Molecular details of secretory phospholipase A2 from flax (Linum usitatissimum L.) provide insight into its structure and function

Biotechnological advances in the production of unusual fatty acids in transgenic plants and recombinant microorganisms

Certain plants and microorganisms can produce high amounts of unusual fatty acids (UFAs) such as hydroxy, conjugated, cyclic, and very long-chain polyunsaturated fatty acids, which have distinct physicochemical properties and significant applications in the food, feed, and oleochemical industries. Since many natural sources of UFAs are not ideal for large-scale agricultural production or fermentation, it is attractive to produce them through synthetic biology. Although several UFAs have been commercially or pre-commercially produced in transgenic plants and microorganisms, their contents in transgenic hosts are generally much lower than in natural sources. Moreover, reproducing this success for a wider spectrum of UFAs has remained challenging. This review discusses recent advancements in our understanding of the biosynthesis, accumulation, and heterologous production of UFAs, and addresses the challenges and potential strategies for achieving high UFA content in engineered plants and microorganisms.

Phylogenomic Analysis of micro-RNA Involved in Juvenile to Flowering-Stage Transition in Photophilic Rice and Its Sister Species

Vegetative to reproductive phase transition in phototropic plants is an important developmental process and is sequentially mediated by the expression of micro-RNA MIR172. To obtain insight into the evolution, adaptation, and function of MIR172 in photophilic rice and its wild relatives, we analyzed the genescape of a 100 kb segment harboring MIR172 homologs from 11 genomes. The expression analysis of MIR172 revealed its incremental accumulation from the 2-leaf to 10-leaf stage, with maximum expression coinciding with the flag-leaf stage in rice. Nonetheless, the microsynteny analysis of MIR172s revealed collinearity within the genus Oryza, but a loss of synteny was observed in (i) MIR172A in O. barthii (AA) and O. glaberima (AA); (ii) MIR172B in O. brachyantha (FF); and (iii) MIR172C in O. punctata (BB). Phylogenetic analysis of precursor sequences/region of MIR172 revealed a distinct tri-modal clade of evolution. The genomic information generated in this investigation through comparative analysis of MIRNA, suggests mature MIR172s to have evolved in a disruptive and conservative mode amongst all Oryza species with a common origin of descent. Further, the phylogenomic delineation provided an insight into the adaptation and molecular evolution of MIR172 to changing environmental conditions (biotic and abiotic) of phototropic rice through natural selection and the opportunity to harness untapped genomic regions from rice wild relatives (RWR).

Comparative phylogenomic and structural analysis of canonical secretory PLA2 and novel PLA2-like family in plants

Plant secretory phospholipase A₂ (sPLA₂) is a family of lipolytic enzymes involved in the sn-2 hydrolysis of phospholipid carboxyester bonds, characterized by the presence of a conserved PA2c domain. PLA₂ produces free fatty acids and lysophospholipids, which regulate several physiological functions, including lipid metabolism, plant growth and development, signal transduction, and response to various environmental stresses. In the present work, we have performed a comparative analysis of PA2c domain-containing genes across plants, focusing on gene distribution, phylogenetic analysis, tissue-specific expression, and homology modeling. Our data revealed the widespread occurrence of multiple sPLA₂ in most land plants and documented single sPLA₂ in multiple algal groups, indicating an ancestral origin of sPLA₂. We described a novel PA2c-containing gene family present in all plant lineages and lacking secretory peptide, which we termed PLA₂-like. Phylogenetic analysis revealed two independent clades in canonical sPLA₂ genes referred to as α and β clades, whereas PLA₂-like genes clustered independently as a third clade. Further, we have explored clade-specific gene expressions showing that while all three clades were expressed in vegetative and reproductive tissues, only sPLA₂-β and PLA₂-like members were expressed in the pollen and pollen tube. To get insight into the conservation of the gene regulatory network of sPLA₂ and PLA₂-like genes, we have analyzed the occurrence of various cis-acting promoter elements across the plant kingdom. The comparative 3D structure analysis revealed conserved and unique features within the PA2c domain for the three clades. Overall, this study will help to understand the evolutionary significance of the PA2c family and lay the foundation for future sPLA₂ and PLA₂-like characterization in plants.

A secretory phospholipase A2 of a fungal pathogen contributes to lipid droplet homeostasis, assimilation of insect-derived lipids, and repression of host immune responses

Secretory phospholipase A2s (sPLA2s) are found in a wide range of organisms from bacteria to higher plants and animals and are involved in varied and cellular processes. However, roles of these enzymes in microbial pathogens remain unclear. Here, an sPLA2 (BbPLA2) was characterized in the filamentous insect pathogenic fungus, Beauveria bassiana. BbPLA2 was exclusively expressed in insect hemolymph-derived cells (hyphal bodies), and its expression was induced by insect-derived nutrients and lipids, and nutrient starvation. High levels of secretion of BbPLA2 were observed as well as its distribution in hyphal body lipid drops (LDs). Overexpression of BbPLA2 increased the ability of B. bassiana to utilize insect-derived nutrients and lipids, and promoted LD accumulation, indicating functions for BbPLA2 in mediating LD homeostasis and assimilation of insect-derived lipids. Strains overexpressing BbPLA2 showed moderately increased virulence, including more efficient penetration of the insect cuticle and evasion of host immune responses as compared to the wild type strain. In addition, B. bassiana-activated host immune genes were downregulated in the BbPLA2 overexpression strain, but upregulated by infections with a ΔBbPLA2 strain. These data demonstrate that BbPLA2 contributes to LD homeostasis, assimilation of insect-derived lipids, and repression of host immune responses.

Analysis of Homologous Regions of Small RNAs MIR397 and MIR408 Reveals the Conservation of Microsynteny among Rice Crop-Wild Relatives

MIRNAs are small non-coding RNAs that play important roles in a wide range of biological processes in plant growth and development. MIR397 (involved in drought, low temperature, and nitrogen and copper (Cu) starvation) and MIR408 (differentially expressed in response to environmental stresses such as copper, light, mechanical stress, dehydration, cold, reactive oxygen species, and drought) belong to conserved MIRNA families that either negatively or positively regulate their target genes. In the present study, we identified the homologs of MIR397 and MIR408 in Oryza sativa and its six wild progenitors, three non-Oryza species, and one dicot species. We analyzed the 100 kb segments harboring MIRNA homologs from 11 genomes to obtain a comprehensive view of their community evolution around these loci in the farthest (distant) relatives of rice. Our study showed that mature MIR397 and MIR408 were highly conserved among all Oryza species. Comparative genomics analyses also revealed that the microsynteny of the 100 kb region surrounding MIRNAs was only conserved in Oryza spp.; disrupted in Sorghum, maize, and wheat; and completely lost in Arabidopsis. There were deletions, rearrangements, and translocations within the 100 kb segments in Oryza spp., but the overall microsynteny of the region was maintained. The phylogenetic analyses of the precursor regions of all MIRNAs under study revealed a bimodal clade of common origin. This comparative analysis of miRNA involved in abiotic stress tolerance in plants provides a powerful tool for future Oryza research. Crop wild relatives (CWRs) offer multiple traits with potential to decrease the amount of yield loss owing to biotic and abiotic stresses. Using a comparative genomics approach, the exploration of CWRs as a source of tolerance to these stresses by understanding their evolution can be further used to leverage their yield potential.

Formation Mechanism of Hexanal and (E)-2-Hexenal during Soybean [Glycine max (L.) Merr] Processing Based on the Subcellular and Molecular Levels

Hexanal and (E)-2-hexenal in soymilk mainly form during the soaking and grinding of soybeans. In this study, freshly dehulled soybeans were soaked or ground in the presence or absence of different enzyme inhibitors. The results showed that (1) 1-palmitoyl-2-linoleoyl-sn-3-phosphatidylcholine, 1-stearoyl-2-linoleoyl-sn-3-phosphatidylcholine, 1-palmitoyl-2-linolenoyl-sn-3-phosphatidylcholine, and 1-stearoyl-2-linolenoyl-sn-3-phosphatidylcholine were preferentially acted upon by lipoxygenases (LOXs) and made predominant contributions to hexanal/(E)-2-hexenal formation. Phospholipase A2 (PLA2) is one of the key enzymes for hexanal/(E)-2-hexenal formation. (2) The ratio of net increase in hexanal/(E)-2-hexenal and net decrease in linoleic acid/linolenic acid was close to 100% during soaking, but it was only 60% during grinding. Only 13-hydroperoxy octadecad(tr)ienoic acid (13-HPOD/T) was formed for the membrane LOX, but both 13- and 9-hydroperoxy octadecad(tr)ienoic acid (9-HPOD/T) were produced for the cytoplasm LOX. Thus, only the membrane LOX was involved during soaking, while both membrane- and cytoplasm-bound LOXs worked during grinding. (3) Hydroperoxides and hexanal/(E)-2-hexenal during soybean grinding were studied. PC hydroperoxides formed almost instantly and reached a maximum in 10 s, while fatty acid hydroperoxides and hexanal/(E)-2-hexenal formed relatively slowly and reached a maximum in 50 s. The experimental data were fitted to the integrated form of the Michaelis-Menten equation, and Km, Vmax, and kcat for the LOX, PLA2, and hydroperoxide lyase were obtained, respectively.

Secreted Phospholipases A2 - not just Enzymes: Revisited

Secreted phospholipases A₂ (sPLA₂s) participate in a very broad spectrum of biological processes through their enzymatic activity and as ligands for membrane and soluble receptors. The physiological roles of sPLA₂s as enzymes have been very well described, while their functions as ligands are still poorly known. Since the last overview of sPLA₂-binding proteins (sPLA₂-BPs) 10 years ago, several important discoveries have occurred in this area. New and more sensitive analytical tools have enabled the discovery of additional sPLA₂-BPs, which are presented and critically discussed here. The structural diversity of sPLA₂-BPs reveals sPLA₂s as very promiscuous proteins, and we offer some structural explanations for this nature that makes these proteins evolutionarily highly advantageous. Three areas of physiological engagement of sPLA₂-BPs have appeared most clearly: cellular transport and signalling, and regulation of the enzymatic activity of sPLA₂s. Due to the multifunctionality of sPLA₂s, they appear to be exceptional pharmacological targets. We reveal the potential to exploit interactions of sPLA₂s with other proteins in medical terms, for the development of original diagnostic and therapeutic procedures. We conclude this survey by suggesting the priority questions that need to be answered.

Green revolution to grain revolution: Florigen in the frontiers

Burgeoning human population dents, globally, the brimming buffer stock as well as gain in food grain production. However, an imminent global starvation was averted through precise scientific intervention and pragmatic policy changes in the 1960s and was eulogized as the "Green Revolution". Miracle rice and wheat obtained through morphometric changes in the ideotype of these two crops yielded bumper harvest that nucleated in Asia and translated into Latin America. The altered agronomic traits in these two crops were the result of tinkering with the phyto-hormone "Gibberellin'. Recently, another plant hormone 'Cytokinin' has gained prominence for its involvement in the grain revolution in rice and other field crops. Suo moto homeostasis of CK by the cytokinin oxidase enzyme governs the cardinal shoot apical meristem that produces new flowering primordia thereby enhancing grain number. Similarly, the flowering hormone 'Florigen' impacts sympodia formation, flowering, and fruit production in tomato. The role of heterozygosity induced heterosis by florigen in revolutionizing tomato production and cellular homeostasis of CK by CK oxidising enzyme (CKX) in enhancing rice production has been path-breaking. This review highlights role of phytohormones in grain revolution and crop specific fine-tuning of gibberellins, cytokinins and florigen to accomplish maximum yield potential in field crops.

Ex-foliar application of glycine betaine and its impact on protein, carbohydrates and induction of ROS scavenging system during drought stress in flax (Linum usitatissimum)

Crop plants have an innate capacity to acclimatize and survive myriad stresses in field conditions. This acclimatization to stress enhances crop stand in field and productivity of plant. Inter alia field crops withstand drought stress (hydropenia) by inducing synthesis or accumulation of osmolytes such as (i) proline and other amino acids, (ii) glycine betaine (GB), (iii) soluble carbohydrates, and (iv) reactive oxygen species (ROS) scavenging system as intrinsic drought antagonizing molecules. Precise in vivo induction of osmolytes and their effect on ROS scavenging system in flax/linseed has not been elucidated. The investigation was carried out to identify a tolerant and susceptible cultivar of flax from a core collection of 53 core accessions and evaluate the role of compatible osmolytes in Linum usitatissimum under hydropenia. We screened eight morphometrically diverse flax genotypes in field under irrigated and un-irrigated condition and classified them as tolerant and susceptible genotypes. Further, we examined the effect of ex-foliar glycine betaine application - a signature molecule involved in drought tolerance, on selected tolerant and susceptible varieties. Our results showed stimulatory impact of glycine betaine on accumulation of ROS scavenging antioxidants, total soluble protein and on its own accumulation. While the ex-foliar application had no inhibitory effect on the growth of plants; accumulation of free proline, amino acids and carbohydrates are inhibited par se in flax. Our findings reveal, flax is a non-accumulator of glycine betaine and exogenous application of glycine betaine enhances its own levels during drought stress.

Genome-wide identification and expression analysis of the WRKY transcription factor family in flax (Linum usitatissimum L.)

BACKGROUND

Members of the WRKY protein family, one of the largest transcription factor families in plants, are involved in plant growth and development, signal transduction, senescence, and stress resistance. However, little information is available about WRKY transcription factors in flax (Linum usitatissimum L.).

RESULTS

In this study, comprehensive genome-wide characterization of the flax WRKY gene family was conducted that led to prediction of 102 LuWRKY genes. Based on bioinformatics-based predictions of structural and phylogenetic features of encoded LuWRKY proteins, 95 LuWRKYs were classified into three main groups (Group I, II, and III); Group II LuWRKYs were further assigned to five subgroups (IIa-e), while seven unique LuWRKYs (LuWRKYs 96-102) could not be assigned to any group. Most LuWRKY proteins within a given subgroup shared similar motif compositions, while a high degree of motif composition variability was apparent between subgroups. Using RNA-seq data, expression patterns of the 102 predicted LuWRKY genes were also investigated. Expression profiling data demonstrated that most genes associated with cellulose, hemicellulose, or lignin content were predominantly expressed in stems, roots, and less in leaves. However, most genes associated with stress responses were predominantly expressed in leaves and exhibited distinctly higher expression levels in developmental stages 1 and 8 than during other stages.

CONCLUSIONS

Ultimately, the present study provides a comprehensive analysis of predicted flax WRKY family genes to guide future investigations to reveal functions of LuWRKY proteins during plant growth, development, and stress responses.

An Apical Meristem-Targeted in planta Transformation Method for the Development of Transgenics in Flax (Linum usitatissimum): Optimization and Validation

Efficient regeneration of explants devoid of intrinsic somaclonal variations is a cardinal step in plant tissue culture, thus, a vital component of transgenic technology. However, recalcitrance of economically important crops to tissue culture-based organogenesis ensues a setback in the use of transgenesis in the genetic engineering of crop plants. The present study developed an optimized, genotype-independent, nonconventional tissue culture-independent in planta strategy for the genetic transformation of flax/linseed. This apical meristem-targeted in planta transformation protocol will accelerate value addition in the dual purpose industrially important but recalcitrant fiber crop flax/linseed. The study delineated optimization of Agrobacterium tumefaciens-mediated transformation and stable T-DNA (pCambia2301:GUS:nptII) integration in flax. It established successful use of a stringent soilrite-based screening in the presence of 30 mg/L kanamycin for the identification of putative transformants. The amenability, authenticity, and reproducibility of soilrite-based kanamycin screening were further verified at the molecular level by GUS histochemical analysis of T₀ seedlings, GUS and nptII gene-specific PCR, genomic Southern hybridization for stable integration of T-DNA, and expression analysis of transgenes by sqRT-PCR. This method resulted in a screening efficiency of 6.05% in the presence of kanamycin, indicating amenability of in planta flax transformation. The strategy can be a promising tool for the successful development of transgenics in flax.