Biology subjects

Raffeiner, M.

Publications and source records attributed to Raffeiner, M..

5 recordsLinked to original sources

bioRxiv2024

Cross-species interactome analysis uncovers a conserved selective autophagy mechanism for protein quality control in plants

Selective autophagy is a fundamental protein quality control pathway that safeguards proteostasis by degrading damaged or surplus cellular components, particularly under stress. This process is orchestrated by selective autophagy receptors (SARs) that direct specific cargo for degradation. While significant strides have been made in understanding the molecular framework of selective autophagy, the diversity of SAR repertoires across species remain largely unexplored. Through a comparative interactome analysis across five model organisms, we identified a suite of conserved and lineage-specific SAR candidates. Among these, we validated CESAR as a conserved SAR critical for proteostasis under heat stress. CESAR specifically facilitates the degradation of hydrophobic, ubiquitinated protein aggregates and is indispensable for heat stress tolerance. Our study offers a rich resource for SAR discovery and positions CESAR as a pivotal regulator of proteostasis, with broad implications for improving stress resilience in plants.

plant biology↗

bioRxiv2024

XopM, a FFAT motif containing type-III effector protein from Xanthomonas, suppresses PTI responses at the plant plasma membrane

Many Gram-negative pathogenic bacteria use type-III effector proteins (T3Es) as essential virulence factors to suppress host immunity and to cause disease. However, in many cases the molecular function of T3Es remains unknown. The plant pathogen Xanthomonas campestris pv. vesicatoria (Xcv) is the causal agent of bacterial spot disease on tomato and pepper plants and is known to translocate around 30 T3Es into its host cell, which collectively suppress plant defense and promote infection. XopM is an Xcv core T3E with unknown function that has no similarity to any other known protein. We found that XopM interacts with vesicle-associated membrane protein (VAMP)-associated proteins (VAPs) in an isoform specific manner. The endoplasmic reticulum (ER) integral membrane protein VAP is a common component of membrane contact sites involved in both tethering and lipid transfer by binding directly to proteins containing a FFAT [two phenylalanines (FF) in an acidic tract (AT)] motif. Sequence analyses revealed that XopM displays two FFAT motifs that cooperatively mediated the interaction of XopM with VAP. When expressed in plants, XopM supports growth of a non-pathogenic bacterial strain and dampens the production of reactive oxygen species, indicating its ability to suppress plant immunity. Further analyses revealed that the interaction with VAP and the ability to suppress PTI are structurally and functionally separable. Although XopM requires localization to the host membrane system for full PTI suppression activity. We discuss a working model in which XopM uses FFAT-motifs to target the membrane in order to interfere with early PTI responses.

plant biology↗

bioRxiv2023

ER-anchored protein sorting controls the fate of two proteasome activators for intracellular organelle communication during proteotoxic stress

Proteotoxic stress, characterized by the accumulation of damaged proteins, poses a significant challenge to cellular homeostasis. To mitigate proteotoxicity eukaryotes employ the proteasome that is regulated by proteasome activators, e.g. transcription factors that promote gene expression of proteasome subunits. As proteotoxicity originates in different compartments, cells need to perceive signals from various locations. Understanding which components integrate signals to address proteotoxicity is essential to develop strategies to cope with proteotoxicity but remain elusive. Here, we identify that the proteasome autoregulatory feedback loop acts as a gatekeeper to facilitate the communication between nucleus and chloroplast. We reveal that the ER-anchored protein sorting system (ERAPS) controls the proteasomal degradation or nuclear translocation of proteasome activators NAC53 and NAC78. While both transcription factors activate the proteasome gene expression, they repress photosynthesis-associated nuclear genes during proteotoxicity through association with a conserved cis-element. Our data implicate a general trade-off between proteasome function and energy metabolism unravelling an unprecedented mechanism of how eukaryotic cells cope with proteotoxicity. Collectively, our discoveries provide a novel conceptual framework in which the proteasome autoregulatory feedback loop coordinates subcellular proteostasis and the trade-off between growth and defence.

plant biology↗

bioRxiv2021

The Xanthomonas type-III effector protein XopS stabilizes CaWRKY40a to regulate defense hormone responses and preinvasion immunity in pepper (Capsicum annuum)

A critical component of plant immunity against invading pathogens is the rapid transcriptional reprogramming of the attacked cell to minimize virulence. Many adapted plant bacterial pathogens use type III effector (T3E) proteins to interfere with plant defense responses, including the induction of immunity genes. The elucidation of effector function is essential to understanding bacterial pathogenesis. Here, we show that XopS, a T3E of Xanthomonas campestris pv. vesicatoria (Xcv), interacts with and inhibits the proteasomal degradation of the transcriptional regulator of defense gene expression WRKY40. Virus-induced gene silencing of WRKY40 in pepper enhanced plant tolerance towards Xcv infection, indicating it represses immunity. Stabilization of WRKY40 by XopS reduces the expression of its targets including salicylic acid (SA)-responsive genes and the jasmonic acid (JA) signaling repressor JAZ8. Xcv bacteria lacking XopS display significantly reduced virulence when surface inoculated onto susceptible pepper leaves. XopS delivery by Xcv, as well as ectopic expression of XopS in Arabidopsis or Nicotiana benthamiana prevented stomatal closure in response to bacteria and biotic elicitors in a WRKY40 dependent manner. This suggests that XopS interferes with preinvasion as well as with apoplastic defense by manipulating WRKY40 stability and gene expression eventually altering phytohormone crosstalk to promote pathogen proliferation.

plant biology↗

bioRxiv2021

Self-ubiquitination of a pathogen type-III effector traps and blocks the autophagy machinery to promote disease

Beyond its role in cellular homeostasis, autophagy plays anti- and pro-microbial roles in host-microbe interactions, both in animals and plants. One prominent role of anti-microbial autophagy is to degrade intracellular pathogens or microbial molecules, in a process termed xenophagy. Consequently, microbes evolved mechanisms to hijack or modulate autophagy to escape elimination. Although well-described in animals, the extent to which xenophagy contributes to plant-bacteria interactions remains unknown. Here, we provide evidence that Xanthomonas campestris pv. vesicatoria (Xcv) suppresses host autophagy by utilizing type-III effector XopL. XopL interacts with and degrades the autophagy component SH3P2 via its E3 ligase activity to promote infection. Intriguingly, XopL is targeted for degradation by defense-related selective autophagy mediated by NBR1/Joka2, revealing a complex antagonistic interplay between XopL and the host autophagy machinery. Our results implicate plant antimicrobial autophagy in depletion of a bacterial virulence factor and unravels an unprecedented pathogen strategy to counteract defense-related autophagy.

plant biology↗