Identification of Rhodococcus fascians cytokinins and their modus operandi to reshape the plant.
Decades ago, the importance of cytokinins (CKs) during Rhodococcus fascians pathology had been acknowledged, and an isopentenyltransferase gene had been characterized in the fas operon of the linear virulence plasmid, but hitherto, no specific CK(s) could be associated with virulence. We show that the CK receptors AHK3 and AHK4 of Arabidopsis thaliana are essential for symptom development, and that the CK perception machinery is induced upon infection, underlining its central role in the symptomatology. Three classical CKs [isopentenyladenine, trans-zeatin, and cis-zeatin (cZ)] and their 2-methylthio (2MeS)-derivatives were identified by CK profiling of both the pathogenic R. fascians strain D188 and its nonpathogenic derivative D188-5. However, the much higher CK levels in strain D188 suggest that the linear plasmid is responsible for the virulence-associated production. All R. fascians CKs were recognized by AHK3 and AHK4, and, although they individually provoked typical CK responses in several bioassays, the mixture of bacterial CKs exhibited clear synergistic effects. The cis- and 2MeS-derivatives were poor substrates of the apoplastic CK oxidase/dehydrogenase enzymes and the latter were not cytotoxic at high concentrations. Consequently, the accumulating 2MeScZ (and cZ) in infected Arabidopsis tissue contribute to the continuous stimulation of tissue proliferation. Based on these results, we postulate that the R. fascians pathology is based on the local and persistent secretion of an array of CKs.
Pertry
Ine
I
Department of Plant Systems Biology, Flanders Institute for Biotechnology, Technologiepark 927, 9052 Gent, Belgium.
Václavíková
Katerina
K
Depuydt
Stephen
S
Galuszka
Petr
P
Spíchal
Lukás
L
Temmerman
Wim
W
Stes
Elisabeth
E
Schmülling
Thomas
T
Kakimoto
Tatsuo
T
Van Montagu
Marc C E
MC
Strnad
Miroslav
M
Holsters
Marcelle
M
Tarkowski
Petr
P
Vereecke
Danny
D
D017360:Arabidopsis / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000502:physiology; D003583:Cytokinins / Q000032:analysis; D000071677:Histidine Kinase; D006706:Homeostasis; D011494:Protein Kinases / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology; D012240:Rhodococcus / Q000472:pathogenicity*; D014774:Virulence
D029681:Arabidopsis Proteins; D003583:Cytokinins; D011956:Receptors, Cell Surface; D011494:Protein Kinases; D000071677:Histidine Kinase; C000605493:AHK3 protein, Arabidopsis; C421783:WOL protein, Arabidopsis