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Golovko, Anna; Sitbon, Folke; Tillberg, Elisabeth; Nicander, Björn

doi:10.1023/a:1014958816241

Cited by 57 publications

(18 citation statements)

References 20 publications

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“…Predominant accumulation of iP nucleotides in AtIPT8-overexpressing Arabidopsis was also reported (34). Induction of AtIPT2 expression did not increase the level of any CK species because it catalyzes prenylation of tRNA (33). These results suggest that AtIPTs principally use DMAPP, but not HMBDP, for the biosynthesis of CKs in planta, regardless of their subcellular localization.…”

Section: Resultssupporting

confidence: 54%

Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant

Sakakibara

Kasahara

Ueda

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

104

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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, transzeatin-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.crown gall ͉ isopentenyltransferase ͉ methylerythritol phosphate pathway C ytokinins (CKs) are a group of plant hormones essential for cell division and differentiation in plants (1). Most natural CKs, including isopentenyladenine (iP) and trans-zeatin (tZ) (Fig. 1), are derivatives of N 6 -prenylated adenine (1). The prenyl side chain of CKs can be derived from the methylerythritol phosphate (MEP) pathway or the mevalonate (MVA) pathway, both of which supply common C 5 units for isoprenoid biosynthesis (2, 3). The MEP pathway widely occurs in the bacterial kingdom and the plastids of plants, whereas the MVA pathway is commonly found in the cytosol of eukaryotes (2, 3). Thus, plants have the two different isoprenoid pathways in separate subcellular compartments. Recent work has shown that the majority of the prenyl side chain of iP and tZ is derived from the MEP pathway in Arabidopsis seedlings (4).To initiate CK biosynthesis, an isoprenoid precursor is transferred to AMP, ADP or ATP by adenosine phosphateisopentenyltransferase (IPT, EC 2.5.1.27) ( Fig. 1) (5-7). At least two routes have been proposed for the formation of tZ, an active CK, in plants. In the conventional iP riboside 5Ј-monophosphate (iPRMP)-dependent pathway, dimethylallyl diphosphate (DMAPP) is used as the side chain precursor for iPRMP, which is then converted to tZ riboside 5Ј-monophosphate (tZRMP) by P450 monooxygenases (8) (CYP735A1 and CYP735A2 in Arabidopsis; Fig. 1). The other proposed pathway is an iPRMPindependent bypass, in which an unidentified hydroxylated derivative of DMAPP is directly transferred to the adenine moiety (9). A candidate for this putative substrate is 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (HMBDP) (10), which has recently been shown to occur as an int...

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Section: Resultssupporting

confidence: 54%

Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant

Sakakibara

Kasahara

Ueda

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

104

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“…AtIPT2 and AtIPT9 resemble tRNA IPTs in their amino acid sequences (20,23,24), and AtIPT2 indeed suppresses the phenotypes of a Saccharomyces cerevisiae mutant lacking a tRNA IPT (34). We measured cZR, tZR, and iPR contents in tRNA hydrolysates from WT and IPT mutants.…”

Section: Discussionmentioning

confidence: 99%

“…In bacteria, modified tRNAs are a source of low-level cytokinin production (31,32); however, there is no experimental evidence for a tRNA-degradation route for cZ production in plants. tRNA IPTs catalyze isopentenylation of certain tRNAs in diverse organisms ranging from bacteria to animals and plants (33), including Arabidopsis (34). In the case of the bacterium Salmonella typhimurium, the isopentenyl chain of tRNA is hydroxylated at the cis position by the miaE gene product (35).…”

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confidence: 99%

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Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

Miyawaki

Tarkowski

Matsumoto-Kitano

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

495

534

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Cytokinins, which are central regulators of cell division and differentiation in plants, are adenine derivatives carrying an isopentenyl side chain that may be hydroxylated. Plants have two classes of isopentenyltransferases (IPTs) acting on the adenine moiety: ATP͞ ADP isopentenyltransferases (in Arabidopsis thaliana, AtIPT1, 3, 4 -8) and tRNA IPTs (in Arabidopsis, AtIPT2 and 9). ATP͞ADP IPTs are likely to be responsible for the bulk of cytokinin synthesis, whereas it is thought that cis-zeatin (cZ)-type cytokinins are produced possibly by degradation of cis-hydroxy isopentenyl tRNAs, which are formed by tRNA IPTs. However, these routes are largely hypothetical because of lack of in vivo evidence, because the critical experiment necessary to verify these routes, namely the production and analysis of mutants lacking AtIPTs, has not yet been described. We isolated null mutants for all members of the ATP͞ADP IPT and tRNA IPT gene families in Arabidopsis. Notably, our work demonstrates that the atipt1 3 5 7 quadruple mutant possesses severely decreased levels of isopentenyladenine and trans-zeatin (tZ), and their corresponding ribosides, ribotides, and glucosides, and is retarded in its growth. In contrast, these mutants possessed increased levels of cZ-type cytokinins. The atipt2 9 double mutant, on the other hand, lacked isopentenyl-and cishydroxy isopentenyl-tRNA, and cZ-type cytokinins. These results indicate that whereas ATP͞ADP IPTs are responsible for the bulk of isopentenyladenine-and tZ-type cytokinin synthesis, tRNA IPTs are required for cZ-type cytokinin production. This work clarifies the long-standing questions of the biosynthetic routes for isopentenyladenine-, tZ-, and cZ-type cytokinin production.S ince the discovery of cytokinins as inducers of plant cell division (1) and differentiation (2), they have been recognized as central regulators of plant development (3). Cytokinins also increase nutrient sink strength, delay senescence, stimulate outgrowth from lateral buds, and inhibit cell elongation (4). The important roles for cytokinins in cell division were verified by overexpression of genes for cytokinin-degrading enzymes (cytokinin oxidases, CKXs) (5-7) and by examination of single and higher-order cytokinin-receptor null mutants (8-10).Most naturally occurring cytokinins are N 6 -isopentenyladenine (iP) derivatives. iP carries an unmodified isopentenyl side chain, whereas trans-zeatin (tZ) and cis-zeatin (cZ) carry hydroxylated side chains. Cytokinins exist in free-base, riboside, and ribotide forms, with varying degrees of biological activity. Cytokinins also may be modified in several ways. For example, the N7 and N9 positions of the adenine moiety of cytokinins may be glucosylated to form N-glucosides. Alternatively, the hydroxyl group of tZ and cZ may be glucosylated or xylosylated to form zeatin-O-glucosides or zeatin-O-xylosides. N-and O-glycosides are biologically inactive (3).Experimental evidence demonstrates that free-base cytokinins are biologically active. For example, iP (11) and t...

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“…2000; Golovko et al. 2002). The cytoskeleton pathway has also been shown to play an essential role in the normal growth and development of trichomes (Folkers et al.…”

Section: Discussionmentioning

confidence: 99%

Adaptional evolution of trichome in Caragana korshinskii to natural drought stress on the Loess Plateau, China

Ning

Wang

Zhou

et al. 2016

Ecology and Evolution

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Caragana korshinskii is commonly employed to improve drought ecosystems on the Loess Plateau, although the molecular mechanism at work is poorly understood, particularly in terms of the plant's ability to tolerate drought stress. Water is the most severe limiting factor for plant growth on the Loess Plateau. The trichome is known to play an efficient role in reducing water loss through decreasing the rate of transpiration, so in this study, we focused on the trichome‐related gene expression of ecological adaptation in C. korshinskii under low precipitation conditions. In order to explore the responses of trichomes to drought, we selected two experimental sites from wet to dry along the Loess Plateau latitude gradient for observation. Micro‐phenomena through which trichomes grew denser and larger under reduced precipitation were observed using a scanning electron microscope; de novo transcriptomes and quantitative PCR were then used to explore and verify gene expression patterns of C. korshinskii trichomes. Results showed that GIS2,TTG1, and GL2 were upregulated (as key positive‐regulated genes on trichome development), while CPC was downregulated (negative‐regulated gene). Taken together, our data indicate that downstream genes of gibberellin and cytokinin signaling pathways, alongside several cytoskeleton‐related genes, contribute to modulating trichome development to enhance transpiration resistance ability and increase the resistance to drought stress in C. korshinskii.

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Cited by 57 publications

References 20 publications

Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant

Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant

Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

Adaptional evolution of trichome in Caragana korshinskii to natural drought stress on the Loess Plateau, China

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