Biology subjects

Djamei, A.

Publications and source records attributed to Djamei, A..

11 recordsLinked to original sources

bioRxiv2026

A fungal effector hijacks conserved plant GSK3-like kinases to reprogram host cell identity

Stable developmental programs normally resist reprogramming, yet pathogens can override these constraints to induce profound tissue and cellular remodeling. How microbial pathogens access conserved developmental signaling networks to reprogram host growth and differentiation remains poorly understood. Here, we show that the maize smut fungus Ustilago maydis deploys the effector Iag1 to reprogram host cell fate by targeting the conserved GSK3-like kinase BIN2. Iag1 contains a PPNT short interaction motif found also in plant viral effectors that mediates its association with BIN2 and related maize GSK3-like kinases and is essential for effector activity and full fungal virulence. This interaction attenuates BIN2-dependent signaling, reduces phosphorylation of the BIN2 substrate BES1, and triggers extensive transcriptional reprogramming consistent with coordinated perturbation of brassinosteroid, auxin, and other BIN2-regulated developmental pathways. These changes result in extensive epidermal developmental reprogramming, including loss of stomatal identity, altered cell division orientation, and aberrant cell expansion. Together, our findings identify GSK3-like kinases as conserved developmental signaling hubs that pathogens can exploit to unlock host developmental plasticity and suggest that short motifs provide an evolutionarily flexible strategy for targeting these central regulatory nodes.

plant biology↗

bioRxiv2025

Pathogenic fungus exploits the lateral root regulators to induce pluripotency in maize shoots

Biotrophic plant pathogens secrete effector molecules to redirect and exploit endogenous signaling and developmental pathways in their favor. The biotrophic fungus Ustilago maydis causes galls on all aerial parts of maize. However, identification and characterization of the responsible gall-inducing effectors and corresponding plant signaling pathway(s) are largely elusive. Here we reveal molecular components acting downstream of a group of plant TOPLESS (TPL)- corepressor interacting fungal effectors that are directly involved in gall formation. We classify these effectors into two classes based on distinct phenotypic responses when individually expressed in planta. While class I responses are characterized by leaf chlorosis, transgenic plants expressing class II TPL-interacting protein (Tip) effectors show a derepression of the AtARF7/AtARF19 branch of auxin signaling, resulting in pluripotent calli formation without the external addition of phytohormones. Subsequent comparative transcriptomics in maize also demonstrates a highly significant overlap of genes up-regulated during U. maydis-triggered leaf gall formation and during the developmental initiation of lateral root formation. This suggests that U. maydis can hijack the lateral root initiation pathway to induce galls in maize shoots. We demonstrate that underlying this is the transcriptional upregulation of downstream LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors. Maize mutants in two LBD genes (ra2, rtcs) led to significantly reduced gall formation following U. maydis infection on homozygous mutants. This study reveals a set of dominantly acting cell proliferation-inducing fungal effectors and provides novel insight into plant developmental pathways that can be hijacked by biotrophic pathogens to induce gall formation.

plant biology↗

bioRxiv2023

Tip of the iceberg? Three novel TOPLESS interacting effectors of the gall-inducing fungus Ustilago maydis

O_LIUstilago maydis is a biotrophic pathogen causing smut disease in maize. It secretes a cocktail of effector proteins during its biotrophic stages in the host plant, which target different host proteins. One such class of proteins we identified previously is TOPLESS (TPL) and TOPLESS RELATED (TPR) transcriptional corepressors. C_LIO_LIHere we screen 297 U. maydis effector candidates for their ability to interact with maize TPL protein RAMOSA 1 ENHANCER LOCUS 2 Like 2 (RELK2) and their ability to induce auxin signaling and thereby identified three novel TPL /TPR interacting effector proteins (Tip6, Tip7 and Tip8). Two of them, Tip6 and Tip7 contain a classical ethylene-responsive element binding factor-associated amphiphilic repression (EAR) motif and interact with maize TPL protein RELK2 in nuclear compartments, whereas Tip8 lacks known TPL interaction motifs and its overexpression in non-host plant leads to cell death indicating recognition of the effector. C_LIO_LIBy using structural modeling, we show an interaction of Tip6 and Tip7 with the previously crystallized EAR motif binding domain of RELK2. Furthermore, by infection assays with an octuple deletion mutant of U. maydis, we demonstrate a role of Tips in U. maydis virulence. Our findings suggest the TOPLESS class of corepressors as a major hub of U. maydis effector proteins. C_LI

plant biology↗

bioRxiv2023

The fungal pathogen Ustilago maydis targets the maize corepressor TPL2 to modulate host transcription for tumorigenesis

Ustilago maydis is a biotrophic fungus that causes tumor formation on all aerial parts of maize. U. maydis secretes effector proteins during penetration and colonization to successfully overcome the plant immune response and reprogram host physiology to promote infection. In this study, we functionally characterized the U. maydis effector protein Topless (TPL) interacting protein 6 (Tip6). We found that Tip6 interacts with the N-terminus of ZmTPL2 through its two EAR (Ethylene-responsive element binding factor-associated amphiphilic repression) motifs. We show that the EAR motifs are essential for the virulence function of Tip6 and critical for altering the nuclear distribution pattern of ZmTPL2. We propose that Tip6 mimics the recruitment of ZmTPL2 by plant repressor proteins, thus disrupting host transcriptional regulation. We show that a large group of AP2/ERF B1 subfamily transcription factors are misregulated in the presence of Tip6. Our study suggests a regulatory mechanism where the U. maydis effector Tip6 utilizes repressive domains to recruit the corepressor ZmTPL2 to disrupt the transcriptional networks of the host plant.

plant biology↗

bioRxiv2022

A fungal endophyte-generated nucleoside signal regulates host cell death and promotes root colonization

The intracellular colonization of plant roots by the beneficial fungal endophyte Serendipita indica follows a biphasic strategy. After an early biotrophic phase, the interaction transitions to a host cell death phase restricted to the epidermal and cortex layers of the root. Host cell death contributes to the successful accommodation of the fungus during the beneficial interaction in Arabidopsis thaliana. How host cell death is initiated and controlled is largely unknown. Here we show that two fungal enzymes, the ecto-5-nucleotidase SiE5NT and the nuclease SiNucA, act synergistically in the plant apoplast at the onset of cell death to produce deoxyadenosine (dAdo), a potent cell death inducer in animal systems. The uptake of extracellular dAdo, but not the structurally related adenosine (Ado), activates a previously undescribed cell death mechanism in A. thaliana. Mutation of the equilibrative nucleoside transporter ENT3 in A. thaliana results in resistance to cell death triggered by extracellular dAdo and reduced fungal-mediated cell death during root colonization. A library screen of A. thaliana T-DNA insertion lines identified a toll/interleukin-1 receptor nucleotide-binding leucine-rich repeat (TIR-NLR) protein as an additional intracellular component in dAdo-triggered cell death. Mutation of this previously uncharacterised TIR-NLR, which we have named ISI (induced by S. indica), affects host cell death, fungal colonization and growth promotion, suggesting a key role in the regulation of root cell death and plant-microbe interaction. Our data show that the combined activity of two fungal apoplastic enzymes leads to the production of a metabolite that, upon uptake, triggers TIR-NLR-modulated plant cell death, providing a link to immunometabolism in plants. Short summaryEfficient intraradical colonization by the beneficial fungal endophyte Serendipita indica requires restricted host cell death. How this symbiotic host cell death is initiated and controlled is largely unknown. Here we show that two fungal enzymes, the ecto-5-nucleotidase SiE5NT and the nuclease SiNucA, act synergistically in the apoplast at the onset of cell death to produce deoxyadenosine (dAdo), a potent cell death inducer in animal systems. Uptake of extracellular dAdo activates a previously undescribed cell death mechanism in plants. Mutation of the A. thaliana equilibrative nucleoside transporter ENT3 leads to resistance to cell death triggered by uptake of extracellular dAdo and to reduced fungal-mediated cell death during colonization. A library screen of A. thaliana T-DNA insertion lines identified a TIR-NLR protein as an additional intracellular component in dAdo-triggered cell death, providing a link to immunometabolism in plants. In a nutshellRegulated host cell death is part of the plant defense strategy against pathogens, but it is also involved in the accommodation of certain beneficial microbes in the roots. We have identified extracellular metabolites and intracellular metabolic signals that contribute to colonization by beneficial root fungal endophytes and uncovered a conserved cell death mechanism likely co-opted for establishing plant-endophyte symbiosis.

plant biology↗

bioRxiv2021

TOPLESS promotes plant immunity by repressing auxin signaling and is targeted by the fungal effector Naked1

In plants, the antagonism between growth and defense is hardwired by hormonal signaling. Perception of Pathogen Associated Molecular Patterns (PAMPs) from invading microorganisms inhibits auxin signaling and growth. Conversely, pathogens manipulate auxin signaling to promote disease, but how this hormone inhibits immunity is not fully understood. Ustilago maydis is a maize pathogen that induces auxin signaling in its host. We characterized an U. maydis effector protein, Naked1 (Nkd1), that is translocated into the host nucleus. Through its native EAR motif, Nkd1 binds to the transcriptional co-repressors TOPLESS/TOPLESS related (TPL/TPRs) and prevents the recruitment of transcriptional repressors involved in hormonal signaling, leading to de-repression of auxin and jasmonate signaling. Moderate up-regulation of auxin signaling inhibits an early defense response, PAMP-triggered ROS burst. Thus, our findings establish a clear mechanism for auxin-induced pathogen susceptibility. Manipulation of TPL by Nkd1 is evolutionary well balanced as engineered Nkd1 variants with increased expression or increased EAR-mediated TPL/TPR binding trigger typical salicylic acid mediated defense reactions, leading to pathogen resistance.

plant biology↗

bioRxiv2020

A cross-kingdom conserved ER-phagy receptor maintains endoplasmic reticulum homeostasis during stress

Eukaryotes have evolved various quality control mechanisms to promote proteostasis in the ER. Selective removal of certain ER domains via autophagy (termed as ER-phagy) has emerged as a major quality control mechanism. However, the degree to which ER-phagy is employed by other branches of ER-quality control remains largely elusive. Here, we identify a cytosolic protein, C53, that is specifically recruited to autophagosomes during ER-stress, in both plant and mammalian cells. C53 interacts with ATG8 via a distinct binding epitope, featuring a shuffled ATG8 interacting motif (sAIM). C53 senses proteotoxic stress in the ER lumen by forming a tripartite receptor complex with the ER-associated ufmylation ligase UFL1 and its membrane adaptor DDRGK1. The C53/UFL1/DDRGK1 receptor complex is activated by stalled ribosomes and induces the degradation of internal or passenger proteins in the ER. Consistently, the C53 receptor complex and ufmylation mutants are highly susceptible to ER stress. Thus, C53 forms an ancient quality control pathway that bridges selective autophagy with ribosome-associated quality control at the ER.

cell biology↗

bioRxiv2020

'Macrobot' - an automated segmentation-based system for powdery mildew disease quantification

Plant diseases, as one of the perpetual problems in agriculture, is increasingly difficult to manage due to intensifying of the field production, global trafficking, reduction of genetic variability of crops, climatic changes-driven expansion of pests, redraw and loss of effectiveness of pesticides and rapid breakdown of the disease resistance in the field. The substantial progress in genomics of both plants and pathogens, achieved in the last decades has the potential to counteract this negative trend, however, only when the genomic data is supported by relevant phenotypic data that allows linking the genomic information to specific traits. In this respect, phenotyping is and will remain an essential element of any comprehensive functional genomics study. We have developed a set of methods and equipment and combined them into a "Macrophenomics pipeline". The pipeline has been optimized for the quantification of powdery mildew infection symptoms on wheat and barley but it can be adapted to other diseases and host plants. The Macrophenomics pipeline scores the visible disease symptoms, typically 5-7 days after inoculation (dai) in a highly automated manner. The system can precisely and reproducibly quantify the percentage of the infected leaf area with a throughput of the image acquisition module of up to 10 000 individual samples per day, making it appropriate for phenotyping of large germplasms collections and crossing populations.

plant biology↗

bioRxiv2019

Fungal effector Jsi1 hijacks plant JA/ET signaling through Topless

Ustilago maydis (U. maydis) is the causal agent of maize smut disease. During the colonization process, the fungus secretes effector proteins which suppress immune responses and redirect the host-metabolism in favor of the pathogen. Here we describe a novel strategy by which U. maydis induces plant jasmonate/ethylene (JA/ET) hormone signaling and thereby biotrophic susceptibility. The U. maydis effector Jasmonate/Ethylene signaling inducer 1 (Jsi1) possesses an ethylene-responsive element binding factor-associated amphiphilic repression (EAR) motif, DLNxxP, which interacts with the second WD40 domain of the conserved plant co-repressor family Topless/Topless related (TPL/TPR). Jsi1 interaction with TPL/TPRs leads to derepression of the ethylene response factor (ERF) branch of the JA/ET signaling pathway, supporting biotrophic susceptibility. Jsi1 likely activates the ERF branch by interfering with the binding of endogenous DLNxxP motif-containing ERF transcription factors to TPL/TPR proteins. The identification of effector proteins possessing a DLNxxP motif in different fungal species with biotrophic and hemibiotrophic lifestyles together with the validation of the interaction between such effectors from Magnaporthe oryzae (M. oryzae), Sporisorium scitamineum (S. scitamineum), and S. reilianum with TPL proteins indicates the convergent evolution of effectors for modulating the TPL/TPR co-repressor hub.

plant biology↗

bioRxiv2019

The Pleiades cluster of fungal effector genes inhibit 1 host defenses

SummaryBiotrophic plant pathogens secrete effector proteins to manipulate the host physiology. Effectors suppress defenses and induce an environment favorable to disease development. Sequence-based prediction of effector function is difficulted by their rapid evolution rate. In the maize pathogen Ustilago maydis, effector-coding genes frequently organize in clusters. Here we describe the functional characterization of the pleiades, a cluster of ten symplastic effectors. Deletion of the pleiades leads to strongly impaired virulence and accumulation of reactive oxygen species (ROS) in infected tissue. Eight of the Pleiades suppress the production of ROS upon perception of pathogen associated molecular patterns (PAMPs). Although genetically redundant, the Pleiades target different host components. The paralogs Taygeta1 and Merope1 suppress ROS production in either the cytoplasm or nucleus, respectively. Merope1 targets and promotes the autoubiquitination activity of RFI2, a conserved family of E3 ligases that regulates the production of PAMP-triggered ROS burst and influences flowering time in plants.

microbiology↗

bioRxiv2019

A High-throughput Screening Method to Identify Proteins Involved in Unfolded Protein Response Signaling in Plants

BackgroundThe unfolded protein response (UPR) is a highly conserved process in eukaryotic organisms that plays a crucial role in adaptation and development. While the most ubiquitous components of this pathway have been characterized, current efforts are focused on identifying and characterizing other UPR factors that play a role in specific conditions, such as developmental changes, abiotic cues, and biotic interactions. Considering the central role of protein secretion in plant pathogen interactions, there has also been a recent focus on understanding how pathogens manipulate their hosts UPR to facilitate infection.\n\nResultsWe developed a high-throughput screening assay to identify proteins that interfere with UPR signaling in planta. A set of 35 genes from a library of secreted proteins from the maize pathogen Ustilago maydis were transiently co-expressed with a reporter construct that upregulates enhanced yellow fluorescent protein (eYFP) expression upon UPR stress in Nicotiana benthamiana plants. After UPR stress induction, leaf discs were placed in 96 well plates and eYFP expression was measured. This allowed us to identify a previously undescribed fungal protein that inhibits plant UPR signaling, which was then confirmed using the classical but more laborious qRT-PCR method.\n\nConclusionsWe have established a rapid and reliable fluorescence-based method to identify heterologously expressed proteins involved in UPR stress in plants. This system can be used for initial screens with libraries of proteins and potentially other molecules to identify candidates for further validation and characterization.

plant biology↗