More Like this

1. Dual Role of Auxin in Regulating Plant Defense and Bacterial Virulence Gene Expression During Pseudomonas syringae PtoDC3000 Pathogenesis

   https://doi.org/10.1094/MPMI-02-20-0047-R  

   Djami-Tchatchou, Arnaud T. ; Harrison, Gregory A. ; Harper, Chris P. ; Wang, Renhou ; Prigge, Michael J. ; Estelle, Mark ; Kunkel, Barbara N. ( August 2020 , Molecular Plant-Microbe Interactions®)

   null (Ed.)

   Modification of host hormone biology is a common strategy used by plant pathogens to promote disease. For example, the bacterial pathogen strain Pseudomonas syringae DC3000 (PtoDC3000) produces the plant hormone auxin (indole-3-acetic acid [IAA]) to promote PtoDC3000 growth in plant tissue. Previous studies suggest that auxin may promote PtoDC3000 pathogenesis through multiple mechanisms, including both suppression of salicylic acid (SA)-mediated host defenses and via an unknown mechanism that appears to be independent of SA. To test if host auxin signaling is important during pathogenesis, we took advantage of Arabidopsis thaliana lines impaired in either auxin signaling or perception. We found that disruption of auxin signaling in plants expressing an inducible dominant axr2-1 mutation resulted in decreased bacterial growth and that this phenotype was suppressed by introducing the sid2-2 mutation, which impairs SA synthesis. Thus, host auxin signaling is required for normal susceptibility to PtoDC3000 and is involved in suppressing SA-mediated defenses. Unexpectedly, tir1 afb1 afb4 afb5 quadruple-mutant plants lacking four of the six known auxin coreceptors that exhibit decreased auxin perception, supported increased levels of bacterial growth. This mutant exhibited elevated IAA levels and reduced SA-mediated defenses, providing additional evidence that auxin promotes disease by suppressing host defense. We also investigated the hypothesis that IAA promotes PtoDC3000 virulence through a direct effect on the pathogen and found that IAA modulates expression of virulence genes, both in culture and in planta. Thus, in addition to suppressing host defenses, IAA acts as a microbial signaling molecule that regulates bacterial virulence gene expression. 

   more » « less
2. Involvement of Arabidopsis Acyl Carrier Protein 1 in PAMP-triggered immunity

   https://doi.org/10.1094/MPMI-02-22-0049-R  

   Zhao, Zhenzhen ; Fan, Jiangbo ; Yang, Piao ; Wang, Zonghua ; Stephen, Opiyo ; Mackey, David ; Ye, Xia ( January 2022 , Molecular Plant-Microbe Interactions®)

   Plant fatty acids (FAs) and lipids are essential in storing energy and act as structural components for cell membranes and signaling molecules for plant growth and stress responses. Acyl Carrier Proteins (ACPs) are small acidic proteins that covalently bind the fatty acyl intermediates during the elongation of FAs. The Arabidopsis thaliana ACP family has eight members. Through reverse genetic, molecular, and biochemical approaches, we have discovered that ACP1 localizes to the chloroplast and limits the magnitude of pattern-triggered immunity (PTI) against the bacterial pathogen Pseudomonas syringae pathovar tomato (Pto). The mutant acp1 plants have reduced levels of linolenic acid (18:3), which is the primary precursor for the biosynthesis of the phytohormone jasmonic acid (JA), and a corresponding decrease in the abundance of JA. Consistent with the known antagonistic relationship between JA and salicylic acid (SA), acp1 mutant plants also accumulate higher level of SA and display the corresponding shifts in JA- and SA-regulated transcriptional outputs. Moreover, the methyl JA and linolenic acid treatments cause an apparently enhanced decrease of resistance against Pto in acp1 mutants than that in wild-type plants. The ability of ACP1 to prevent this hormone imbalance likely underlies its negative impact on PTI in plant defense. Thus, ACP1 links FA metabolism to stress hormone homeostasis to be negatively involved in PTI in Arabidopsis plant defense. 

   more » « less
3. Arabidopsis PIC30 encodes a major facilitator superfamily transporter responsible for the uptake of picolinate herbicides

   https://doi.org/10.1111/tpj.14608  

   Kathare, Praveen K. ; Dharmasiri, Sunethra ; Vincill, Eric D. ; Routray, Pratyush ; Ahmad, Idrees ; Roberts, Daniel M. ; Dharmasiri, Nihal ( February 2020 , The Plant Journal)

   Picloram is an auxinic herbicide that is widely used for controlling broad leaf weeds. However, its mechanism of transport into plants is poorly understood. In a genetic screen for picloram resistance, we identified three Arabidopsis mutant alleles ofPIC30(PICLORAM RESISTANT30) that are specifically resistant to picolinates, but not to other auxins.PIC30is a previously uncharacterized gene that encodes a major facilitator superfamily (MFS) transporter. Similar to most members of MFS, PIC30 contains 12 putative transmembrane domains, and PIC30‐GFP fusion protein selectively localizes to the plasma membrane.In plantatransport assays demonstrate that PIC30 specifically transports picloram, but not indole‐3‐acetic acid (IAA). Functional analysis ofXenopus laevisoocytes injected with PIC30 cRNA demonstrated PIC30 mediated transport of picloram and several anions, including nitrate and chloride. Consistent with these roles of PIC30, three allelicpic30mutants are selectively insensitive to picolinate herbicides, whilepic30‐3is also defective in chlorate (analogue of nitrate) transport and also shows reduced uptake of. Overexpression ofPIC30fully complements both picloram and chlorate insensitive phenotypes ofpic30‐3. Despite the continued use of picloram as an herbicide, a transporter for picloram was not known until now. This work provides insight into the mechanisms of plant resistance to picolinate herbicides and also shed light on the possible endogenous function of PIC30 protein.

    

   more » « less
4. Selective auxin agonists induce specific AUX/IAA protein degradation to modulate plant development

   https://doi.org/10.1073/pnas.1809037116  

   Vain, Thomas ; Raggi, Sara ; Ferro, Noel ; Barange, Deepak Kumar ; Kieffer, Martin ; Ma, Qian ; Doyle, Siamsa M. ; Thelander, Mattias ; Pařízková, Barbora ; Novák, Ondřej ; et al ( March 2019 , Proceedings of the National Academy of Sciences)

   Auxin phytohormones control most aspects of plant development through a complex and interconnected signaling network. In the presence of auxin, AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) transcriptional repressors are targeted for degradation by the SKP1-CULLIN1-F-BOX (SCF) ubiquitin-protein ligases containing TRANSPORT INHIBITOR RESISTANT 1/AUXIN SIGNALING F-BOX (TIR1/AFB). CULLIN1-neddylation is required for SCF^TIR1/AFBfunctionality, as exemplified by mutants deficient in the NEDD8-activating enzyme subunit AUXIN-RESISTANT 1 (AXR1). Here, we report a chemical biology screen that identifies small molecules requiring AXR1 to modulate plant development. We selected four molecules of interest, RubNeddin 1 to 4 (RN1 to -4), among which RN3 and RN4 trigger selective auxin responses at transcriptional, biochemical, and morphological levels. This selective activity is explained by their ability to consistently promote the interaction between TIR1 and a specific subset of AUX/IAA proteins, stimulating the degradation of particular AUX/IAA combinations. Finally, we performed a genetic screen using RN4, the RN with the greatest potential for dissecting auxin perception, which revealed that the chromatin remodeling ATPase BRAHMA is implicated in auxin-mediated apical hook development. These results demonstrate the power of selective auxin agonists to dissect auxin perception for plant developmental functions, as well as offering opportunities to discover new molecular players involved in auxin responses.

    

   more » « less
5. Pseudomonas syringae effector HopZ3 suppresses the bacterial AvrPto1– tomato PTO immune complex via acetylation

   Jeleńska, J. ; Lee, J. ; Manning, A.J. ; Wolfgeher, D.J. ; Ahn, Y. ; Walters-Marrah, G. ; Lopez, I.E. ; Garcia, L. ; Sheri A. McClerklin, S.A. ; Michelmore, R.W. ; et al ( January 2021 , PLOS pathogens)

   null (Ed.)

   The plant pathogen Pseudomonas syringae secretes multiple effectors that modulate plant defenses. Some effectors trigger defenses due to specific recognition by plant immune complexes, whereas others can suppress the resulting immune responses. The HopZ3 effector of P. syringae pv. syringae B728a (PsyB728a) is an acetyltransferase that modifies not only components of plant immune complexes, but also the Psy effectors that activate these complexes. In Arabidopsis, HopZ3 acetylates the host RPM1 complex and the Psy effectors AvrRpm1 and AvrB3. This study focuses on the role of HopZ3 during tomato infection. In Psy-resistant tomato, the main immune complex includes PRF and PTO, a RIPK-family kinase that recognizes the AvrPto effector. HopZ3 acts as avirulence factor on tomato by suppressing AvrPto1Psy-triggered immunity. HopZ3acetylates AvrPto1Psy and the host proteins PTO, SlRIPK and SlRIN4s. Biochemical reconstruction and site-directed mutagenesis experiments suggest that acetylation acts in multiple ways to suppress immune signaling in tomato. First, acetylation disrupts the critical AvrPto1Psy-PTO interaction needed to initiate the immune response. Unmodified residues at the binding interface of both proteins and at other residues needed for binding are acetylated. Second, acetylation occurs at residues important for AvrPto1Psy function but not for binding to PTO. Finally, acetylation reduces specific phosphorylations needed for promoting the immune-inducing activity of HopZ3’s targets such as AvrPto1Psy and PTO. In some cases, acetylation competes with phosphorylation. HopZ3-mediated acetylation suppresses the kinase activity of SlRIPK and the phosphorylation of its SlRIN4 substrate previously implicated in PTO-signaling. Thus, HopZ3 disrupts the functions of multiple immune components and the effectors that trigger them, leading to increased susceptibility to infection. Finally, mass 44 spectrometry used to map specific acetylated residues confirmed HopZ3’s unusual capacity to modify histidine in addition to serine, threonine and lysine residues. 

   more » « less