Page 117 - PC2019 Program & Proceedings

PLANT CANADA 2019

S19. The MACPF protein CAD1 is guarded by the plant immune system
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2
1
1
*1
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Sementchoukova, I. ; D. Holmes ; M. Bredow ; K. Siegal ; K. Thor ; S. Pascetta ; C. Zipfel ;
2
1
J. Monaghan
1 Queen's University
2 University of East Anglia
Plant pathogens secrete effector proteins into host cells that target key components of immune
signaling in order to shut down plant defenses. To protect against effector sabotage, intracellular
NUCLEOTIDE BINDING AND LEUCINE RICH REPEAT RECEPTORS (NLRs) ‘guard’ the integrity
of host immune proteins that are targeted during pathogenesis. NLR activation typically trig05/gers a
form of localized programmed cell death known as the hypersensitive response (HR) that limits
pathogen proliferation. Few NLRs have however been matched to their host or pathogen targets. Here, we
investigate whether the Arabidopsis thaliana MEMBRANE ATTACK COMPLEX/PERFORIN
(MACPF) protein CONSTITUTIVE ACTIVE DEFENSE 1 (CAD1) is guarded by plant NLRs as its loss
of function leads to autoimmunity. We utilize a novel cad1 allele that, similar to null alleles, results in
enhanced EDS1-dependent immune signaling, and conducted a screen to identify NLRs that may be
involved in cad1 autoimmunity. Our analysis provides novel insight into the molecular aspects of host-
pathogen recognition.

Irina Sementchoukova (17is12@queensu.ca)

S20. Sub-functionalization of the calcium-dependent protein kinase CPK28 by site-specific
phosphorylation
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2
1
*1
Bredow, M. ; K. Bender ; D. Holmes ; A. Thomson ; A. Johnson-Dingee ; S. Huber ;
3
1
J. Monaghan 1
1 Queen's University
2 University of Zurich
3 University of Illinois-Urbana-Champaign
Plant innate immunity relies on the detection of pathogens at the cell surface which initiates intracellular
signaling, culminating in broad-spectrum resistance. Immune signaling must be tightly regulated to
safeguard against cellular damage. The Arabidopsis thaliana calcium-dependent protein kinase CPK28
negatively regulates early immune signaling by promoting degradation of the immune kinase
BOTRYTIS-INDUCED KINASE 1 (BIK1). cpk28 loss-of-function plants display enhanced immune
function with no compromise to vegetative growth. However, CPK28 additionally functions in the
transition to reproductive growth, as cpk28 mutants display stunted stem elongation. Here, we explored
site-specific phosphorylation as a mechanism for directing the activity of CPK28 in these two signaling
pathways. Phosphoablative serine/threonine-to-alanine mutant lines were generated for previously
identified in vivo autophosphorylation sites and BIK1 in vitro transphosphorylation sites identified on the
rice ortholog of CPK28. We identified a single phosphorylation site that is uniquely required for CPK28-
mediated immune homeostasis but is dispensable for CPK28-mediated reproductive stage transition.
Ablation of this site resulted in higher calcium requirements for in vitro auto- and trans-phosphorylation
activity. Our cumulative evidence suggests a role for phosphorylation at this site in “priming” CPK28
activation following immune-induced calcium influx. This work provides novel insight into the regulation
of CPK28 which can be used for the biotechnological development of disease resistant crops without
consequences to yield.

Melissa Bredow (11mb95@queensu.ca)

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