Biology subjects

Stevens, D. M.

Publications and source records attributed to Stevens, D. M..

5 recordsLinked to original sources

bioRxiv2023

Evolutionary dynamics of proteinaceous MAMPs reveals intrabacterial antagonism of plant immune perception

Plants and animals detect biomolecules termed Microbe-Associated Molecular Patterns (MAMPs) and induce immunity. Agricultural production is severely impacted by pathogens which can be controlled by transferring immune receptors. However, most studies use a single MAMP epitope and the impact of diverse multi-copy MAMPs on immune induction is unknown. Here we characterized the epitope landscape from five proteinaceous MAMPs across 4,228 plant-associated bacterial genomes. Despite the diversity sampled, natural variation was constrained and experimentally testable. Immune perception in both Arabidopsis and tomato depended on both epitope sequence and copy number variation. For example, Elongation Factor Tu is predominantly single copy and 92% of its epitopes are immunogenic. Conversely, 99.9% of bacterial genomes contain multiple Cold Shock Proteins and 46% carry a non-immunogenic form. We uncovered a new mechanism for immune evasion, intrabacterial antagonism, where a non-immunogenic Cold Shock Protein blocks perception of immunogenic forms encoded in the same genome. These data will lay the foundation for immune receptor deployment and engineering based on natural variation. Significance StatementPlants recognize pathogens as non-self using innate immune receptors. Receptors on the cell surface can recognize amino acid epitopes present in pathogen proteins. Despite many papers investigating receptor signaling, the vast majority use a single epitope. Here, we analyzed the natural variation across five different epitopes and experimentally characterized their perception in plants. We highlight the importance of analyzing all epitope copies within a pathogen genome. Through genetic and biochemical analyses, we revealed a mechanism for immune evasion, intrabacterial antagonism, where a non-immunogenic epitope blocks perception of immunogenic forms encoded in a single genome. These data can directly inform disease control strategies by enabling prediction of receptor utility and deployment for current and emerging pathogens.

microbiology↗

bioRxiv2022

Overlapping local and systemic defense induced by an oomycete fatty acid MAMP and brown seaweed extract in tomato

Eicosapolyenoic fatty acids are integral components of oomycete pathogens that can act as microbe-associated molecular patterns (MAMPs) to induce disease resistance in plants. Defense inducing eicosapolyenoic fatty acids include arachidonic (AA) and eicosapentaenoic acids, and are strong elicitors in solanaceous plants with bioactivity in other plant families. Similarly, extracts of the brown seaweed, Ascophyllum nodosum, used in sustainable agriculture as a biostimulant of plant growth, may also induce disease resistance. A. nodosum, similar to other macroalgae, is rich in eicosapolyenoic fatty acids, which comprise as much as 25% of total fatty acid composition. We investigated the response of roots and leaves from AA or a commercial A. nodosum extract (ANE) on root-treated tomatoes via RNA sequencing, phytohormone profiling, and disease assays. AA and ANE significantly altered transcriptional profiles relative to control plants, inducing numerous defense-related genes with both substantial overlap as well as differences in gene expression patterns. Root treatment with AA and, to a lesser extent, ANE also altered both salicylic acid and jasmonic acid levels while inducing local and systemic resistance to oomycete and bacterial pathogen challenge. Thus, our study highlights overlap in both local and systemic defense induced by AA and ANE, with potential for inducing broad-spectrum resistance against pathogens.

plant biology↗

bioRxiv2022

Citrus relatives exhibit natural variation in perception and response magnitude to microbial features

Although much is known about the responses of model plants to microbial features, we still lack an understanding of the extent of variation in immune perception across members of a plant family. In this work, we analyzed immune responses in Citrus and wild relatives, surveying 86 Rutaceae genotypes with differing leaf morphologies and disease resistances. We found that responses to microbial features vary both within and between members. Species in two subtribes, the Balsamocitrinae and Clauseninae, can recognize all tested microbial features (flg22, csp22, chitin), including one from Candidatus Liberibacter species (csp22CLas), the bacterium associated with citrus greening disease aka Huanglongbing. We investigated differences at the receptor level for flagellin perception (FLS2 receptor) and chitin perception (LYK5 receptor) in citrus genotypes. We were able to characterize two genetically linked FLS2 homologs from Frost Lisbon lemon (responsive) and Washington navel orange (non-responsive). Surprisingly, FLS2 homologs from responding and non-responding genotypes were expressed in citrus and functional when transferred to a heterologous system. Washington navel orange weakly responds to chitin, but Tango mandarin exhibits a robust response. LYK5 alleles were identical or nearly-identical between the two genotypes and able to complement the Arabidopsis lyk4/lyk5-2 mutant with respect to chitin perception. Collectively, our data indicates that differences in chitin and flg22 perception in these citrus genotypes are not the result of sequence polymorphisms at the receptor level. These findings shed light onto the diversity of perception of microbial features and highlight genotypes capable of recognizing polymorphic pathogen features.

plant biology↗

bioRxiv2020

Citrus vascular proteomics highlights the role of peroxidases and serine proteases during Huanglongbing disease progression

Huanglongbing (HLB) is the most devastating and widespread citrus disease. All commercial citrus varieties are susceptible to the HLB-associated bacterium, Candidatus Liberibacter asiaticus (CLas), which resides in the phloem. The phloem is part of the plant vascular system and is involved in sugar transport. To investigate the plant response to CLas, we enriched for proteins surrounding the phloem in an HLB susceptible sweet orange variety, Washington navel (Citrus sinensis (L) Osbeck). Quantitative proteomics revealed global changes in the citrus proteome after CLas inoculation. Plant metabolism and translation were suppressed, while defense-related proteins such as peroxidases, proteases and protease inhibitors were induced in the vasculature. Transcript accumulation and enzymatic activity of plant peroxidases in CLas infected sweet orange varieties under greenhouse and field conditions were assessed. While peroxidase transcript accumulation was induced in CLas infected sweet orange varieties, peroxidase enzymatic activity varied. Specific serine proteases were upregulated in Washington navel in the presence of CLas based on quantitative proteomics. Subsequent activity-based protein profiling revealed increased activity of two serine proteases, and reduced activity of one protease in two C. sinensis sweet orange varieties under greenhouse and field conditions. The observations in the current study highlight global reprogramming of the citrus vascular proteome and differential regulation of enzyme classes in response to CLas infection. These results open an avenue for further investigation of diverse responses to HLB across different environmental conditions and citrus genotypes.

plant biology↗

bioRxiv2020

Identification of a plant kinase that phosphorylates the bacterial effector AvrPtoB

A critical component controlling bacterial virulence is the delivery of pathogen effectors into plant cells during infection. Effectors alter host metabolism and immunity for pathogen benefit. Multiple effectors are phosphorylated by host kinases, and this posttranslational modification is important for their activity. We sought to identify host kinases involved in effector phosphorylation. Multiple phosphorylated effector residues matched the proposed consensus motif for the plant calcium-dependent protein kinase (CDPK) and Snf1-related kinase (SnRK) superfamily. The conserved Pseudomonas effector AvrPtoB acts as an E3 ubiquitin ligase and promotes bacterial virulence. We identified a member of the Arabidopsis SnRK family, SnRK2.8, which associated with AvrPtoB in yeast and in planta. SnRK2.8 was required for AvrPtoB virulence functions, including facilitating bacterial colonization, suppression of callose deposition, and targeting the plant defense regulator NPR1 and flagellin receptor FLS2. Mass spectrometry revealed AvrPtoB phosphorylation at multiple serine residues in planta, with S258 phosphorylation significantly reduced in the snrk2.8 knockout. AvrPtoB phospho-null mutants exhibited compromised virulence functions and were unable to suppress NPR1 accumulation, FLS2 accumulation, or inhibit FLS2-BAK1 complex formation upon flagellin perception. These data identify a conserved plant kinase utilized by a pathogen effector to promote disease.

plant biology↗