Biology subjects

Bhandari, D. D.

Publications and source records attributed to Bhandari, D. D..

4 recordsLinked to original sources

bioRxiv2019

Arabidopsis ENHANCED DISEASE RESISTANCE1 Protein Kinase Regulates the Association of ENHANCED DISEASE SUSCEPTIBILITY1 and PHYTOALEXIN DEFICIENT4 to Inhibit Cell Death

ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and PHYTOALEXIN DEFICIENT4 (PAD4) are sequence-related lipase-like proteins that function as a complex to regulate defense responses in Arabidopsis by both salicylic acid-dependent and independent pathways. Here we describe a gain-of-function mutation in PAD4 (S135F) that enhances resistance and cell death in response to infection by the powdery mildew pathogen Golovinomyces cichoracearum. The mutant PAD4 protein accumulates to wild-type levels in Arabidopsis cells, thus these phenotypes are unlikely to be due to PAD4 over accumulation. The phenotypes are similar to loss of function mutations in the protein kinase Enhanced Disease Resistance1 (EDR1), and previous work has shown that loss of PAD4 or EDS1 suppresses edr1-mediated phenotypes, placing these proteins downstream of EDR1. Here we show that EDR1 directly associates with EDS1 and PAD4 and inhibits their interaction in yeast and plant cells. We propose a model whereby EDR1 negatively regulates defense responses by interfering with the heteromeric association of EDS1 and PAD4. Our data indicate that the S135F mutation likely alters an EDS1-independent function of PAD4, potentially shedding light on a yet unknown PAD4 signaling function.

plant biology↗

bioRxiv2019

Arabidopsis PAD4 lipase-like domain is a minimal functional unit in resistance to green peach aphid

Plants have evolved mechanisms to attract beneficial microbes and insects while protecting themselves against pathogenic microbes and pests. In Arabidopsis, the immune regulator PAD4 functions with its cognate partner EDS1 to limit pathogen growth. PAD4, independently of EDS1, reduces infestation by Green Peach Aphid (GPA). How PAD4 regulates these defense outputs is unclear. By expressing the N-terminal PAD4-lipase-like domain (LLD) without its C-terminal EDS1-PAD4 (EP) domain, we interrogated PAD4 functions in plant defense. Here we show that transgenic expression of PAD4LLD in Arabidopsis is sufficient for limiting GPA infestation, but not for conferring basal and effector-triggered pathogen immunity. This suggests that the C-terminal PAD4-EP domain is necessary for EDS1-dependent immune functions. Moreover, PAD4LLD is not sufficient to interact with EDS1, indicating the PAD4-EP domain is required for heterodimerisation. These data provide molecular evidence that PAD4 has domain specific functions.

plant biology↗

bioRxiv2019

A coevolved EDS1-SAG101-NRG1 module mediates cell death signaling by TIR-domain immune receptors

Plant intracellular nucleotide-binding/leucine-rich repeat (NLR) immune receptors are activated by pathogen effectors to trigger host defenses and cell death. Toll-Interleukin1-receptor (TIR)-domain NLRs (TNLs) converge on the Enhanced Disease Susceptibility1 (EDS1) family of lipase-like proteins for all resistance outputs. In Arabidopsis TNL immunity, AtEDS1 heterodimers with Phytoalexin Deficient4 (AtPAD4) transcriptionally boost basal defense pathways. AtEDS1 uses the same surface to interact with PAD4-related Senescence-Associated Gene101 (AtSAG101), but the role of AtEDS1-AtSAG101 heterodimers was unclear. We show that AtEDS1-AtSAG101 function together with AtNRG1 coiled-coil domain helper NLRs as a coevolved TNL cell death signaling module. AtEDS1-AtSAG101-AtNRG1 cell death activity is transferable to the solanaceous species, Nicotiana benthamiana, and cannot be substituted by AtEDS1-AtPAD4 with AtNRG1 or AtEDS1-AtSAG101 with endogenous NbNRG1. Analysis of EDS1-family evolutionary rate variation and heterodimer structure-guided phenotyping of AtEDS1 variants or AtPAD4-AtSAG101 chimeras identify closely aligned -helical coil surfaces in the AtEDS1-AtSAG101 partner C-terminal domains that are necessary for TNL cell death signaling. Our data suggest that TNL-triggered cell death and pathogen growth restriction are determined by distinctive features of EDS1-SAG101 and EDS1-PAD4 complexes and that these signaling machineries coevolved with further components within plant species or clades to regulate downstream pathways in TNL immunity.

plant biology↗

bioRxiv2018

An EDS1 EP-domain surface mediating timely transcriptional reprogramming of immunity genes

Plant intracellular NLR receptors recognize pathogen interference to trigger immunity. NLR signalling mechanisms have not been resolved. Enhanced disease susceptibility 1 (EDS1) heterodimers are recruited by Toll-interleukin1-receptor domain NLRs (TNLs) to transcriptionally mobilize resistance pathways. Using an Arabidopsis EDS1 heterodimer crystal structure we interrogate the conserved but functionally uncharacterized EDS1 -helical EP-domain. We identify EP-domain positively charged residues lining a cavity that are essential for TNL immunity signalling, beyond heterodimer formation. Mutating arginine (R493) to alanine creates a weak EDS1 allele which disables TNL immunity against bacteria producing a virulence factor, coronatine (COR). Arabidopsis plants expressing EDS1R493A are slow to mobilize defence gene expression changes, independently of COR. The transcriptional delay has severe consequences for pathogen resistance and for countering bacterial COR. We uncover a set of host immunity genes whose repression by COR is blocked by wild-type EDS1 but not by EDS1R493A in the TNL response. These data uncover an EDS1 signalling surface lining the heterodimer EP-domain cavity which confers timely transcriptional reprogramming of host defence pathways and blocks bacterial virulence in NLR receptor immunity.

plant biology↗