AtIPT3 is a Key Determinant of Nitrate-Dependent Cytokinin Biosynthesis in Arabidopsis

Abstract

;We analyzed the spatial expression pattern of Arabidopsis thaliana adenosine phosphates-isopentenyltransferase genes (AtIPT1, AtIPT3 to AtIPT8) and the effect of inorganic nitrogen sources on their regulation. In mature plants, the AtIPTs were differentially expressed in various tissues including the roots, leaves, stems, flowers and siliques. In transgenic seedlings expressing a gene for green fluorescent protein (GFP) driven by the AtIPT promoters, AtIPT1::GFP was predominantly expressed in the vascular stele of the roots, AtIPT3::GFP was in the phloem companion cells, AtIPT5::GFP was in the lateral root primordium and pericycle, and AtIPT7::GFP was in both the vascular stele and the phloem companion cells of the roots. In a longterm treatment, the accumulation level of AtIPT5 transcript was correlated with the concentrations of NO 3 -and NH 4 + in the growth medium. However, under nitrogenlimited conditions, AtIPT3 expression was rapidly induced by NO 3 -in the seedlings accompanying the accumulation of cytokinins, whereas AtIPT5 expression was little affected. The NO 3 --dependent accumulation of both the AtIPT3 transcript and the cytokinins was markedly reduced in a Ds transposon-insertion mutant of AtIPT3. These results suggest that nitrogen availability differentially regulates expression of AtIPT3 and AtIPT5, and that AtIPT3 is a key determinant of cytokinin biosynthesis in response to rapid changes in the availability of NO 3 -.

Functional Characterization of the GATA Transcription Factors GNC and CGA1 Reveals Their Key Role in Chloroplast Development, Growth, and Division in Arabidopsis

“…GNC was first identified based on its transcriptional induction by nitrate (Wang et al, 2003;Price et al, 2004;Scheible et al, 2004;Bi et al, 2005), which in retrospect provided a first link with cytokinin because of the well-established role for nitrogen in regulating cytokinin biosynthesis and translocation (Samuelson and Larsson, 1993;Takei et al, 2001Takei et al, , 2004Miyawaki et al, 2004). CGA1 expression is strongly affected by exogenous cytokinin (Brenner et al, 2005;Kiba et al, 2005;Rashotte et al, 2006;Naito et al, 2007), and our quantitative data now demonstrate that both CGA1 and GNC are misregulated in arr1 arr12 mutants.…”

Arabidopsis ABCG14 protein controls the acropetal translocation of root-synthesized cytokinins

“…These data suggest that the roots, particularly the root pericycle and phloem company ARTICLE cells, are the main sites of tZ production and that tZR might act as an acropetal signal. In contrast, iP-and cZ-types are the main cytokinins in phloem sap, where they might function as basipetal or systemic signals 10,33,34 .…”

“…Several cytokinin biosynthetic genes are found mainly expressed in the root, for instance, AtIPT1 and AtIPT7 are primarily expressed in the vascular stele of the elongation zone and/or root phloem companion cells, indicating that these sites are major sources of root-derived cytokinins 33 . Moreover, the xylem sap of several plant species predominantly contains tZ-type cytokinins, especially tZ riboside (tZR) 10,34 .…”

“…They also play key roles in regulating reproductive development and sink strength 37,38 ; thus, they are among the most important target hormones for improving crop yields. Furthermore, they are pivotal signals in communicating nitrogen availability from roots to shoots via the xylem vessels 10,33 . However, the regulation of their distribution in plants is poorly understood.…”

Chitinase-Like Protein CTL1 Plays a Role in Altering Root System Architecture in Response to Multiple Environmental Conditions

“…Long-distance signals mediating the shoot response to nitrate perception in roots may also involve cytokinins. It is possible that the reduction in cytokinins observed during N deficiency (Takei et al, 2004) relieves a general inhibition of root growth by this hormone and that an increase in auxin stimulates cell division and LR development. In the latter case, auxin reprograms cells overlaying LR primordia to facilitate organ emergence, and genes encoding several Arabidopsis cell wall remodeling enzymes have been reported to be expressed in these cells (Péret et al, 2009, and refs.…”