Endoplasmic reticulum-quality control chaperones facilitate the biogenesis of Cf receptor-like proteins involved in pathogen resistance of tomato.
Cf proteins are receptor-like proteins (RLPs) that mediate resistance of tomato (Solanum lycopersicum) to the foliar pathogen Cladosporium fulvum. These transmembrane immune receptors, which carry extracellular leucine-rich repeats that are subjected to posttranslational glycosylation, perceive effectors of the pathogen and trigger a defense response that results in plant resistance. To identify proteins required for the functionality of these RLPs, we performed immunopurification of a functional Cf-4-enhanced green fluorescent protein fusion protein transiently expressed in Nicotiana benthamiana, followed by mass spectrometry. The endoplasmic reticulum (ER) heat shock protein70 binding proteins (BiPs) and lectin-type calreticulins (CRTs), which are chaperones involved in ER-quality control, were copurifying with Cf-4-enhanced green fluorescent protein. The tomato and N. benthamiana genomes encode four BiP homologs and silencing experiments revealed that these BiPs are important for overall plant viability. For the three tomato CRTs, virus-induced gene silencing targeting the plant-specific CRT3a gene resulted in a significantly compromised Cf-4-mediated defense response and loss of full resistance to C. fulvum. We show that upon knockdown of CRT3a the Cf-4 protein accumulated, but the pool of Cf-4 protein carrying complex-type N-linked glycans was largely reduced. Together, our study on proteins required for Cf function reveals an important role for the CRT ER chaperone CRT3a in the biogenesis and functionality of this type of RLP involved in plant defense.
Laboratory of Phytopathology, Wageningen University, 6708 PB Wageningen, The Netherlands.
Thomas W H
TW
Liebrand
Patrick
P
Smit
Ahmed
A
Abd-El-Haliem
Ronnie
R
de Jonge
Jan H G
JH
Cordewener
Antoine H P
AH
America
Jan
J
Sklenar
Alexandra M E
AM
Jones
Silke
S
Robatzek
Bart P H J
BP
Thomma
Wladimir I L
WI
Tameling
Matthieu H A J
MH
Joosten
D000595:Amino Acid Sequence; D002963:Cladosporium / Q000502:physiology; D060467:Disease Resistance; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D020868:Gene Silencing; D006031:Glycosylation; D049452:Green Fluorescent Proteins / Q000302:isolation & purification; D018551:Solanum lycopersicum / Q000378:metabolism* / Q000382:microbiology*; D018832:Molecular Chaperones / Q000378:metabolism*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D030821:Plants, Genetically Modified; D011134:Polysaccharides / Q000378:metabolism; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000235:genetics; D014170:Transformation, Genetic
D018832:Molecular Chaperones; D010940:Plant Proteins; D011134:Polysaccharides; D011993:Recombinant Fusion Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins