Unraveling Reciprocal Lipid-Mediated Communication between Maize Seed and Aspergillus flavus

It is generally accepted, that the reciprocal exchange of molecules between plants and fungi govern the outcome of their interaction. From a multitude of potential signals, one class of oxidized lipids (oxylipins) has taken central stage in this concept. Synthesized from enzymatic and non-enzymatic peroxidation of fatty acids, oxylipins are a large and diverse group of potent endogenous signaling molecules. Because plant and fungal oxylipins are similar biochemically and structurally, a novel hypothesis has emerged that during plant-fungal interactions, that these metabolites are exchanged, perceived, and affect the behavior of opposing partner. This study sought to explore this hypothesis and assign a role to specific oxylipin-producing enzymes from maize and Aspergillus flavus within the context of the oxylipin-mediated cross-kingdom crosstalk. Maize wild-type and near-isogenic mutants for several lipoxygenase (LOX) and 12-oxophytodienoate reductases (OPR) related to jasmonic acid biosynthesis and nine oxylipin-mutant strains of Aspergillus flavus were utilized to investigate the contribution of oxylipins from the plant and the fungi on fungal ability to colonize the host, sporulate and produce aflatoxin. Phytohormone content and gene expression analyses of infected seed were preformed to explore potential associations of defense hormones with fungal pathogenesis processes. Results showed that several genes involved in JA biosynthesis affect specific fungal processes. Despite belonging to separate subgroups, both LOX3 and LOX7 are involved in defense against colonization. Additionally, LOX3 expression correlates negatively with colonization and lox3 knockout mutants are more susceptible regardless of the fungal genotype indicating a general defensive role for LOX3 against A. flavus colonization. An unexpected major finding from this study is that JA biosynthesis genes appear to promote aflatoxin accumulation. Results provide evidence that the fungal LOX gene is required for normal colonization of seed, while PpoA is required for normal conidia and aflatoxin production. The ratio of ABA/JA correlates positively with aflatoxin accumulation. These findings are expected to expedite studies of seed-fungal interactions, lead to uncovering novel regulators of seed defense, find specific host genes and signals that regulate conidiation and mycotoxin production, and eventually provide the maize industry with genetic targets and biochemical markers for selecting aflatoxin resistant lines

Synthesis and Functions of Jasmonates in Maize

Of the over 600 oxylipins present in all plants, the phytohormone jasmonic acid (JA) remains the best understood in terms of its biosynthesis, function and signaling. Much like their eicosanoid analogues in mammalian system, evidence is growing for the role of the other oxylipins in diverse physiological processes. JA serves as the model plant oxylipin species and regulates defense and development. For several decades, the biology of JA has been characterized in a few dicot species, yet the function of JA in monocots has only recently begun to be elucidated. In this work, the synthesis and function of JA in maize is presented from the perspective of oxylipin biology. The maize genes responsible for catalyzing the reactions in the JA biosynthesis are clarified and described. Recent studies into the function of JA in maize defense against insect herbivory, pathogens and its role in growth and development are highlighted. Additionally, a list of JA-responsive genes is presented for use as biological markers for improving future investigations into JA signaling in maize

Oxylipin biosynthetic gene families of Cannabis sativa.

Cannabis sativa is a global multi-billion-dollar cash crop with numerous industrial uses, including in medicine and recreation where its value is largely owed to the production of pharmacological and psychoactive metabolites known as cannabinoids. Often underappreciated in this role, the lipoxygenase (LOX)-derived green leaf volatiles (GLVs), also known as the scent of cut grass, are the hypothetical origin of hexanoic acid, the initial substrate for cannabinoid biosynthesis. The LOX pathway is best known as the primary source of plant oxylipins, molecules analogous to the eicosanoids from mammalian systems. These molecules are a group of chemically and functionally diverse fatty acid-derived signals that govern nearly all biological processes including plant defense and development. The interaction between oxylipin and cannabinoid biosynthetic pathways remains to be explored. Despite their unique importance in this crop, there has not been a comprehensive investigation focusing on the genes responsible for oxylipin biosynthesis in any Cannabis species. This study documents the first genome-wide catalogue of the Cannabis sativa oxylipin biosynthetic genes and identified 21 LOX, five allene oxide synthases (AOS), three allene oxide cyclases (AOC), one hydroperoxide lyase (HPL), and five 12-oxo-phytodienoic acid reductases (OPR). Gene collinearity analysis found chromosomal regions containing several isoforms maintained across Cannabis, Arabidopsis, and tomato. Promoter, expression, weighted co-expression genetic network, and functional enrichment analysis provide evidence of tissue- and cultivar-specific transcription and roles for distinct isoforms in oxylipin and cannabinoid biosynthesis. This knowledge facilitates future targeted approaches towards Cannabis crop improvement and for the manipulation of cannabinoid metabolism

Oxylipin biosynthetic gene families of Cannabis sativa

Cannabis sativa is a global multi-billion-dollar cash crop with numerous industrial uses, including in medicine and recreation where its value is largely owed to the production of pharmacological and psychoactive metabolites known as cannabinoids. Often underappreciated in this role, the lipoxygenase (LOX)-derived green leaf volatiles (GLVs), also known as the scent of cut grass, are the hypothetical origin of hexanoic acid, the initial substrate for cannabinoid biosynthesis. The LOX pathway is best known as the primary source of plant oxylipins, molecules analogous to the eicosanoids from mammalian systems. These molecules are a group of chemically and functionally diverse fatty acid-derived signals that govern nearly all biological processes including plant defense and development. The interaction between oxylipin and cannabinoid biosynthetic pathways remains to be explored. Despite their unique importance in this crop, there has not been a comprehensive investigation focusing on the genes responsible for oxylipin biosynthesis in any Cannabis species. This study documents the first genome-wide catalogue of the Cannabis sativa oxylipin biosynthetic genes and identified 21 LOX, five allene oxide synthases (AOS), three allene oxide cyclases (AOC), one hydroperoxide lyase (HPL), and five 12-oxo-phytodienoic acid reductases (OPR). Gene collinearity analysis found chromosomal regions containing several isoforms maintained across Cannabis, Arabidopsis, and tomato. Promoter, expression, weighted co-expression genetic network, and functional enrichment analysis provide evidence of tissue- and cultivar-specific transcription and roles for distinct isoforms in oxylipin and cannabinoid biosynthesis. This knowledge facilitates future targeted approaches towards Cannabis crop improvement and for the manipulation of cannabinoid metabolism

Arctic marine fungi: biomass, functional genes, and putative ecological roles

Recent molecular evidence suggests a global distribution of marine fungi; however, the ecological relevance and corresponding biological contributions of fungi to marine ecosystems remains largely unknown. We assessed fungal biomass from the open Arctic Ocean by applying novel biomass conversion factors from cultured isolates to environmental sterol and CARD-FISH data. We found an average of 16.54 nmol m−3 of ergosterol in sea ice and seawater, which corresponds to 1.74 mg C m−3 (444.56 mg C m−2 in seawater). Using Chytridiomycota-specific probes, we observed free-living and particulate-attached cells that averaged 34.07 µg C m−3 in sea ice and seawater (11.66 mg C m−2 in seawater). Summed CARD-FISH and ergosterol values approximate 1.77 mg C m−3 in sea ice and seawater (456.23 mg C m−2 in seawater), which is similar to biomass estimates of other marine taxa generally considered integral to marine food webs and ecosystem processes. Using the GeoChip microarray, we detected evidence for fungal viruses within the Partitiviridae in sediment, as well as fungal genes involved in the degradation of biomass and the assimilation of nitrate. To bridge our observations of fungi on particulate and the detection of degradative genes, we germinated fungal conidia in zooplankton fecal pellets and germinated fungal conidia after 8 months incubation in sterile seawater. Ultimately, these data suggest that fungi could be as important in oceanic ecosystems as they are in freshwater environments

Phylogenetic, genetic, motif, and domain analysis of the CsAOC gene family.

(A) Cladogram of peptide sequences and conserved domains. (B) Distribution of conserved peptide sequence motifs. Colors are described in legend; x-axis represents length of peptides in amino acids. (C) Diagram of genetic structure. Blue bars, orange bars, and gray lines represent untranslated regions, exons, and introns, respectively; x-axis represents length of gene in nucleotides. (D) Polar cladogram depicting evolutionary relationship with gene families of selected species. Node labels show confidence values from 1000 bootstrap replications.</p

Phylogenetic, genetic, motif, and domain analysis of the CsLOX gene family.

(A) Cladogram of peptide sequences and conserved domains. (B) Distribution of conserved peptide sequence motifs. Colors are described in legend; x-axis represents length of peptides in amino acids. (C) Diagram of genetic structure. Blue bars, orange bars, and gray lines represent untranslated regions, exons, and introns, respectively; x-axis represents length of gene in nucleotides. (D) Polar cladogram depicting evolutionary relationship with gene families of selected species. Node labels show confidence values from 1000 bootstrap replications.</p

Regions of duplicated <i>OPR</i>, <i>AOS</i>, and <i>AOC</i> genes on <i>C</i>. <i>sativa</i> Chromosomes 1, 8, and X.

Regions of duplicated OPR, AOS, and AOC genes on C. sativa Chromosomes 1, 8, and X.</p