Biology subjects

El Kasmi, F.

Publications and source records attributed to El Kasmi, F..

4 recordsLinked to original sources

bioRxiv2021

The TIR-NBS-LRR protein CSA1 is required for autoimmune cell death in Arabidopsis pattern recognition co-receptor bak1 and bir3 mutants

The BRI1-associated kinase BAK1/SERK3 is a positive regulator of multiple leucine rich receptor kinase-mediated signaling pathways including pattern triggered immunity (PTI). Absence or overexpression of BAK1 leads to spontaneous cell death formation. BAK1-interacting receptors (BIR) constitutively interact with BAK1, and plants lacking or overexpressing BIR proteins phenocopy the cell death symptoms observed in bak1 knock outs or overexpressors. In the interactome of BIR3, the TIR-NBS-LRR protein CONSTITUTIVE SHADE-AVOIDANCE 1 (CSA1) was identified by mass spectrometry. CSA1 physically interacts with BIR proteins and can be detected in complexes with BAK1. Direct interaction was shown only for CSA1 with BIR proteins but not BAK1. Double mutant bak1 bir3 genotypes develop strong dwarfism and cell death symptoms that are dependent on EDS1 and salicylic acid. Loss of CSA1 blocks bak1 and bak1 bir3-mediated cell death formation thus demonstrating that CSA1 is causal for this type of cell death. We propose that CSA1 guards BIR proteins and initiates autoimmune cell death that is observed when BAK1 BIR complexes are impaired. Our findings reveal how cell death in the absence of BAK1 and BIR3 is executed and links BAK1, a common co-receptor of many pattern recognition receptors, to NLR proteins typically implicated in effector-triggered immunity.

plant biology↗

bioRxiv2020

Arabidopsis cell surface LRR immune receptor signaling through the EDS1-PAD4-ADR1 node

Plants use both cell surface and intracellular immune receptors with leucine rich-repeat (LRRs) to detect pathogens. LRR receptor kinases (LRR-RKs) and LRR receptor-like proteins (LRR-RPs) recognize extracellular microbe-derived molecules to confer pattern-triggered immunity (PTI), while nucleotide-binding LRR (NLR) proteins detect microbial effectors inside the cell to confer effector-triggered immunity (ETI). Despite PTI and ETI signaling being initiated in different compartments, both rely on the transcriptional activation of similar sets of genes, suggesting convergence in signaling upstream of nuclear events. Here we report that two sets of molecules, helper NLRs from the ADR1 (ACTIVATED DISEASE RESISTANCE 1) family as well as lipase-like proteins EDS1 (ENHANCED DISEASE SUSCEPTIBILITY 1) and PAD4 (PHYTOALEXIN DEFICIENT 4), are required not only for ETI, but also for PTI. A further similarity is seen in the evolutionary patterns of some PTI and ETI receptor genes, with both often being highly polymorphic, and with nevertheless distinct roles of LRR-RK and LRR-RP receptors in immunity. We find that the LRR-RK SOBIR1 directly links LRR-RPs with the ADR1 helper NLR as well as EDS1 and PAD4, suggesting the formation of constitutive supramolecular signalosome complexes at the inner side of the plasma membrane. We propose that the EDS1-PAD4-ADR1 node is an essential component and convergence point for immune signaling cascades activated by both surface-resident LRR-RP receptors and intracellular NLR receptors.

plant biology↗

bioRxiv2020

Coiled-coil and RPW8-type immune receptors function at the plasma membrane in a phospholipid dependent manner

Activation of intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) results in immunity and a localized cell death response of infected cells. Cell death activity of many NLRs requires oligomerization and in some cases plasma membrane (PM) localization. However, the exact mechanisms underlying PM localization of NLRs lacking recognizable N- or C-terminal lipidation motifs or predicted transmembrane domains remains elusive. Here we show that the PM localization and stability of members of the RPW8-like coiled-coil (CCR) domain NLRs (RNLs) and a CC-type NLR (CNL) depend on the interaction with PM phospholipids. Depletion of phosphatidylinositol-4-phosphate (PI4P) from the PM led to a mislocalization of the analyzed NLRs and consequently inhibited their cell death activity. We further demonstrate activation-dependent self-association of cell death inducing RNLs. Our results provide new insights into the molecular mechanism of NLR PM localization and defines an important role of phospholipids for CNL and RNL activity during immunity.

plant biology↗

bioRxiv2020

A shortcut in forward genetics: concurrent discovery of mutant phenotype and causal mutation in Arabidopsis M2 families via MAD-mapping

ABSTRACTForward genetics is a powerful tool to establish phenotype-genotype correlations in virtually all areas of plant biology and has been particularly successful in the model plant Arabidopsis. This approach typically starts with a phenotype in an M2 mutant, followed by identifying a causal DNA change in F2 populations resulting from a cross between the mutant and a wildtype individual. Ultimately, two additional generations are needed to pinpoint causal DNA changes upon mutant identification. We postulated that genome-wide allele frequency distributions within the mutants of M2 families facilitate discrimination of causal versus non-causal mutations, essentially eliminating the need for F2 populations. In a proof-of-principle experiment, we aimed to identify signalling components employed by the executor-type resistance (R) protein, Bs4C, from pepper (Capsicum pubescens). In a native setting, Bs4C is transcriptionally activated by and mediates recognition of the transcription activator-like effector AvrBs4 from the bacterial pathogen Xanthomonas. Arabidopsis containing an estradiol-inducible Bs4C transgene was used in a conditionally lethal screen to identify second-site suppressor mutations. Whole genome sequencing was used for M2 mutant allele-frequency distribution (MAD) mapping in three independent M2 families. MAD-mapping uncovered that all three families harboured mutations in XRN4, a novel component of executor R protein pathways. Our work demonstrates that causal mutations observed in forward genetic screens can be identified immediately in M2 families instead of derived F2 families. Notably, the timesaving concept of MAD mapping should be applicable to most crop species and will advance the appeal of forward genetics beyond applications in fundamental research.SIGNIFICANCE Forward genetics has uncovered numerous genes that govern plant immune reactions. This procedure relies on mutant plants with modified immune reactions followed by identification of causal DNA changes in derived F2 progeny. We developed a novel forward genetics concept where causal DNA changes are identified in the initial M2 mutants, making time consuming establishment of F2 populations obsolete. To confirm the feasibility of the concept, we mutagenized transgenic Arabidopsis seeds containing the cell death executing resistance gene Bs4C from pepper. Whole-genome sequencing of identified mutant families that lack a Bs4C-dependent cell death revealed the XRN4 gene as a novel component of Bs4C-dependent cell death. This confirms our hypothesis that causal mutations can be identified directly within phenotypically selected mutant families.Competing Interest StatementThe authors have declared no competing interest.View Full Text

plant biology↗