Biology subjects

Jander, G.

Publications and source records attributed to Jander, G..

At least 19 recordsLinked to original sources

bioRxiv2026

An Aphid Protein Interferes with Plant endomembrane Trafficking Machinery to Promote Aphid Survival and Plant Growth

Aphids deplete their host plants of amino acids and other essential nutrients by feeding on phloem sap. Autophagy, a conserved process across eukaryotes, maintains cellular homeostasis during starvation and environmental stress by recycling damaged or excess cellular components. Here, we identified and characterized a previously uninvestigated aphid salivary protein, termed Aphid Autophagy Related Factor 1 (AAF1), that is secreted into plant cells and manipulates plant physiology in a manner that benefits the aphid. We show that AAF1 interacts with four known or putative host autophagy related proteins: RABD1 and RABD2a (plant homologs of Ypt1/RAB1), ATG8, a ubiquitin like protein required for autophagosome formation, and PI3PT, a previously uncharacterized ER localized putative lipid binding or lipid transfer protein annotated as a phosphoinositide 3 phosphate transfer protein. We further demonstrate that the RAB binding domain of AAF1 and its interaction with RABD2a may be specifically required for AAF1 function. In addition, we identified unique, highly mobile compartments containing interacting AAF1 and RABD2a that are associated with the endoplasmic reticulum (ER) and dynamically traffic with autophagosomes. We propose that these compartments may be derived from endosomes or endosome to ER contact sites (EERCSs) and serve as platforms for autophagosome trafficking and/or biogenesis. We further propose that AAF1, RABD2a, and PI3PT function together to regulate the formation or function of these compartments, thereby supporting autophagosome formation and trafficking. Finally, we show that stable expression of AAF1 in plants enhances growth and biomass in an autophagy dependent manner.

plant biology↗

bioRxiv2026

Host insect microRNAs are translocated to an obligate endosymbiont

Many insects rely on intimate interactions with bacterial symbionts housed in specialized cells called bacteriocytes. While host and symbiont gene expression in bacteriocytes appears highly integrated, the underlying regulatory mechanisms remain largely unknown. MicroRNAs regulate gene expression and are emerging as mediators of cross-kingdom communication. Here, in the pea aphid, Acyrthosiphon pisum, and the green peach aphid, Myzus persicae, we demonstrate cross-kingdom translocation of aphid miRNAs into their obligate endosymbiont, Buchnera aphidicola. miRNA fluorescence in situ hybridization in aphid embryos provides direct evidence that four out of five candidate miRNAs (miR-1, miR-10, miR-29, and miR-927) localize inside Buchnera cells. To investigate how these miRNAs may regulate Buchnera gene expression, we further demonstrated the cross-kingdom translocation of aphid argonuate 1 protein (Ago1), into Buchnera using immunolocalization. Given the translocation of both Ago1 and miRNAs, we applied a eukaryotic miRNA target prediction framework and found that all cross-kingdom-translocated miRNAs are predicted to target Buchnera genes involved in symbiotic functions. Although the precise in vivo functions of translocated miRNAs remain challenging to determine, our findings suggest a previously unrecognized layer of regulation between insect host and its obligate endosymbiont, offering new insight into the molecular dialogue that supports insect-microbe interactions, highlighting potential targets for miRNA-based pest management. Significance statementMany insects have evolved bacteriocyte cells to house essential bacterial endosymbionts. However, how bacteriocytes are specified and how gene expression is coordinated between host and symbiont remain largely unknown. Here, we identify that aphid microRNAs, along with an argonaute protein, are translocated into the obligate bacterial endosymbiont Buchnera, revealing a previously unrecognized regulatory layer mediating host and obligate endosymbiont interactions. This discovery provides evidence of miRNA cross-kingdom movement into an obligate endosymbiont, filling a key knowledge gap in how eukaryotic host small RNAs can influence microbial partners. Given the critical role of Buchnera in aphid survival and reproduction, these findings not only advance fundamental knowledge of insect-microbe interactions but also point to new molecular targets for innovative pest management strategies.

evolutionary biology↗

bioRxiv2025

2-Oxoglutarate-dependent dioxygenases contribute to cardenolide biosynthesis in Erysimum cheiranthoides (wormseed wallflower)

O_LICardenolide biosynthesis evolved convergently in several plant lineages, including wallflowers (Erysimum, Brassicaceae). Although the first steps of the biosynthetic pathway, which involve conversion of sterols to pregnane derivatives, have been characterized in Erysimum cheiranthoides and other species, key enzymes that catalyze the 14{beta}- and 21-hydroxylation of the steroid core remained elusive. C_LIO_LIIn this study, we used comparative transcriptomic analysis of different Erysimum species to identify 2-oxoglutarate dependent dioxygenases (2OGDs) that catalyze these reactions in E. cheiranthoides: Erche03g034150 (CARDENOLIDE METABOLISM 5; CARD5), which is related to ALKENYL HYDROXYALKYL PRODUCING 1 (AOP1), and Erche01g020322 (CARDENOLIDE METABOLISM 6; CARD6), which arose from a duplication of DIOXYGENASE FOR AUXIN OXIDATION 1 (DAO1). C_LIO_LIKnockout mutants of both genes are deficient in cardenolide biosynthesis and instead accumulate pathway intermediates. Based on transient expression and activity in Nicotiana benthamiana, and we identified CARD5 as the likely 14{beta}-hydroxylase, and CARD6 as the 21-oxygenase. Finally, enzyme modeling and substrate docking identified key residues that may allow shifts to substrate recognition during neofunctionalization. C_LIO_LIThe results of this research provide new insight into the evolution of cardenolide biosynthesis and have potential practical applications in the engineering of steroid-derived compounds for medical uses. C_LI

plant biology↗

bioRxiv2025

Modification of Non-photochemical Quenching Pathways in the C4 Model Plant Setaria viridis Revealed Shared and Unique Photoprotection Mechanisms as Compared to C3 Plants

Light is essential for photosynthesis; however, excess light can increase the accumulation of photoinhibitory reactive oxygen species that reduce photosynthetic efficiency. Plants have evolved photoprotective non-photochemical quenching (NPQ) pathways to dissipate excess light energy. In tobacco and soybean (C3 plants), overexpression of three NPQ genes, violaxanthin de-epoxidase (VDE), Photosystem II Subunit S (PsbS), and zeaxanthin epoxidase (ZEP), hereafter VPZ, resulted in faster NPQ induction and relaxation kinetics, and increased crop yields in field conditions. NPQ is well-studied in C3 plants; however, NPQ and the translatability of the VPZ approach in C4 plants is poorly understood. The green foxtail Setaria viridis is an excellent model to study photosynthesis and photoprotection in C4 plants. To understand the regulation of NPQ and photosynthesis in C4 plants, we performed transient overexpression in Setaria protoplasts and generated (and employed) stable transgenic Setaria plants overexpressing one of the three Arabidopsis NPQ genes or all three NPQ genes (AtVPZ lines). Overexpressing (OE) AtVDE and AtZEP in Setaria produced similar results as in C3 plants, with increased or reduced zeaxanthin (thus NPQ), respectively. However, overexpressing AtPsbS appeared to be challenging in Setaria, with largely reduced NPQ in protoplasts and under-represented homozygous AtPsbS-OE lines, potentially due to competitive and tight heterodimerization of AtPsbS and SvPsbS proteins. Furthermore, Setaria AtVPZ lines had increased zeaxanthin, faster NPQ induction, higher NPQ level, but slower NPQ relaxation. Despite this, AtVPZ lines had improved growth as compared to wildtype under several conditions, especially high temperatures, which is not related to the faster relaxation of NPQ but may be attributable to increased zeaxanthin and NPQ in C4 plants. Our results identified shared and unique characteristics of the NPQ pathway in C4 model Setaria as compared to C3 plants and provide insights to improve C4 crop yields under fluctuating environmental conditions.

plant biology↗

bioRxiv2024

Overexpression of Xanthophyll Cycle Genes Leads to Faster NPQ Acclimation in the C4 Monocot Setaria viridis

Slow relaxation and induction of Non-Photochemical Quenching (NPQ) limits plant productivity under fluctuating light in C3 plants but it is unknown if this trait extends to C4 plants. Three genes have been implicated in determining NPQ induction and relaxation rates under intermittent leaf shading; VDE and ZEP interconvert the xanthophyll pigments violaxanthin and zeaxanthin, and PsbS regulates the overall level of NPQ. Here we report the overexpression of the Arabidopsis thaliana VDE, ZEP, and PsbS in the NADP-Malic Enzyme C4 monocot Setaria viridis. We demonstrate these transgenic plants have faster NPQ induction and relaxation under fluctuating light but observe no impact on Photosystem II photochemistry yield. Under illumination, faster NPQ induction resulted in higher transient NPQ levels and a lower overall chlorophyll fluorescence yield. Together this introduces the potential for lower productivity due to over-quenching of chlorophyll during light fluctuation. Although we observed faster NPQ acclimation rates in our transgenic lines, hyperspectral imaging and pigment analysis suggest that there is little photosynthetic advantage to increasing NPQ acclimation over wildtype due to naturally fast C4 acclimation rates. These results indicate that further work is necessary in evaluating the role of NPQ acclimation in C4 growth dynamics towards the goal of improving crop productivity.

plant biology↗

bioRxiv2024

Catechol acetylglucose: A newly identified benzoxazinoid-regulated defensive metabolite in maize

An enormous diversity of specialized metabolites is produced in the plant kingdom, with each individual plant synthesizing thousands of these compounds. Previous research showed that benzoxazinoids, the most abundant class of specialized metabolites in maize, also function as signaling molecules by regulating the production callose as a defense response. In this study, we identified catechol acetylglucose (CAG) as a benzoxazinoid-regulated metabolite that is produced from salicylic acid via catechol and catechol-glucoside. Genome wide association studies of CAG abundance identified a gene encoding a predicted acetyltransferase. Knockout of this gene resulted in maize plants that lack CAG and over-accumulate catechol glucoside. Upon tissue disruption, maize plants accumulate catechol, which inhibits Spodoptera frugiperda (fall armyworm) growth. Analysis of caterpillar frass showed that S. frugiperda detoxifies catechol by glycosylation, and the efficiency of catechol glycosylation was correlated with S. frugiperda growth on a catechol-containing diet. Thus, the success of S. frugiperda as an agricultural pest may depend partly on its ability to detoxify catechol, which is produced as a defensive metabolite by maize plants.

plant biology↗

bioRxiv2024

Four enzymes control natural variation in the steroid core of Erysimum cardenolides

Plants commonly produce families of structurally related metabolites with similar defensive functions. This apparent redundancy raises the question of underlying molecular mechanisms and adaptive benefits of such chemical variation. Cardenolides, a class defensive compounds found in the wallflower genus Erysimum (L., Brassicaceae) and scattered across other plant families, show substantial structural variation, with glycosylation and hydroxylation being common modifications of a steroid core, which itself may vary in terms of stereochemistry and saturation. Through a combination of chemical mutagenesis and analysis of gene coexpression networks, we identified four enzymes involved in cardenolide biosynthesis in Erysimum that work together to determine stereochemistry at carbon 5 of the steroid core: Ec3{beta}HSD, a 3{beta}-hydroxysteroid dehydrogenase, Ec3KSI, a ketosteroid isomerase, EcP5{beta}R2, a progesterone 5{beta}-reductase, and EcDET2, a steroid 5-reductase. We biochemically characterized the activity of these enzymes in vitro and generated CRISPR/Cas9 knockout lines to confirm activity in vivo. Cardenolide biosynthesis was not eliminated in any of the knockouts. Instead, mutant plants accumulated cardenolides with altered saturation and stereochemistry of the steroid core. Furthermore, we found variation in carbon 5 configuration among the cardenolides of 44 species of Erysimum, where the occurrence of some 5{beta}-cardenolides is associated with the expression and sequence of P5{beta}R2. This may have allowed Erysimum species to fine-tune their defensive profiles to target specific herbivore populations over the course of evolution. SIGNIFICANCE STATEMENTPlants use an array of toxic compounds to defend themselves from attack against insects and other herbivores. One mechanism through which plants may evolve more toxic compounds is through modifications to the structure of compounds they already produce. In this study, we show how plants in the wallflower genus Erysimum use four enzymes to fine-tune the structure of toxic metabolites called cardenolides. Natural variation in the sequence and expression of a single enzyme called progesterone 5{beta}-reductase 2 partly explains the variation in cardenolides observed across the Erysimum genus. These alterations to cardenolide structure over the course of evolution suggests that there may be context-dependent benefits to Erysimum to invest in one cardenolide variant over another.

plant biology↗

bioRxiv2024

Regulation of Arabidopsis polyamine acetylation by NATA1 and NATA2

Polyamines have vital functions in organisms, including bacteria, plants, and animals, with key roles in growth, development, and stress responses. Spermine/spermidine N1-acetyl transferases (SSATs) regulate polyamine abundance by catalysing their N-acetylation, thereby reducing the pool of polyamines and producing other bioactive components. The regulatory mechanisms controlling SSAT enzymes are incompletely understood. Here, we investigate the biological role and regulation of the two SSAT isoforms present in Arabidopsis thaliana, N-ACETYLTRANSFERASE ACTIVITY (NATA) 1 and 2. We show that NATA2 is a heat-stable isoform, induced in response to heat. Intriguingly, a nata2 knockout mutation proved beneficial for growth and pathogen defence under heat stress in Arabidopsis, aligning with the stress-mitigating effect of polyamines. In contrast, the double knockout of nata1 and nata2 was lethal, highlighting the essential role of basal SSAT activity. Our numerous crystal structures of both NATAs, supported by functional assays, revealed that stress-produced acidic metabolites can selectively inhibit polyamine acetylation by occupying the NATA substrate-binding pocket. This environment-responsive regulation mechanism may allow Arabidopsis to adjust the deleterious action of NATAs under stress conditions, without eliminating the enzyme. More generally, metabolite-ensemble inhibition may be a novel paradigm for non-genetic feedback regulation of plant enzymes.

plant biology↗

bioRxiv2024

Nicotine has a minor role in protecting field-grown Nicotiana benthamiana against insect herbivory

Plants produce an immense diversity of defensive specialized metabolites. However, despite extensive functional characterization, the relative importance of different defensive compounds is rarely examined in natural settings. Here, we compare the efficacy of three Nicotiana benthamiana defensive compounds, nicotine, acylsugars, and a serine protease inhibitor, by growing plants with combinations of knockout mutations in a natural setting, quantifying invertebrate interactions, and comparing relative plant performance. Among the three tested compounds, acylsugars had the greatest defensive capacity, affecting aphids, leafhoppers, spiders, and flies. Nicotine mutants displayed increased leafhopper feeding and aphid colonization. Plants lacking both nicotine and acylsugars were more susceptible to flea beetles and thrips. By contrast, knockout of the serine protease inhibitor did not affect insect herbivory in the field. Complementary experiments under controlled laboratory conditions with caterpillars grasshoppers, and aphids confirmed results obtained in a natural setting. We conclude that the three metabolite groups collectively provide broad-spectrum protection to N. benthamiana. However, there is a gradient in their effects on the interacting invertebrates present in the field. Furthermore, we demonstrate that, even if individual metabolites do not have a measurable defensive benefit on their own, they can have an additive effect when combined with other defensive compounds.

plant biology↗

bioRxiv2024

Aphid resistance segregates independently of cardiac glycoside and glucosinolate content in an Erysimum cheiranthoides (wormseed wallflower) F2 population

Plants in the genus Erysimum produce both glucosinolates and cardiac glycosides as defense against herbivory. Two natural isolates of Erysimum cheiranthoides (wormseed wallflower) differed in their glucosinolate content, cardiac glycoside content, and resistance to Myzus persicae (green peach aphid), a broad generalist herbivore. Both classes of defensive metabolites were produced constitutively and were not induced further by aphid feeding. To investigate the relative importance of glucosinolates and cardiac glycosides in E. cheiranthoides defense, we generated an improved genome assembly, genetic map, and segregating F2 population. Genotypic and phenotypic analysis of the F2 plants identified quantitative trait loci affecting glucosinolates and cardiac glycosides, but not aphid resistance. The abundance of most glucosinolates and cardiac glycosides was positively correlated in the F2 population, indicating that similar processes regulate their biosynthesis and accumulation. Aphid reproduction was positively correlated with glucosinolate content. Although overall cardiac glycoside content had little effect on aphid growth and survival, there was a negative correlation between aphid reproduction and helveticoside abundance. However, this variation in defensive metabolites could not explain the differences in aphid growth on the two parental lines, suggesting that processes other than the abundance of glucosinolates and cardiac glycosides have a predominant effect on aphid resistance in E. cheiranthoides.

plant biology↗

bioRxiv2024

Genome and tissue-specific transcriptome of the tropical milkweed (Asclepias curassavica)

Tropical milkweed (Asclepias curassavica) serves as a host plant for monarch butterflies (Danaus plexippus) and other insect herbivores that can tolerate the abundant cardiac glycosides that are characteristic of this species. Cardiac glycosides, along with additional specialized metabolites, also contribute to the ethnobotanical uses of A. curassavica. To facilitate further research on milkweed metabolism, we assembled the 197 Mbp genome of a fifth-generation inbred line of A. curassavica into 619 contigs, with an N50 of 10 Mbp. Scaffolding resulted in 98% of the assembly being anchored to 11 chromosomes, which are mostly colinear with the previously assembled common milkweed (A. syriaca) genome. Assembly completeness evaluations showed that 98% of the BUSCO gene set is present in the A. curassavica genome assembly. The transcriptomes of six tissue types (young leaves, mature leaves, stems, flowers, buds, and roots), with and without defense elicitation by methyl jasmonate treatment, showed both tissue-specific gene expression and induced expression of genes that may be involved in cardiac glycoside biosynthesis. Expression of a CYP87A gene, the predicted first gene in the cardiac glycoside biosynthesis pathway, was observed only in the stems and roots and was induced by methyl jasmonate. Together, this genome sequence and transcriptome analysis provide important resources for further investigation of the ecological and medicinal uses of A. curassavica.

plant biology↗

bioRxiv2023

Reversing the escape from herbivory: Knockout of cardiac glycoside biosynthesis in wormseed wallflower (Erysimum cheiranthoides L., Brassicaceae)

O_LIThe chemical arms race between plants and insects is foundational to the generation and maintenance of biological diversity. We asked how the evolution of a novel defensive compound in an already well-defended plant lineage impacts interactions with diverse herbivores. Erysimum cheiranthoides (Brassicaceae), which produces both ancestral glucosinolates and novel cardiac glycosides, served as a model. C_LIO_LIWe analyzed gene expression to identify cardiac glycoside biosynthetic enzymes in E. cheiranthoides and characterized these enzymes via heterologous expression and CRISPR/Cas9 knockout. Using E. cheiranthoides cardiac glycoside-deficient lines, we conducted insect experiments in both the laboratory and field. C_LIO_LIEcCYP87A126 initiates cardiac glycoside biosynthesis via sterol side chain cleavage, and EcCYP716A418 has a role in cardiac glycoside hydroxylation. In EcCYP87A126 knockout lines, cardiac glycoside production was eliminated. Laboratory experiments with these lines revealed that cardiac glycosides were highly effective defenses against two species of glucosinolate-tolerant specialist herbivores but did not protect against all crucifer-feeding specialist herbivores in the field. Cardiac glycosides had lesser to no effect on two broad generalist herbivores. C_LIO_LIThese results begin elucidation of the E. cheiranthoides cardiac glycoside biosynthetic pathway and demonstrate in vivo that cardiac glycoside production allows Erysimum to escape from some, but not all, specialist herbivores. C_LI

ecology↗

bioRxiv2023

Serine proteinase inhibitors from Nicotiana benthamiana, a non-preferred host plant, inhibit the growth of Myzus persicae (green peach aphid)

The green peach aphid (Myzus persicae) is a severe agricultural crop pest that has developed resistance to most current control methods, requiring the urgent development of novel strategies. Plant proteinase inhibitors (PINs) are small proteins that protect plants against pathogens and/or herbivores, likely by preventing efficient protein digestion. We identified 67 protease genes in the transcriptomes of three M. persicae lineages (USDA-Red, G002, and G006). Comparison of gene expression levels in aphid guts and whole aphids showed that several proteases, including a highly expressed serine protease, are significantly overexpressed in the guts. Furthermore, we identified three genes encoding serine protease inhibitors (SerPIN-II1, 2, and 3) in Nicotiana benthamiana, which is a non-preferred host for M. persicae. Using virus-induced gene silencing (VIGS) with a tobacco rattle virus (TRV) vector and overexpression with a turnip mosaic virus (TuMV) vector, we demonstrated that N. benthamiana SerPIN-II1 and SerPIN-II2 cause reduced survival and growth, but do not affect aphid protein content. Similarly, SerPIN-II3 overexpression reduced survival and growth, and serpin-II3 knockout mutations, which we generated using CRISPR/Cas9, increased survival and growth. Whereas protein content was significantly increased in aphids fed on SerPIN-II3 overexpressing plants, it was decreased in aphids fed on serpin-II3 mutants. Together, our results show that three PIN-IIs from N. benthamiana, a non-preferred host plant, effectively inhibit M. persicae survival and growth, thereby representing a new resource for the development of aphid-resistant crop plants.

plant biology↗

bioRxiv2023

Maize COI1 quadruple-knockout mutants exhibit elevated DELLA protein accumulation, stunted growth, and reduced photosynthetic efficiency

The F-box protein Coronatine Insensitive (COI) is a receptor for the jasmonic acid signaling pathway in plants. To investigate the functions of the six maize COI proteins (COI1a, COI1b, COI1c, COI1d, COI2a, and COI2b), we made single, double, and quadruple loss-of-function mutants. Double-mutant coi2a coi2b pollen was inviable, and no homozygous mutant plants were obtained. The coi1 quadruple mutant (coi1-4x) exhibited shortened internode lengths, decreased photosynthesis, leaf discoloration, microelement deficiencies, and accumulation of DWARF9, a DELLA-family protein that represses the gibberellic acid signaling pathway. Co-expression of maize COI and DWARF9 genes in Nicotiana benthamiana showed that the COI proteins lead to proteasome-dependent DELLA degradation. Many genes expressed at lower levels in the coi1-4x mutant are normally induced by gibberellic acid. The majority of these genes are predicted to be bundle sheath or mesophyll-enriched including those encoding C4-specific photosynthetic enzymes. Ectopic expression of maize COI genes in N. benthamiana showed that COI2a is fully localized in the nucleus and interacts with maize JAZ proteins, the canonical COI repressor partners. However, maize COI1a and COI1c proteins showed only partial nuclear localization and failed to bind to most of the JAZ proteins tested. These results show divergent functions of the six COI proteins in the regulation of maize growth and defense pathways.

plant biology↗

bioRxiv2022

Horizontally transferred genes as RNA interference targets for aphid and whitefly control

RNA interference (RNAi)-based technologies are starting to be commercialized as a new approach for agricultural pest control. Horizontally transferred genes (HTGs), which have been transferred into insect genomes from viruses, bacteria, fungi, or plants, are attractive targets for RNAi-mediated pest control. HTGs are often unique to a specific insect family or even genus, making it unlikely that RNAi constructs targeting such genes will have negative effects on ladybugs, lacewings, and other beneficial predatory insect species. In this study, we sequenced the genome of a red, tobacco-adapted isolate of Myzus persicae (green peach aphid) and bioinformaticaly identified 30 HTGs. We then used plant-mediated virus-induced gene silencing (VIGS) to show that several HTGs of bacterial and plant origin are important for aphid growth and/or survival. Silencing the expression of fungal HTGs did not affect aphid survivorship, but decreased aphid reproduction. Importantly, although there was uptake of plant-expressed RNA by Coccinella septempunctata (seven-spotted ladybugs) via the aphids that they consumed, we did not observe negative effects on ladybugs from aphid-targeted VIGS constructs. In other experiments, we targeted five Bemisia tabaci (whitefly) HTGs using VIGS and demonstrated that knockdown of some of these genes affected whitefly survival. As functional HTGs have been identified in the genomes of numerous pest species, we propose that these HTGs should be explored further as efficient and safe targets for control of insect pests using plant-mediated RNA interference.

plant biology↗

bioRxiv2022

Use of sugarcane mosaic virus for virus-induced gene silencing in maize

Previously, sugarcane mosaic virus (SCMV) was developed as a vector for transient expression of heterologous genes in Zea mays (maize). Here we show that SCMV can also be applied for virus-induced gene silencing (VIGS) of endogenous maize genes. Comparison of sense and antisense VIGS constructs targeting maize PDS (phytoene desaturase) showed that antisense constructs resulted in a greater reduction in gene expression. In a time course of gene expression after infection with VIGS constructs targeting PDS, Les22 (Lesion mimic 22), and Ij1 (Iodent japonica1), efficient expression silencing was observed two, three, and four weeks after infection with SCMV. However, at week five, expression of Les22 and Ij1 was no longer significantly reduced compared to control plants. The defense signaling molecule jasmonate-isoleucine (JA-Ile) can be inactivated by 12C-hydroxylation and hydrolysis, and knockout of these genes leads to increased herbivore resistance. JA-Ile hydroxylases and hydrolases have been investigated in Arabidopsis, rice, and Nicotiana attenuata. To determine whether the maize homologs of these genes function in plant defense, we silenced expression of ZmCYP94B1 (predicted JA-Ile hydroxylase) and ZmJIH1 (predicted JA-Ile hydrolase) by VIGS with SCMV. Although ZmCYP94B1 and ZmJIH1gene expression silencing increased resistance to Spodoptera frugiperda (fall armyworm), Schistocerca americana (American birdwing grasshopper), and Rhopalosiphum maidis (corn leaf aphid), there was no additive effect from silencing the expression of both genes. Further work will be required to determine the more precise functions of these enzymes in regulating maize defenses.

plant biology↗

bioRxiv2021

Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Plant specialized metabolites are often subject to within-plant transport and have tissue-specific distribution patterns. Among plants in the Brassicaceae, the genus Erysimum is unique in producing not only glucosinolates but also cardenolides as defense against insect herbivory. Ten cardenolides were detected with varying abundance in different tissues of Erysimum cheiranthoides (wormseed wallflower). As is predicted by the optimal defense theory, cardenolides were most abundant in young leaves and reproductive tissues. The lowest concentrations were observed in senescing leaves and roots. Crosses between wildtype E. cheiranthoides and a mutant line with an altered cardenolide profile showed that the seed cardenolide phenotype is determined entirely by the maternal genotype. Prior to the development of the first true leaves, seedling cotyledons also had the maternal cardenolide profile. Hypocotyl grafting experiments showed that the root cardenolide profile is determined entirely by the aboveground plant genotype. In further grafting experiments, there was no evidence of cardenolide transport into the leaves, but a mixed cardenolide profile was observed in the stems and inflorescences of plants that had been grafted at vegetative and flowering growth stages, respectively. Together, these results indicate that E. cheiranthoides leaves are a site of cardenolide biosynthesis and therefore also the plant tissue that is most likely to be expressing the relevant biosynthetic genes.

plant biology↗

bioRxiv2021

Fatty Alcohols, a Minor Component of the Tree Tobacco Surface Wax, Reduce Insect Herbivory

Despite decades of research resulting in a comprehensive understanding of epicuticular wax biosynthesis and metabolism, the function of these almost ubiquitous metabolites in plant-herbivore interactions remains unresolved. To develop a better understanding of this role, we investigated plant-herbivore interactions in four Nicotiana glauca (tree tobacco) genome edited mutants. This included [eceriferum1 (cer1), eceriferum3 (cer3), {beta}-ketoacyl-coA synthase6 (kcs6), and fatty acyl-coA reductase (far)] displaying a wide range of alkane and fatty alcohol abundances. Three interaction classes were examined: chewing herbivory with seven caterpillar and one snail species, phloem feeding with Myzus persicae (green peach aphid), and egg laying with Bemisia tabaci (sweet potato whitefly). We found that high wax load and alkane abundance did not reduce caterpillar or snail herbivory. However, fatty alcohol content was negatively correlated with caterpillar growth, suggesting a role in reducing insect herbivory despite its lower levels. Aphid reproduction and feeding activity were not correlated with wax load and composition but are potentially affected by altered cutin composition of cer1 mutants. When examining non-feeding activities, wax crystal morphology could explain the preference of B. tabaci to lay eggs on wildtype plants relative to cer1 and far mutants. Accordingly, the fatty alcohol wax component reduces caterpillar herbivory on the chemical level, but oviposition is increased when wax crystals are dense. The results suggest that this varied response between herbivore classes and species, at times displaying increased and at times reduced fitness in response to altered wax composition is in part a consequence of co-evolution that shaped the specific effects of different N. glauca metabolites such as anabasine and fatty alcohols in plant-herbivore interactions.

plant biology↗