enzymes include two cytochromes P450 from the CYP71 clan and an alcohol dehydrogenase (ADH). CYP71D445 and CYP726A27 catalyze regio-specific 9-oxidation and 5-oxidation of casbene, respectively. When coupled with these P450-catalyzed monooxygenations, E. lathyris ADH1 catalyzes dehydrogenation of the hydroxyl groups, leading to the subsequent rearrangement and cyclization. The discovery of this nonconventional cyclization may provide the key link to complete elucidation of the biosynthetic pathways of ingenol mebutate and other bioactive macrocyclic diterpenoids.

Research progress relating to the role of cytochrome P450 in the biosynthesis of terpenoids in medicinal plants

Terpenoids are an extensive and diverse group of plant secondary metabolites. To date, they have been applied in many fields including industry, medicine and health. The wide variety of terpenoid compounds cannot arise solely from simple cyclisations of a precursor molecule or from a single-step reaction; their structural diversity depends on the modification of many specific chemical groups, rearrangements of their skeletal structures and on the post-modification reactions. Most of the post-modification enzymes that catalyse these reactions are cytochrome P450 monooxygenases. Therefore, the discovery and identification of plant P450 genes plays a vital role in the exploration of terpenoid biosynthesis pathways. This review summarises recent research progress relating to the function of plant cytochrome P450 enzymes, describes P450 genes that have been cloned from full-length cDNA and identifies the function of P450 enzymes in the terpenoid biosynthesis pathways of several medicinal plants.

Over-expression of JcDGAT1 from Jatropha curcas increases seed oil levels and alters oil quality in transgenic Arabidopsis thaliana

The increasing consumption of fossil fuels and petroleum products is leading to their rapid depletion and is a matter of concern around the globe. Substitutes of fossil fuels are required to sustain the pace of economic development. In this context, oil from the non food crops (biofuel) has shown potential to substitute fossil fuels. Jatropha curcas is an excellent shrub spread and naturalized across the globe. Its oil contains a high percentage of unsaturated fatty acids (about 78-84% of total fatty acid content) making the oil suitable for biodiesel production. Despite its high oil content, it has been poorly studied in terms of important enzymes/genes responsible for oil biosynthesis. Here, we describe the isolation of the full length cDNA clone of JcDGAT1, a key enzyme involved in oil biosynthesis, from J. curcas seeds and manipulation of oil content and composition in transgenic Arabidopsis plants by its expression. Transcript analysis of JcDGAT1 reveals a gradual increase from early seed development to its maturation. Homozygous transgenic Arabidopsis lines expressing JcDGAT1 both under CaMV35S promoter and a seed specific promoter show an enhanced level of total oil content (up by 30-41%) in seeds but do not show any phenotypic differences. In addition, our studies also show alterations in the oil composition through JcDGAT1 expression. While the levels of saturated FAs such as palmitate and stearate in the oil do not change, there is significant reproducible decrease in the levels of oleic acid and a concomitant increase in levels of linolenic acid both under the CaMV35S promoter as well as the seed specific promoter. Our studies thus confirm that DGAT is involved in flux control in oil biosynthesis and show that JcDGAT1 could be used specifically to manipulate and improve oil content and composition in plants.

Characterisation of the FAD2 gene family from Hiptage benghalensis: a ricinoleic acid accumulating plant

We have characterised the FAD2 gene family from Hiptage benghalensis, a tropical plant that accumulates high levels of ricinoleic acid in its seeds. Functional characterisation of six FAD2 gene family members showed that two of them were capable of functioning as Δ12-hydroxylases while the other FAD2 members were confirmed to be Δ12-desaturases. The Δ12-hydroxylation function of these two genes was confirmed in yeast cells, using C16:1(Δ9) and C18:1(Δ9) monounsaturated fatty acids as substrates. These Δ12-hydroxylases, like the other Δ12-hydroxylases previously cloned from plants Ricinus communis (castor), Physaria fendleri and fungus Claviceps purpurea, also showed some Δ12-desaturase activity. The hydroxylation activity of the two Hiptage hydroxylases was further confirmed by their expression in the Arabidopsis fad2/fae1 double mutant where they were able to produce equivalent or higher levels hydroxylated fatty acids in the seed oil when compared with the other known hydroxylases.

An integrative "omics" approach identifies new candidate genes to impact aroma volatiles in peach fruit

BACKGROUND

Ever since the recent completion of the peach genome, the focus of genetic research in this area has turned to the identification of genes related to important traits, such as fruit aroma volatiles. Of the over 100 volatile compounds described in peach, lactones most likely have the strongest effect on fruit aroma, while esters, terpenoids, and aldehydes have minor, yet significant effects. The identification of key genes underlying the production of aroma compounds is of interest for any fruit-quality improvement strategy.

RESULTS

Volatile (52 compounds) and gene expression (4348 genes) levels were profiled in peach fruit from a maturity time-course series belonging to two peach genotypes that showed considerable differences in maturation characteristics and postharvest ripening. This data set was analyzed by complementary correlation-based approaches to discover the genes related to the main aroma-contributing compounds: lactones, esters, and phenolic volatiles, among others. As a case study, one of the candidate genes was cloned and expressed in yeast to show specificity as an ω-6 Oleate desaturase, which may be involved in the production of a precursor of lactones/esters.

CONCLUSIONS

Our approach revealed a set of genes (an alcohol acyl transferase, fatty acid desaturases, transcription factors, protein kinases, cytochromes, etc.) that are highly associated with peach fruit volatiles, and which could prove useful in breeding or for biotechnological purposes.

Assessment of oil content and fatty acid composition variability in two economically important Hibiscus species

The Hibiscus genus encompasses more than 300 species, but kenaf (Hibiscus cannabinus L.) and roselle (Hibiscus sabdariffa L.) are the two most economically important species within the genus. Seeds from these two Hibiscus species contain a relatively high amount of oil with two unusual fatty acids: dihydrosterculic and vernolic acids. The fatty acid composition in the oil can directly affect oil quality and its utilization. However, the variability in oil content and fatty acid composition for these two species is unclear. For these two species, 329 available accessions were acquired from the USDA germplasm collection. Their oil content and fatty acid composition were determined by nuclear magnetic resonance (NMR) and gas chromatography (GC), respectively. Using NMR and GC analyses, we found that Hibiscus seeds on average contained 18% oil and seed oil was composed of six major fatty acids (each >1%) and seven minor fatty acids (each <1%). Hibiscus cannabinus seeds contained significantly higher amounts of oil (18.14%), palmitic (20.75%), oleic (28.91%), vernolic acids (VA, 4.16%), and significantly lower amounts of stearic (3.96%), linoleic (39.49%), and dihydrosterculic acids (DHSA, 1.08%) than H. sabdariffa seeds (17.35%, 18.52%, 25.16%, 3.52%, 4.31%, 44.72%, and 1.57%, respectively). For edible oils, a higher oleic/linoleic (O/L) ratio and lower level of DHSA are preferred, and for industrial oils a high level of VA is preferred. Our results indicate that seeds from H. cannabinus may be of higher quality than H. sabdariffa seeds for these reasons. Significant variability in oil content and major fatty acids was also detected within both species. The variability in oil content and fatty acid composition revealed from this study will be useful for exploring seed utilization and developing new cultivars in these Hibiscus species.

Vernonia DGATs can complement the disrupted oil and protein metabolism in epoxygenase-expressing soybean seeds

Plant oils can be useful chemical feedstocks such as a source of epoxy fatty acids. High seed-specific expression of a Stokesia laevis epoxygenase (SlEPX) in soybeans only results in 3-7% epoxide levels. SlEPX-transgenic soybean seeds also exhibited other phenotypic alterations, such as altered seed fatty acid profiles, reduced oil accumulation, and variable protein levels. SlEPX-transgenic seeds showed a 2-5% reduction in total oil content and protein levels of 30.9-51.4%. To address these pleiotrophic effects of SlEPX expression on other traits, transgenic soybeans were developed to co-express SlEPX and DGAT (diacylglycerol acyltransferase) genes (VgDGAT1 & 2) isolated from Vernonia galamensis, a high accumulator of epoxy fatty acids. These side effects of SlEPX expression were largely overcome in the DGAT co-expressing soybeans. Total oil and protein contents were restored to the levels in non-transgenic soybeans, indicating that both VgDGAT1 and VgDGAT2 could complement the disrupted phenotypes caused by over-expression of an epoxygenase in soybean seeds.

Recent advances in soybean transformation and their application to molecular breeding and genomic analysis

Herbicide-resistant transgenic soybean plants hold a leading market share in the USA and other countries, but soybean has been regarded as recalcitrant to transformation for many years. The cumulative and, at times, exponential advances in genetic manipulation have made possible further choices for soybean transformation. The most widely and routinely used transformation systems are cotyledonary node-Agrobacterium-mediated transformation and somatic embryo-particle-bombardment-mediated transformation. These ready systems enable us to improve seed qualities and agronomic characteristics by transgenic approaches. In addition, with the accumulation of soybean genomic resources, convenient or promising approaches will be requisite for the determination and use of gene function in soybean. In this article, we describe recent advances in and problems of soybean transformation, and survey the current transgenic approaches for applied and basic research in Japan.

A peroxygenase pathway involved in the biosynthesis of epoxy fatty acids in oat

While oat (Avena sativa) has long been known to produce epoxy fatty acids in seeds, synthesized by a peroxygenase pathway, the gene encoding the peroxygenase remains to be determined. Here we report identification of a peroxygenase cDNA AsPXG1 from developing seeds of oat. AsPXG1 is a small protein with 249 amino acids in length and contains conserved heme-binding residues and a calcium-binding motif. When expressed in Pichia pastoris and Escherichia coli, AsPXG1 catalyzes the strictly hydroperoxide-dependent epoxidation of unsaturated fatty acids. It prefers hydroperoxy-trienoic acids over hydroperoxy-dienoic acids as oxygen donors to oxidize a wide range of unsaturated fatty acids with cis double bonds. Oleic acid is the most preferred substrate. The acyl carrier substrate specificity assay showed phospholipid and acyl-CoA were not effective substrate forms for AsPXG1 and it could only use free fatty acid or fatty acid methyl esters as substrates. A second gene, AsLOX2, cloned from oat codes for a 9-lipoxygenase catalyzing the synthesis of 9-hydroperoxy-dienoic and 9-hydroperoxy-trienoic acids, respectively, when linoleic (18:2-9c,12c) and linolenic (18:3-9c,12c,15c) acids were used as substrates. The peroxygenase pathway was reconstituted in vitro using a mixture of AsPXG1 and AsLOX2 extracts from E. coli. Incubation of methyl oleate and linoleic acid or linolenic acid with the enzyme mixture produced methyl 9,10-epoxy stearate. Incubation of linoleic acid alone with a mixture of AsPXG1 and AsLOX2 produced two major epoxy fatty acids, 9,10-epoxy-12-cis-octadecenoic acid and 12,13-epoxy-9-cis-octadecenoic acid, and a minor epoxy fatty acid, probably 12,13-epoxy-9-hydroxy-10-transoctadecenoic acid. AsPXG1 predominately catalyzes intermolecular peroxygenation.

High level accumulation of gamma linolenic acid (C18:3Δ6.9,12 cis) in transgenic safflower (Carthamus tinctorius) seeds

Gamma linolenic acid (GLA; C18:3Δ6,9,12 cis), also known as γ-Linolenic acid, is an important essential fatty acid precursor for the synthesis of very long chain polyunsaturated fatty acids and important pathways involved in human health. GLA is synthesized from linoleic acid (LA; C18:2Δ9,12 cis) by endoplasmic reticulum associated Δ6-desaturase activity. Currently sources of GLA are limited to a small number of plant species with poor agronomic properties, and therefore an economical and abundant commercial source of GLA in an existing crop is highly desirable. To this end, the seed oil of a high LA cultivated species of safflower (Carthamus tinctorius) was modified by transformation with Δ6-desaturase from Saprolegnia diclina resulting in levels exceeding 70% (v/v) of GLA. Levels around 50% (v/v) of GLA in seed oil was achieved when Δ12-/Δ6-desaturases from Mortierella alpina was over-expressed in safflower cultivars with either a high LA or high oleic (OA; C18:1Δ9 cis) background. The differences in the overall levels of GLA suggest the accumulation of the novel fatty acid was not limited by a lack of incorporation into the triacylgylcerol backbone (>66% GLA achieved), or correlated with gene dosage (GLA levels independent of gene copy number), but rather reflected the differences in Δ6-desaturase activity from the two sources. To date, these represent the highest accumulation levels of a newly introduced fatty acid in a transgenic crop. Events from these studies have been propagated and recently received FDA approval for commercialization as Sonova™400.

A P450-centric view of plant evolution

Being by far the largest family of enzymes to support plant metabolism, the cytochrome P450s (CYPs) constitute an excellent reporter of metabolism architecture and evolution. The huge superfamily of CYPs found in angiosperms is built on the successful evolution of 11 ancestral genes, with very different fates and progenies. Essential functions in the production of structural components (membrane sterols), light harvesting (carotenoids) or hormone biosynthesis kept some of them under purifying selection, limiting duplication and sub/neofunctionalization. One group (the CYP71 clan) after an early trigger to diversification, has kept growing, producing bursts of gene duplications at an accelerated rate. The CYP71 clan now represents more than half of all CYPs in higher plants. Such bursts of gene duplication are likely to contribute to adaptation to specific niches and to speciation. They also occur, although with lower frequency, in gene families under purifying selection. The CYP complement (CYPomes) of rice and the model grass weed Brachypodium distachyon have been compared to view evolution in a narrower time window. The results show that evolution of new functions in plant metabolism is a very long-term process. Comparative analysis of the plant CYPomes provides information on the successive steps required for the evolution of land plants, and points to several cases of convergent evolution in plant metabolism. It constitutes a very useful tool for spotting essential functions in plant metabolism and to guide investigations on gene function.

Cytochrome P450 metabolizing fatty acids in plants: characterization and physiological roles

In plants, fatty acids (FA) are subjected to various types of oxygenation reactions. Products include hydroxyacids, as well as hydroperoxides, epoxides, aldehydes, ketones and α,ω-diacids. Many of these reactions are catalysed by cytochrome P450s (P450s), which represent one of the largest superfamilies of proteins in plants. The existence of P450-type metabolizing FA enzymes in plants was established approximately four decades ago in studies on the biosynthesis of lipid polyesters. Biochemical investigations have highlighted two major characteristics of P450s acting on FAs: (a) they can be inhibited by FA analogues carrying an acetylenic function, and (b) they can be enhanced by biotic and abiotic stress at the transcriptional level. Based on these properties, P450s capable of producing oxidized FA have been identified and characterized from various plant species. Until recently, the vast majority of characterized P450s acting on FAs belonged to the CYP86 and CYP94 families. In the past five years, rapid progress in the characterization of mutants in the model plant Arabidopsis thaliana has allowed the identification of such enzymes in many other P450 families (i.e. CYP703, CYP704, CYP709, CYP77, CYP74). The presence in a single species of distinct enzymes characterized by their own regulation and catalytic properties raised the question of their physiological meaning. Functional studies in A. thaliana have demonstrated the involvement of FA hydroxylases in the synthesis of the protective biopolymers cutin, suberin and sporopollenin. In addition, several lines of evidence discussed in this minireview are consistent with P450s metabolizing FAs in many aspects of plant biology, such as defence against pathogens and herbivores, development, catabolism or reproduction.

Mining the bitter melon (momordica charantia l.) seed transcriptome by 454 analysis of non-normalized and normalized cDNA populations for conjugated fatty acid metabolism-related genes

BACKGROUND

Seeds of Momordica charantia (bitter melon) produce high levels of eleostearic acid, an unusual conjugated fatty acid with industrial value. Deep sequencing of non-normalized and normalized cDNAs from developing bitter melon seeds was conducted to uncover key genes required for biotechnological transfer of conjugated fatty acid production to existing oilseed crops. It is expected that these studies will also provide basic information regarding the metabolism of other high-value novel fatty acids.

RESULTS

Deep sequencing using 454 technology with non-normalized and normalized cDNA libraries prepared from bitter melon seeds at 18 DAP resulted in the identification of transcripts for the vast majority of known genes involved in fatty acid and triacylglycerol biosynthesis. The non-normalized library provided a transcriptome profile of the early stage in seed development that highlighted the abundance of transcripts for genes encoding seed storage proteins as well as for a number of genes for lipid metabolism-associated polypeptides, including Δ12 oleic acid desaturases and fatty acid conjugases, class 3 lipases, acyl-carrier protein, and acyl-CoA binding protein. Normalization of cDNA by use of a duplex-specific nuclease method not only increased the overall discovery of genes from developing bitter melon seeds, but also resulted in the identification of 345 contigs with homology to 189 known lipid genes in Arabidopsis. These included candidate genes for eleostearic acid metabolism such as diacylglycerol acyltransferase 1 and 2, and a phospholipid:diacylglycerol acyltransferase 1-related enzyme. Transcripts were also identified for a novel FAD2 gene encoding a functional Δ12 oleic acid desaturase with potential implications for eleostearic acid biosynthesis.

CONCLUSIONS

454 deep sequencing, particularly with normalized cDNA populations, was an effective method for mining of genes associated with eleostearic acid metabolism in developing bitter melon seeds. The transcriptomic data presented provide a resource for the study of novel fatty acid metabolism and for the biotechnological production of conjugated fatty acids and possibly other novel fatty acids in established oilseed crops.

Seed-expressed casein kinase I acts as a positive regulator of the SeFAD2 promoter via phosphorylation of the SebHLH transcription factor

Microsomal oleic acid desaturase (FAD2) catalyzes the first committed step of the biosynthesis of polyunsaturated fatty acids via extra-plastidial desaturation of oleic acid to linoleic acid. In the regulatory mechanism controlling seed-specific SeFAD2 expression, trans-activation of the seed-specific SeFAD2 promoter is mediated by the SebHLH transcription factor (Kim et al. in Plant Mol Biol 64:453-466, 2007). In this study, a protein interacting with SebHLH was isolated from yeast two-hybrid analysis. The protein shares approximately 80% sequence identity with other putative casein kinases and was named SeCKI (Sesame Casein Kinase I). SeCKI transcripts were predominantly expressed in developing sesame seeds and were induced approximately threefold by exogenous application of ABA. eGFP:SeCKI fusion protein was localized to the nucleus. The SeCKI protein specifically bound to SebHLH. The SeCKI protein was autophosphorylated in a calcium-independent manner and transphosphorylated the SebHLH protein. Both the SebHLH and the SeCKI genes or both the SebHLH and mutated SemCKI (K182G) genes, under the control of CaMV 35S promoter, and the GUS reporter gene driven by SeFAD2 promoter containing E- and G-Box motifs were co-expressed in developing sesame seeds. This co-expression revealed that SeCKI enhanced the SebHLH-mediated transactivation of the SeFAD2 gene promoter via phosphorylation of the SebHLH transcription factor.

Seed-expressed casein kinase I acts as a positive regulator of the SeFAD2 promoter via phosphorylation of the SebHLH transcription factor

Microsomal oleic acid desaturase (FAD2) catalyzes the first committed step of the biosynthesis of polyunsaturated fatty acids via extra-plastidial desaturation of oleic acid to linoleic acid. In the regulatory mechanism controlling seed-specific SeFAD2 expression, trans-activation of the seed-specific SeFAD2 promoter is mediated by the SebHLH transcription factor (Kim et al. in Plant Mol Biol 64:453-466, 2007). In this study, a protein interacting with SebHLH was isolated from yeast two-hybrid analysis. The protein shares approximately 80% sequence identity with other putative casein kinases and was named SeCKI (Sesame Casein Kinase I). SeCKI transcripts were predominantly expressed in developing sesame seeds and were induced approximately threefold by exogenous application of ABA. eGFP:SeCKI fusion protein was localized to the nucleus. The SeCKI protein specifically bound to SebHLH. The SeCKI protein was autophosphorylated in a calcium-independent manner and transphosphorylated the SebHLH protein. Both the SebHLH and the SeCKI genes or both the SebHLH and mutated SemCKI (K182G) genes, under the control of CaMV 35S promoter, and the GUS reporter gene driven by SeFAD2 promoter containing E- and G-Box motifs were co-expressed in developing sesame seeds. This co-expression revealed that SeCKI enhanced the SebHLH-mediated transactivation of the SeFAD2 gene promoter via phosphorylation of the SebHLH transcription factor.

Vernonia DGATs increase accumulation of epoxy fatty acids in oil

Vernolic acid (cis-12-epoxy-octadeca-cis-9-enoic acid) is valuable as a renewable chemical feedstock. This fatty acid can accumulate to high levels in the seed oil of some plant species such as Vernonia galamensis and Stokesia laevis which are unsuitable for large-scale production. A cost-effective alternative for production of epoxy fatty acids is to genetically engineer its biosynthesis in commercial oilseeds. An epoxygenase cDNA (SlEPX) responsible for vernolic acid synthesis and two acyl-CoA : diacylglycerol acyltransferase cDNAs (VgDGAT1 and VgDGAT2) catalysing triacylglycerol (TAG) formation were cloned from developing seeds of S. laevis and V. galamensis. Co-expression of SlEPX and VgDGAT1 or VgDGAT2 greatly increases accumulation of vernolic acid both in petunia leaves and soybean somatic embryos. Seed-specific expression of VgDGAT1 and VgDGAT2 in SlEPX mature soybean seeds results in vernolic acid levels of approximately 15% and 26%. Both DGAT1 and DGAT2 increase epoxy fatty acid accumulation with DGAT2 having much greater impact.

DGAT1, DGAT2 and PDAT expression in seeds and other tissues of epoxy and hydroxy fatty acid accumulating plants

Triacylglycerol (TAG) is the main storage lipid in plants. Acyl-CoA: diacylglycerol acyltransferase (DGAT1 and DGAT2) and phospholipid: diacylglycerol acyltransferase (PDAT) can catalyze TAG synthesis. It is unclear how these three independent genes are regulated in developing seeds, and particularly if they have specific functions in the high accumulation of unusual fatty acids in seed oil. The expression patterns of DGAT1, DGAT2 and a PDAT in relation to the accumulation of oil and epoxy and hydroxy fatty acids in developing seeds of the plant species Vernonia galamensis, Euphorbia lagascae, Stokesia laevis and castor that accumulate high levels of these fatty acids in comparison with soybean and Arabidopsis were investigated. The expression patterns of DGAT1, DGAT2 and the PDAT are consistent with all three enzymes playing a role in the high epoxy or hydroxy fatty acid accumulation in developing seeds of these plants. PDAT and DGAT2 transcript levels are present at much higher levels in developing seeds of epoxy and hydroxy fatty acid accumulating plants than in soybeans or Arabidopsis. Moreover, PDAT, DGAT1 and DGAT2 are found to be expressed in many different plant tissues, suggesting that these enzymes may have other roles in addition to seed oil accumulation. DGAT1 appears to be a major enzyme for seed oil accumulation at least in Arabidopsis and soybeans. For the epoxy and hydroxy fatty acid accumulating plants, DGAT2 and PDAT also show expression patterns consistent with a role in the selective accumulation of these unusual fatty acids in seed oil.

Changes in oil content of transgenic soybeans expressing the yeast SLC1 gene

The wild type (Wt) and mutant form of yeast (sphingolipid compensation) genes, SLC1 and SLC1-1, have been shown to have lysophosphatidic acid acyltransferase (LPAT) activities (Nageic et al. in J Biol Chem 269:22156-22163, 1993). Expression of these LPAT genes was reported to increase oil content in transgenic Arabidopsis and Brassica napus. It is of interest to determine if the TAG content increase would also be seen in soybeans. Therefore, the wild type SLC1 was expressed in soybean somatic embryos under the control of seed specific phaseolin promoter. Some transgenic somatic embryos and in both T2 and T3 transgenic seeds showed higher oil contents. Compared to controls, the average increase in triglyceride values went up by 1.5% in transgenic somatic embryos. A maximum of 3.2% increase in seed oil content was observed in a T3 line. Expression of the yeast Wt LPAT gene did not alter the fatty acid composition of the seed oil.

CYP86B1 is required for very long chain omega-hydroxyacid and alpha, omega -dicarboxylic acid synthesis in root and seed suberin polyester

Suberin composition of various plants including Arabidopsis (Arabidopsis thaliana) has shown the presence of very long chain fatty acid derivatives C20 in addition to the C16 and C18 series. Phylogenetic studies and plant genome mining have led to the identification of putative aliphatic hydroxylases belonging to the CYP86B subfamily of cytochrome P450 monooxygenases. In Arabidopsis, this subfamily is represented by CYP86B1 and CYP86B2, which share about 45% identity with CYP86A1, a fatty acid omega-hydroxylase implicated in root suberin monomer synthesis. Here, we show that CYP86B1 is located to the endoplasmic reticulum and is highly expressed in roots. Indeed, CYP86B1 promoter-driven beta-glucuronidase expression indicated strong reporter activities at known sites of suberin production such as the endodermis. These observations, together with the fact that proteins of the CYP86B type are widespread among plant species, suggested a role of CYP86B1 in suberin biogenesis. To investigate the involvement of CYP86B1 in suberin biogenesis, we characterized an allelic series of cyp86B1 mutants of which two strong alleles were knockouts and two weak ones were RNA interference-silenced lines. These root aliphatic plant hydroxylase lines had a root and a seed coat aliphatic polyester composition in which C22- and C24-hydroxyacids and alpha,omega-dicarboxylic acids were strongly reduced. However, these changes did not affect seed coat permeability and ion content in leaves. The presumed precursors, C22 and C24 fatty acids, accumulated in the suberin polyester. These results demonstrate that CYP86B1 is a very long chain fatty acid hydroxylase specifically involved in polyester monomer biosynthesis during the course of plant development.

Identification of a potential bottleneck in branched chain fatty acid incorporation into triacylglycerol for lipid biosynthesis in agronomic plants

In plant, unusual fatty acids are produced by a limited number of species. The industrial benefits of these unusual structures have led several groups to study their production in transgenic plants. Their research results led to very modest accumulation in seeds which was largely due to a limited knowledge of the lipid metabolism and fatty acid transfer in plants. More specifically we need to better understand the substrate specificity and selectivity of acyltransferases which are required for the incorporation of these unusual fatty acids into storage triacylglycerols. In our studies we have compared the incorporation of [(14)C] Oleoyl-CoA and Branched Chain Acyls-CoA into [(3)H] LPA-C18:1 by the Lysophosphatidic acid Acyltransferase (LPAAT) from developing seeds of agronomic plants (flax (Linum usitatissimum) and rape (Brassica napus)) and from a plant capable of producing high amounts of hydroxy fatty acids (castor bean (Ricinus communis)). Our assays demonstrate that LPAATs of the three studied species (1) incorporated preferentially oleyl-CoA, (2) could incorporate cyclopropane acyl-CoA when added alone as a substrate, however very weakly for rapeseed and castor bean seeds, (3) presented a low capacity to incorporate methyl branched acyl-CoA when added alone as a substrate (4) weakly incorporated cyclopropane acyl-CoA and was unable to incorporate methyl branched acyl-CoA when presented with an equimolar mix of oleyl-CoA and branched chain acyl-CoA. In all cases, the LPAAT had a low affinity for branched chain acyl-CoAs. The results show that LPAAT activity from agronomic plants constitutes a bottleneck for the incorporation of branched Chain acyl-CoA into PA.

CYP86A33-targeted gene silencing in potato tuber alters suberin composition, distorts suberin lamellae, and impairs the periderm's water barrier function

Suberin is a cell wall lipid polyester found in the cork cells of the periderm offering protection against dehydration and pathogens. Its biosynthesis and assembly, as well as its contribution to the sealing properties of the periderm, are still poorly understood. Here, we report on the isolation of the coding sequence CYP86A33 and the molecular and physiological function of this gene in potato (Solanum tuberosum) tuber periderm. CYP86A33 was down-regulated in potato plants by RNA interference-mediated silencing. Periderm from CYP86A33-silenced plants revealed a 60% decrease in its aliphatic suberin load and greatly reduced levels of C18:1 omega-hydroxyacid (approximately 70%) and alpha,omega-diacid (approximately 90%) monomers in comparison with wild type. Moreover, the glycerol esterified to suberin was reduced by 60% in the silenced plants. The typical regular ultrastructure of suberin, consisting of dark and light lamellae, disappeared and the thickness of the suberin layer was clearly reduced. In addition, the water permeability of the periderm isolated from CYP86A33-silenced lines was 3.5 times higher than that of the wild type. Thus, our data provide convincing evidence for the involvement of omega-functional fatty acids in establishing suberin structure and function.

Arabidopsis thaliana CYP77A4 is the first cytochrome P450 able to catalyze the epoxidation of free fatty acids in plants

An approach based on an in silico analysis predicted that CYP77A4, a cytochrome P450 that so far has no identified function, might be a fatty acid-metabolizing enzyme. CYP77A4 was heterologously expressed in a Saccharomyces cerevisiae strain (WAT11) engineered for cytochrome P450 expression. Lauric acid (C(12:0)) was converted into a mixture of hydroxylauric acids when incubated with microsomes from yeast expressing CYP77A4. A variety of physiological C(18) fatty acids were tested as potential substrates. Oleic acid (cis-Delta(9)C(18:1)) was converted into a mixture of omega-4- to omega-7-hydroxyoleic acids (75%) and 9,10-epoxystearic acid (25%). Linoleic acid (cis,cis-Delta(9),Delta(12)C(18:2)) was exclusively converted into 12,13-epoxyoctadeca-9-enoic acid, which was then converted into diepoxide after epoxidation of the Delta(9) unsaturation. Chiral analysis showed that 9,10-epoxystearic acid was a mixture of 9S/10R and 9R/10S in the ratio 33 : 77, whereas 12,13-epoxyoctadeca-9-enoic acid presented a strong enantiomeric excess in favor of 12S/13R, which represented 90% of the epoxide. Neither stearic acid (C(18:0)) nor linolelaidic acid (trans,trans-Delta(9),Delta(12)C(18:2)) was metabolized, showing that CYP77A4 requires a double bond, in the cis configuration, to metabolize C(18) fatty acids. CYP77A4 was also able to catalyze the in vitro formation of the three mono-epoxides of alpha-linolenic acid (cis,cis,cis-Delta(9),Delta(12),Delta(15)C(18:3)), previously described as antifungal compounds. Epoxides generated by CYP77A4 are further metabolized to the corresponding diols by epoxide hydrolases located in microsomal and cytosolic subcellular fractions from Arabidopsis thaliana. The concerted action of CYP77A4 with epoxide hydrolases and hydroxylases allows the production of compounds involved in plant-pathogen interactions, suggesting a possible role for CYP77A4 in plant defense.

Building lipid barriers: biosynthesis of cutin and suberin

Cutin and suberin are the polymer matrices for lipophilic cell wall barriers. These barriers control the fluxes of gases, water and solutes, and also play roles in protecting plants from biotic and abiotic stresses and in controlling plant morphology. Although they are ubiquitous, cutin and suberin are the least understood of the major plant extracellular polymers. The use of forward and reverse genetic approaches in Arabidopsis has led to the identification of oxidoreductase and acyltransferase genes involved in the biosynthesis of these polymers. However, major questions about the underlying polymer structure, biochemistry, and intracellular versus extracellular assembly remain to be resolved. The analysis of plant lines with modified cutins and suberins has begun to reveal the inter-relationships between the composition and function of these polymers.

Metabolic engineering of natural products in plants; tools of the trade and challenges for the future

Plant natural products play essential roles in plant survivability and many of them are used as nutrients, colorants, flavors, fragrances, and medicines. Genetic engineering of plants for natural products can help alleviate the demands for limited natural resources. Successes in enhancing production capacities have included manipulating blocks of genes coding for segments of pathways, over-expression of putative rate-limiting steps in pathways, expression of transcription factors regulating the entire metabolic pathways, and the construction of novel branch pathways capable of diverting carbon to the biosynthesis of unique metabolites in unexpected intracellular compartments. Further enhancements are likely if more efficient pathways can be constructed, providing for the efficient channeling of intermediates to final products, and if the means for sequestering natural products in planta can be accomplished.

Genetic contributions to agricultural sustainability

The current tools of enquiry into the structure and operation of the plant genome have provided us with an understanding of plant development and function far beyond the state of knowledge that we had previously. We know about key genetic controls repressing or stimulating the cascades of gene expression that move a plant through stages in its life cycle, facilitating the morphogenesis of vegetative and reproductive tissues and organs. The new technologies are enabling the identification of key gene activity responses to the range of biotic and abiotic challenges experienced by plants. In the past, plant breeders produced new varieties with changes in the phases of development, modifications of plant architecture and improved levels of tolerance and resistance to environmental and biotic challenges by identifying the required phenotypes in a few plants among the large numbers of plants in a breeding population. Now our increased knowledge and powerful gene sequence-based diagnostics provide plant breeders with more precise selection objectives and assays to operate in rationally planned crop improvement programmes. We can expect yield potential to increase and harvested product quality portfolios to better fit an increasing diversity of market requirements. The new genetics will connect agriculture to sectors beyond the food, feed and fibre industries; agri-business will contribute to public health and will provide high-value products to the pharmaceutical industry as well as to industries previously based on petroleum feedstocks and chemical modification processes.