RRC ID 41122
Author Radhika V, Ueda N, Tsuboi Y, Kojima M, Kikuchi J, Kudo T, Sakakibara H.
Title Methylated Cytokinins from the Phytopathogen Rhodococcus fascians Mimic Plant Hormone Activity.
Journal Plant Physiol
Abstract Cytokinins (CKs), a class of phytohormones that regulate plant growth and development, are also synthesized by some phytopathogens to disrupt the hormonal balance and to facilitate niche establishment in their hosts. Rhodococcus fascians harbors the fasciation (fas) locus, an operon encoding several genes homologous to CK biosynthesis and metabolism. This pathogen causes unique leafy gall symptoms reminiscent of CK overproduction; however, bacterial CKs have not been clearly correlated with the severe symptoms, and no virulence-associated unique CKs or analogs have been identified. Here, we report the identification of monomethylated N(6)-(∆(2)-isopentenyl)adenine and dimethylated N(6)-(∆(2)-isopentenyl)adenine (collectively, methylated cytokinins [MeCKs]) from R. fascians. MeCKs were recognized by a CK receptor and up-regulated type-A ARABIDOPSIS THALIANA RESPONSE REGULATOR genes. Treatment with MeCKs inhibited root growth, a hallmark of CK action, whereas the receptor mutant was insensitive. MeCKs were retained longer in planta than canonical CKs and were poor substrates for a CK oxidase/dehydrogenase, suggesting enhanced biological stability. MeCKs were synthesized by S-adenosyl methionine-dependent methyltransferases (MT1 and MT2) that are present upstream of the fas genes. The best substrate for methylation was isopentenyl diphosphate. MT1 and MT2 catalyzed distinct methylation reactions; only the MT2 product was used by FAS4 to synthesize monomethylated N(6)-(∆(2)-isopentenyl)adenine. The MT1 product was dimethylated by MT2 and used as a substrate by FAS4 to produce dimethylated N(6)-(∆(2)-isopentenyl)adenine. Chemically synthesized MeCKs were comparable in activity. Our results strongly suggest that MeCKs function as CK mimics and play a role in this plant-pathogen interaction.
Volume 169(2)
Pages 1118-26
Published 2015-10-1
DOI 10.1104/pp.15.00787
PII pp.15.00787
PMID 26251309
PMC PMC4587462
MeSH Arabidopsis / drug effects Arabidopsis / microbiology* Cytokinins / chemistry* Cytokinins / metabolism* Cytokinins / pharmacology Host-Pathogen Interactions* Isopentenyladenosine / chemistry Isopentenyladenosine / metabolism Methylation Molecular Mimicry Molecular Structure Plant Roots / drug effects Plant Roots / growth & development Rhodococcus / metabolism Rhodococcus / pathogenicity*
IF 6.305
Times Cited 30
General Microbes JCM 6162