In:
Science, American Association for the Advancement of Science (AAAS), Vol. 377, No. 6605 ( 2022-07-29)
Abstract:
Plants deploy intracellular nucleotide-binding leucine-rich repeat (NLR) receptors to detect pathogen effectors that are delivered to host cells during infection. Effector recognition leads to NLR oligomerization, which induces effector-triggered immunity (ETI), often involving host cell death. The NLR receptor subclass called TNL (TIR-NLR) has an N-terminal Toll/interleukin-1 receptor (TIR) signaling domain. Pathogen effector–activated TNLs form tetrameric complexes (resistosomes) with nicotinamide adenine dinucleotide hydrolase (NADase) activity encoded in the TIR domain. The NADase activity of TNLs or TIR domain proteins confers pathogen immunity and/or host cell death. Activated TNLs signal through conserved lipase-like proteins consisting of EDS1 (Enhanced Disease Susceptibility 1) and its two exclusive partners, PAD4 (Phytoalexin Deficient 4) and SAG101 (Senescence-Associated Gene 101), together with a small group of conserved coiled-coil domain–containing helper (signaling) NLRs. In Arabidopsis , EDS1-PAD4 and EDS1-SAG101 dimers cooperate with particular helper NLR subgroups, ADR1 (Activated Disease Resistance 1) and NRG1 (N requirement gene 1), respectively, to induce immune responses. The biochemical mechanisms underlying TNL and TIR dependence on these two EDS1 dimer–helper NLR modules remain unknown. RATIONALE In Arabidopsis TNL- or TIR-triggered immunity, EDS1-PAD4 dimers associate with ADR1-type helper NLRs to restrict pathogen growth, whereas EDS1-SAG101 dimers interact with NRG1-type helper NLRs to promote host cell death. Plant TNLs and TIRs catalyze production of several nucleotide-based molecules in vivo, which suggests that TIR-catalyzed products might activate immune outputs of ADR1 and NRG1. Based on similar but nonidentical EDS1-PAD4 and EDS1-SAG101 surface grooves, we hypothesized that EDS1 dimer binding of TIR NADase–catalyzed products induces association with their corresponding helper NLRs. We identified 2′-(5′′-phosphoribosyl)-5′-adenosine diphosphate (pRib-ADP) and monophosphate (pRib-AMP) as the TIR-catalyzed bioactive compounds that bind to and induce EDS1-PAD4 interaction with ADR1. However, these molecules have only weak EDS1-SAG101 binding activity, which suggests that different TIR catalytic products activate the EDS1-SAG101-NRG1 immunity branch. RESULTS We found that coexpression of an Arabidopsis TNL (RPP1) resistosome or the monocot TIR-only protein from Brachypodium distachyon with EDS1, SAG101, and NRG1 induced TNL or TIR NADase–dependent specific interaction between EDS1-SAG101 and NRG1. Coupled with high-resolution mass spectrometry (HRMS) data, a cryo–electron microscopy–generated structure of TNL-activated EDS1-SAG101 revealed that a small molecule, ADP-ribosylated adenosine triphosphate (ADPr-ATP), binds at a similar pocket as pRib-ADP and pRib-AMP to EDS1-PAD4, establishing EDS1-SAG101 as a receptor for this small molecule. ADPr-ATP binding to EDS1-SAG101 induces a conformational change in the C-terminal part of SAG101, which allosterically enables its interaction with NRG1. This mechanism is conserved in pRib-ADP– and pRib-AMP–triggered EDS1-PAD4 binding to ADR1 and explains the recruitment of helper NLR types by their corresponding EDS1 heterodimers. Residues coordinating small molecule binding in both dimers are conserved in seed plant species, suggesting broad relevance. TIR activation resulted in TIR NADase–dependent accumulation of ADPr-ATP in plant tissues. ADPr-ATP is synthesized by TIR-catalyzed transfer of ADP-ribose (ADPR) from NAD + (called ADP-ribosylation) to ATP. A related product, ADPr-ADPR (di-ADPR), with similar activity in inducing EDS1-SAG101 interaction with NRG1 is formed by ADP-ribosylation of ADPR. Synthesis of pRib-ADP and pRib-AMP likely involves a two-step mechanism through TIR-catalyzed hydrolysis of ADPr-ATP and di-ADPR. CONCLUSION TIR enzyme activity catalyzes ADP-ribosylation of ATP and ADPR to produce NAD + -derived small molecules that activate two distinctive EDS1 dimer–helper NLR immunity modules. Allosteric activation enables EDS1 dimer association with its cofunctioning helper NLR. The ligands and their receptor mechanisms are likely conserved across seed plants to regulate immune responses. TIR-catalyzed small molecules controlling two immunity branches. Activated TIRs and TNLs use NAD + or NAD + with ATP as substrates to produce ADPr-ATP and di-ADPR through ADP-ribosylation reactions, which are likely to be further hydrolyzed to pRib-ADP and pRib-AMP. pRib-ADP and pRib-AMP and ADPr-ATP and di-ADPR bind specifically to EDS1-PAD4 and EDS1-SAG101 dimers, triggering conformational changes of PAD4 and SAG101 EP domains to allosterically induce interaction with CNL-type helper NLRs, ADR1 and NRG1, for plant resistance and cell death, respectively.
Type of Medium:
Online Resource
ISSN:
0036-8075
,
1095-9203
DOI:
10.1126/science.abq8180
Language:
English
Publisher:
American Association for the Advancement of Science (AAAS)
Publication Date:
2022
detail.hit.zdb_id:
128410-1
detail.hit.zdb_id:
2066996-3
detail.hit.zdb_id:
2060783-0
SSG:
11
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