Overexpression of a petunia zinc‐finger gene alters cytokinin metabolism and plant forms

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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“…Extraction and determination of CKs from transgenic Arabidopsis lines overexpressing IPTs were performed as described (27).…”

Section: Methodsmentioning

confidence: 99%

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.

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105

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“…The outgrowth phenotype of the bud2 axillary buds may also result from altered cytokinin biosynthesis and/ or response, because cytokinin has long been proposed as a secondary messenger of IAA in controlling shoot branching [63][64][65]. We therefore compared the endogenous levels of various cytokinins between bud2-2 and wild-type seedlings.…”

Section: Altered Biosynthesis Of Cytokinins In Bud2 Plantsmentioning

confidence: 99%

“…Extraction and purification of cytokinin were carried out as described previously [78,79] After extraction and SPE purification, cytokinins were analyzed on a liquid chromatography-tandem mass spectrometry system (Finnigan Surveyor LC-LCQ Deca XP MAX, Thermo, San Jose, CA, USA) using positive ion electrospray ionization and quantified as described previously [63].…”

Section: Cytokinin Measurementmentioning

confidence: 99%

The BUD2 mutation affects plant architecture through altering cytokinin and auxin responses in Arabidopsis

et al. 2010

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The ratio of auxin and cytokinin plays a crucial role in regulating aerial architecture by promoting or repressing axillary bud outgrowth. We have previously identified an Arabidopsis mutant bud2 that displays altered root and shoot architecture, which results from the loss-of-function of S-adenosylmethionine decarboxylase 4 (SAMDC4). In this study, we demonstrate that BUD2 could be induced by auxin, and the induction is dependent on auxin signaling. The mutation of BUD2 results in hyposensitivity to auxin and hypersensitivity to cytokinin, which is confirmed by callus induction assays. Our study suggests that polyamines may play their roles in regulating the plant architecture through affecting the homeostasis of cytokinins and sensitivities to auxin and cytokinin. IntroductionPolyamines, including diamine putrescine, triamine spermidine and tetraamine spermine, are low-molecularmass organic cations. They exist widely in all living organisms and are essential for their survival, because blocking of the biosynthesis of polyamines leads to lethal phenotypes in animals [1] and higher plants [2][3][4]. In higher plants, polyamines have been proposed to function in response to environmental stresses and in regulating growth and development [4][5][6][7][8][9][10][11]. Plant molecular and physiological studies over past decades have shown that higher plants defective in producing polyamines often have altered plant architecture, with reduced plant height or more branches in shoots and roots [4,[10][11][12][13]. However, the underlying mechanisms still remain largely elusive.Branches of higher plants originate from the axillary meristems (AMs) of shoots, and formation of a branch generally consists of the initiation of a new AM and its subsequent outgrowth. However, an AM may arrest its growth under some conditions, forming a dormant bud. The dormant buds will release their outgrowth once they sense a permissible environmental or developmental signal. In many plant species, axillary buds become dormant due to the inhibiting effects of the primary shoot apex on the outgrowth of AMs, a phenomenon known as 'apical dominance'. Auxin was first regarded as a direct regulator in this process [14], a notion strengthened thereafter by physiological studies on decapitated shoot apices [15][16][17], and by analyzing auxin biosynthesis, transport and signaling [18][19][20][21][22][23][24][25][26][27][28][29] in plants. However, when radiolabelled auxin was applied to a decapitated stump, the outgrowth of axillary buds was inhibited even though radiolabelled auxin was not found to accumulate in axillary buds, suggesting an indirect suppression effect of auxin on the AM outgrowth [28,30] and the presence of second messengers.Cytokinin has been proposed as a second messenger that mediates the action of auxin in controlling the apical dominance, because it promotes the outgrowth of lateral buds when directly applied to buds [31]. Although an antagonistic role of auxin and cytokinin in the regulation of apical dominance has been postu...

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“…It was also noteworthy that all explants of the first subculture had the apical bud. Apical meristems have been reported as auxin producer centers (Nakagawa et al, 2005), therefore a higher content of the endogenous auxin could explain the extended effect of BA (0.1 and 0.5 mg.L -1 , see Fig. 2a and 2c) during the subculture 1.…”

Section: Ba + Iba Combinations Resulted In Higher Multiplication Of Amentioning

confidence: 99%

“…BA induced the sprouting in all treatments only in subculture 1 with a peak between 0.1 and 0.5 mg.L -1 , while in the other subcultures its effect was more pronounced only at 0.1 mg.L -1 . The importance of auxin and cytokinin balance has been reported in regulating the apical dominance as well as in a number of morphogenetic events such as shoot formation and branching (Li and Bangerth, 2003;Werner et al, 2003;Nakagawa et al, 2005). Another factor that may influence the morphogenetic events during in vitro culture is a possible interaction between the endogenous concentrations of plant growth regulators and those present in the culture medium (Pinto et al, 1994;Mercier et al, 2003).…”

Section: Ba + Iba Combinations Resulted In Higher Multiplication Of Amentioning

confidence: 99%

Micropropagation of Alibertia edulis Rich

Silva

Pereira

Silveira

2008

Braz. arch. biol. technol.

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Overexpression of a petunia zinc‐finger gene alters cytokinin metabolism and plant forms

Cited by 56 publications

References 44 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

The BUD2 mutation affects plant architecture through altering cytokinin and auxin responses in Arabidopsis

Micropropagation of Alibertia edulis Rich

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