Biology subjects

van der Hoorn, R.

Publications and source records attributed to van der Hoorn, R..

5 recordsLinked to original sources

bioRxiv2026

A membrane-anchored inhibitor of papain-like cysteine proteases promotes Pseudomonas root colonization

Pseudomonas species, spanning both beneficial and pathogenic lifestyles, possess conserved mechanisms to modulate plant immunity. Nevertheless, the mechanisms by which commensal bacteria establish and maintain host colonization remain poorly understood. Here, we report the characterization of a Pseudomonas chagasin-like protease inhibitor (Cpi1), conserved across pseudomonads representing a novel class of membrane-anchored PLCP inhibitor. Unlike previously described secreted protease inhibitors, P. putida Cpi1 is a lipoprotein localized to the bacterial surface and outer membrane vesicles (OMVs), positioning it to selectively inhibit immune-related papain-like cysteine proteases (PLCPs) during host interactions. Functional assays demonstrated inhibition of maize PLCP activity in the nanomolar range, while cpi1 deletion and chagasin motif mutants exhibited significantly impaired early root colonization, particularly in the meristematic and elongation zones. Besides, lack of cpi1 resulted in an altered structure of a maize root-associated synthetic community. We hypothesize that, Cpi1 may protect critical bacterial surface proteins from cleavage by inhibiting plant proteases and thereby modulate the release of MAMPs, dampening host immune responses. Moreover, the release of Cpi1 via OMVs could further extend its function within the root periphery and the apoplast. Together, our results uncover a conserved, membrane-anchored mechanism among pseudomonads for subverting plant immunity and establishing host-microbe interactions.

microbiology↗

bioRxiv2025

A secreted citrus protease cleaves an outer membrane protein of the Huanglongbing pathogen

Plants secrete a variety of proteases as a defense response during infection by microbial pathogens. However, the relationship between their catalytic activities and antimicrobial functions remains largely unknown. Particularly, few biologically relevant substrates of these proteases have been identified. Huanglongbing (HLB) has been a major threat to the citrus industry worldwide. The HLB-associated bacterium, Candidatus Liberibacter asiaticus (Las), was previously shown to deploy an inhibitor of papain-like cysteine proteases (PLCPs) to promote disease in citrus. In this study, we identified an outer membrane protein (OMP) of Las, LasOMP1, as a substrate of the citrus PLCP CsRD21a. LasOMP1 is one of the most highly expressed genes in Las. CsRD21a cleaves LasOMP1 and produces cleaved peptide products, which could be detected in vitro and in HLB-diseased citrus plants. We found that CsRD21a targets the N-terminal portion of LasOMP1, potentially at an extracellular loop region. Importantly, transgenic sweet orange overexpressing CsRD21a showed reduced Las titers and delayed disease symptoms, highlighting that engineering this protease is a promising strategy to enhance HLB resistance in citrus. Together, our work reveals a pathogen-derived substrate of plant PLCPs and highlights bacterial OMPs as direct targets of plant defense. Significance StatementHuanglongbing (HLB) is the most devastating disease of citrus with no resistance having been identified in commercial cultivars. Previous work implicated papain-like cysteine proteases (PLCPs) as an important hub of defense in citrus; however, their precise role in HLB tolerance remained unclear. Here, we identify and characterize an outer membrane protein (OMP) from the HLB-associated bacterium as a substrate of the citrus PLCP RD21a. We demonstrate a specific cleavage of the bacterial OMP by citrus RD21a, which may impair pathogen growth and/or activate plant immunity. Importantly, overexpression of RD21a enhances HLB tolerance in sweet oranges. This work identifies OMPs as substrates of plant PLCPs and provides insights into protease defense functions.

plant biology↗

bioRxiv2024

SBT5.2s are the major active extracellular subtilases processing IgG antibody 2F5 in the Nicotiana benthamiana apoplast

Plants offer a powerful platform for recombinant protein production but degradation of recombinant proteins by endogenous proteases is causing severe yield losses. Here, we introduce triple knockout lines for SBT5.2, the major active subtilases in the apoplast of agroinfiltrated Nicotiana benthamiana. HIV-neutralising IgG antibody 2F5 is no longer cleaved in the apoplast of sbt5.2 mutants and these mutants accumulate 3-fold more 2F5 upon transient expression but grow normally. Remarkably, however, 2F5 does not accumulate in the apoplast and is not exposed to SBT5.2 when transiently expressed, uncovering an important controversy regarding the subcellular localisation of IgGs in agroinfiltrated plants.

plant biology↗

bioRxiv2023

Cautionary note on ribonuclease activity of recombinant PR-10 proteins

We studied the biochemical properties of three splicing isoforms of PR-10 from rubber tree (Hevea brasiliensis) and found that purified recombinant HbPR10 can cause RNA degradation in vitro, a well-known activity described for many PR-10 proteins. This ribonuclease activity was observed for all three HbPR10 splicing isoforms and is abolished by boiling. However, inclusion of a negative control proteins revealed that ribonuclease activity rather originates from RNases that are copurified from E. coli, which are overlooked by traditionally used controls such as heat inactivation, RNase inhibitors and negative control proteins obtained with different procedures. The crucial control proteins are missing for at least nine reports on ribonuclease activity in PR-10 proteins published by different laboratories worldwide, indicating that proper controls are frequently overlooked in ribonuclease assays. The raised cautionary note applies to several PR-10 proteins with proclaimed ribonuclease activities and call for the use of different assays and mutant PR-10 proteins as control.

plant biology↗

bioRxiv2020

Proteome-wide Profiling of RNA-Binding Protein Responses to flg22 Reveals Novel Components of Plant Immunity

RNA-binding proteins (RBPs) play critical roles in post-transcriptional gene regulation and are known to contribute to plant immunity. To understand the responses of cellular RBPs to an immune elicitor, we applied RNA interactome capture to Arabidopsis leaves treated with flg22. Strikingly, flg22 induced a pervasive remodelling of the cellular RBPome affecting 186 proteins. Flg22-responsive RBPs included classical RBPs involved in RNA metabolism as well as non-canonical RBPs. RBP responders detected after 2h of treatment are enriched in putative sites for post-translational modifications, which may play a regulatory role. By contrast, changes in RBP abundance becomes increasingly important for the RBPome responses to flg22 after 12h. Plant resistance to Pseudomonas syringae is strongly altered in mutant lines lacking individual flg22-responsive RBPs, supporting the importance of RBP dynamics in plant immunity. This study provides a comprehensive and systematic census of flg22 responsive plant RBPs, discovering novel components of plant immunity.

molecular biology↗