Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant.
Agrobacterium tumefaciens infects plants and induces the formation of tumors called "crown galls" by integrating the transferred-DNA (T-DNA) region of the Ti-plasmid into the plant nuclear genome. Tumors are formed because the T-DNA encodes enzymes that modify the synthesis of two plant growth hormones, auxin and cytokinin (CK). Here, we show that a CK biosynthesis enzyme, Tmr, which is encoded by the Agrobacterium T-DNA region, is targeted to and functions in plastids of infected plant cells, despite having no typical plastid-targeting sequence. Evidence is provided that Tmr is an adenosine phosphate-isopentenyltransferase (IPT) that creates a new CK biosynthesis bypass by using 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (HMBDP) as a substrate. Unlike in the conventional CK biosynthesis pathway in plants, trans-zeatin-type CKs are produced directly without the requirement for P450 monooxygenase-mediated hydroxylation. Consistent with the plastid localization of Tmr, HMBDP is an intermediate in the methylerythritol phosphate pathway, a plastid-localized biosynthesis route for universal isoprenoid precursors. These results demonstrate that A. tumefaciens modifies CK biosynthesis by sending a key enzyme into plastids of the host plant to promote tumorigenesis.
Sakakibara
Hitoshi
H
Laboratories for Communication Mechanisms and Cellular Growth and Development, Plant Science Center, RIKEN, Suehiro 1-7-22, Tsurumi, Yokohama 230-0045, Japan. sakaki@postman.riken.go.jp
Kasahara
Hiroyuki
H
Ueda
Nanae
N
Kojima
Mikiko
M
Takei
Kentaro
K
Hishiyama
Shojiro
S
Asami
Tadao
T
Okada
Kazunori
K
Kamiya
Yuji
Y
Yamaya
Tomoyuki
T
Yamaguchi
Shinjiro
S
D000227:Adenine Nucleotides / Q000378:metabolism; D016960:Agrobacterium tumefaciens / Q000201:enzymology*; D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D017360:Arabidopsis / Q000382:microbiology*; D001426:Bacterial Proteins / Q000378:metabolism*; D015153:Blotting, Western; D003583:Cytokinins / Q000096:biosynthesis*; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D015513:Oncogene Proteins / Q000378:metabolism*; D010755:Organophosphates / Q000378:metabolism; D036741:Plant Tumor-Inducing Plasmids / Q000235:genetics*; D010941:Plant Tumors / Q000235:genetics* / Q000382:microbiology
C467061:4-hydroxy-3-methyl-2-butenyl diphosphate; D000227:Adenine Nucleotides; D001426:Bacterial Proteins; D003583:Cytokinins; C112234:LSO protein, Agrobacterium tumefaciens; D015513:Oncogene Proteins; D010755:Organophosphates; D049452:Green Fluorescent Proteins; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase