Biology subjects

Steinbrenner, A. D.

Publications and source records attributed to Steinbrenner, A. D..

7 recordsLinked to original sources

bioRxiv2025

Natural variation in expression of a plant immune receptor mediates elicitor sensitivity

Plant immune systems rely on pattern recognition receptors (PRRs) to specifically detect diverse pathogen/pest-associated molecular patterns (PAMPs). While many distinct receptors are known to mediate PAMP recognition, the role of transcriptional regulation of PRRs remains poorly understood. In legume plants, Inceptin Receptor (INR) senses an 11-amino acid peptide, In11, to activate direct and indirect defenses against caterpillar pests. Here we investigated the genetic basis of the rare In11 insensitivity phenotype found in common bean (Phaseolus vulgaris) landraces. Natural variation in the rapid In11-induced ethylene response corresponded with genetic variation at the locus encoding INR itself. Surprisingly, phenotypic variation corresponded with expression level of the INR receptor, rather than coding sequence variation. Promoter sequence variation across 21 accessions of Andean Phaseolus vulgaris, as well as near-isogenic lines (NILs) derived from crosses between an In11-sensitive and insensitive line, corresponded with strength of In11-induced ethylene response. Promoter alleles also corresponded with strength of activation of a luciferase reporter in the heterologous expression model, Nicotiana benthamiana, indicating that cis-element variation is sufficient to drive differences in leaf expression levels. Surprisingly, NILs encoding either WT or the lower expression inr-2 allele did not show differences in resistance to herbivory by beet armyworm (Spodoptera exigua), or in In11-pretreatment protection assays, suggesting that even low INR expression can still mediate effective responses against herbivores despite insensitivity to the In11 elicitor in laboratory assays. Our results demonstrate that natural variation in PRR expression can contribute to differential PAMP responses while not necessarily affecting downstream resistance phenotypes.

plant biology↗

bioRxiv2025

A plant immune receptor mediates tritrophic interactions by linking caterpillar detection to predator recruitment

Plants deploy direct and indirect defenses in response to insect herbivory. The specific antiherbivore responses involve cell surface immune receptors that recognize herbivore associated molecular patterns (HAMPs), yet the ecological relevance of this molecular interplay remains unexplored. We demonstrate that the Inceptin Receptor (INR) encoded by common bean, upon recognition of inceptin, a HAMP in caterpillar oral secretions, orchestrates a tritrophic interaction. Laboratory and field experimentation in Mexico using a naturally occurring inceptin-insensitive mutant and its near-isogenic wild type equivalent, revealed that inceptin recognition by INR activates an herbivore-specific immune pathway, and triggers the emission of a volatile blend that recruits predatory wasps. These findings provide a novel molecular-to-ecological link, revealing how an immune receptor mediates ecologically relevant plant-insect-predator interactions in nature.

plant biology↗

bioRxiv2024

The circadian clock regulates receptor-mediated immune responses to an herbivore-associated molecular pattern

Plants activate induced defenses through the recognition of molecular patterns. Like pathogen-associated molecular patterns (PAMPs), herbivore-associated molecular patterns (HAMPs) can be recognized by cell surface pattern recognition receptors leading to defensive transcriptional changes in host plants. Herbivore-induced defensive outputs are regulated by the circadian clock, but the underlying molecular mechanisms remain unknown. To investigate how the plant circadian clock regulates transcriptional reprogramming of a specific HAMP-induced pathway, we characterized the daytime and nighttime transcriptional response to caterpillar-derived In11 peptide, in the legume crop cowpea (Vigna unguiculata). Using diurnal and free-running conditions, we found that daytime In11 elicitation resulted in stronger late-induced gene expression than nighttime. Plants with a conditional arrhythmic phenotype in constant light (LL) conditions lost time-of-day dependent responses to In11 treatment, and this was associated with arrhythmic expression of circadian clock core transcription factor Late Elongated Hypocotyl VuLHY1 and VuLHY2. Reporter assays with VuLHY homologs indicated that they interact with the promoter of daytime In11-induced Kunitz Trypsin Inhibitor (VuKTI) via a canonical and a polymorphic CCA1/LHY Binding Site (CBS), consistent with a mechanism of direct regulation by circadian clock transcription factors. This study improves our understanding of the time-dependent mechanisms that regulate herbivore-induced gene expression.

plant biology↗

bioRxiv2022

Bringing Plant Immunity to Light: A Genetically Encoded, Bioluminescent Reporter of Pattern Triggered Immunity in Nicotiana benthamiana

Plants rely on innate immune systems to defend against a wide variety of biotic attackers. Key components of innate immunity include cell-surface pattern recognition receptors (PRRs), which recognize pest/pathogen-associated molecular patterns (PAMPs). Unlike other classes of receptors which often have visible cell death immune outputs upon activation, PRRs generally lack rapid methods for assessing function. Here, we describe a genetically encoded bioluminescent reporter of immune activation by heterologously-expressed PRRs in the model organism Nicotiana benthamiana. We characterized N. benthamiana transcriptome changes in response to Agrobacterium tumefaciens (Agrobacterium) and subsequent PAMP treatment to identify PTI-associated marker genes, which were then used to generate promoter-luciferase fusion fungal bioluminescence pathway (FBP) constructs. A reporter construct termed pFBP_2xNbLYS1::LUZ allows for robust detection of PTI activation by heterologously expressed PRRs. Consistent with known PTI signaling pathways, activation by receptor-like protein (RLP) PRRs is dependent on the known adaptor of RLP PRRs, SOBIR1. This system minimizes the amount of labor, reagents, and time needed to assay function of PRRs and displays robust sensitivity at biologically relevant PAMP concentrations, making it ideal for high throughput screens. The tools described in this paper will be powerful for studying PRR function and investigations to characterize the structure-function of plant cell surface receptors.

plant biology↗

bioRxiv2022

Evolutionary gain and loss of a plant pattern-recognition receptor for HAMP recognition

Pattern recognition receptors (PRR) recognize distinct pathogen and herbivore-associated molecular patterns (PAMPs and HAMPs) and mediate activation of immune responses, but the evolution of new PRR sensing functions is not well understood. We employed comparative genomics and functional analysis to define evolutionary events leading to the sensing of the peptide HAMP inceptin (In11) by the PRR Inceptin Receptor (INR). Existing and de novo genome assemblies revealed that the presence of a functional INR gene corresponded with In11 response across 55 million years (my) of legume evolution, and that In11 recognition is unique to the clade of Phaseoloid legumes. The INR loci of certain Phaseoloid and non-Phaseoloid species also contain diverse INR-like homologues, suggesting that the evolution of INR receptor function [~]28 mya occurred after an ancestral gene insertion [~]32 mya. Functional analysis of chimeric and ancestrally reconstructed receptors revealed that specific AA differences in the C1 leucine-rich repeat (LRR) domain and C2 intervening motif likely mediated gain of In11 recognition. In summary, we present a conceptual model for the evolution of a defined PRR function based on patterns of INR variation in legumes.

plant biology↗

bioRxiv2021

Signatures of plant defense response specificity mediated by herbivore-associated molecular patterns in legumes

I.Chewing herbivores activate plant defense responses through a combination of mechanical wounding and elicitation by herbivore associated molecular patterns (HAMPs). HAMPs are wound response amplifiers; however, specific defense outputs may also exist that strictly require HAMP-mediated defense signaling. To investigate HAMP-mediated signaling and defense responses, we characterized cowpea transcriptome changes following elicitation by inceptin, a peptide HAMP common in Lepidoptera larvae oral secretions. Following inceptin treatment, we observed large-scale reprogramming of the transcriptome consistent with 3 different response categories: 1) amplification of mechanical wound responses, 2) temporal extension through accelerated or prolonged responses, and 3) examples of inceptin-specific elicitation and suppression. At both early and late timepoints, namely 1 and 6 hours, large sets of transcripts specifically accumulated following inceptin elicitation but not wounding alone. Further inceptin-regulated transcripts were classified as reversing changes induced by wounding alone. Within key signaling and defense related gene families, inceptin-elicited responses commonly targeted select subsets of wound-induced transcripts. Transcripts displaying the largest inceptin-elicited fold-changes included terpene synthases (TPS) and peroxidases (POX) that correspond with induced volatile production and increased peroxidase activity in cowpea. Characterization of inceptin-elicited cowpea defenses via heterologous expression in Nicotiana benthamiana demonstrated that specific cowpea TPS and POX were able to confer terpene emission and the reduced growth of beet armyworm (Spodoptera exigua) herbivores, respectively. Collectively, our present findings in cowpea support a model where HAMP-elicitation both amplifies concurrent wound responses and specifically contributes to the activation of selective outputs associated with direct and indirect anti-herbivore defenses. II. Significance StatementPlants recognize herbivore-associated molecular patterns (HAMPs) to induce defenses, but interactions with the more general wound response are not well-understood. We leveraged a known HAMP-receptor interaction to characterize transcriptomic modulation of the wound response by the peptide HAMP, inceptin. Inceptin not only amplifies wound responses, but can specifically induce or suppress transcripts with demonstrated functions in direct and indirect defense against herbivores. The plant immune system thus recognizes HAMPs to fine-tune wound responses against herbivory.

plant biology↗

bioRxiv2019

A receptor for herbivore-associated molecular patterns mediates plant immunity

Plant-herbivore interactions are ubiquitous across nature and drive major agricultural losses. Inducible defense responses triggered through immune recognition aid in host plant protection; however, specific ligand-receptor pairs mediating the initial perception of herbivory remain unknown. Plants in the subtribe Phaseolinae detect herbivore-associated peptides in caterpillar oral secretions and the defined ligands are proteolytic fragments of chloroplastic ATP synthase termed inceptins. Using forward genetic mapping of inceptin-induced responses, we identify a cowpea (Vigna unguiculata) leucine-rich repeat receptor-like protein as an inceptin receptor (INR) sufficient for elicitor-induced responses and enhanced defense against armyworms (Spodoptera exigua). INR defines a receptor by which plants perceive herbivore-associated molecular patterns (HAMPs) and expands the paradigm of surface immune recognition to attack with mandibles.\n\nOne Sentence SummaryA plant cell surface receptor directly perceives peptides associated with caterpillar herbivory.

plant biology↗