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Cytokinin as a positional cue regulating lateral root spacing in Arabidopsis.

Chang L, Ramireddy E, Schmülling T - J. Exp. Bot. (2015)

Bottom Line: Interestingly, mutation of CYP735A genes required for trans-zeatin biosynthesis caused strong defects in LR positioning, indicating an important role for this cytokinin metabolite in regulating LR spacing.Further it is shown that cytokinin and a known regulator of LR spacing, the receptor-like kinase ARABIDOPSIS CRINKLY4 (ACR4), operate in a non-hierarchical manner but might exert reciprocal control at the transcript level.Taken together, the results suggest that cytokinin acts as a paracrine hormonal signal in regulating root system architecture.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D- 14195 Berlin, Germany Present address: Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, College of Life Science, Hubei University, Wuhan 430062, China.

No MeSH data available.


Related in: MedlinePlus

Spatio-temporal expression of selected cytokinin synthesis genes during LR development. A developmental sequence of the expression pattern of promoters of cytokinin metabolism genes is shown from left to right starting with stage I LRP to emerged LR. The respective promoter is indicated in the upper left corner of each picture series. Three-day-old seedlings were stained with GUS reaction buffer for 1h and cleared. GFP expression was analysed in 5-d-old seedlings using a confocal laser scanning microscope. Part of the root staining pattern reporting expression of the cytokinin metabolism genes shown here have been published before (Werner et al., 2003; Takei et al., 2004b; Kuroha et al., 2009; Kiba et al., 2013). Scale bars is 50 μM (this figure is available in colour at JXB online).
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Figure 2: Spatio-temporal expression of selected cytokinin synthesis genes during LR development. A developmental sequence of the expression pattern of promoters of cytokinin metabolism genes is shown from left to right starting with stage I LRP to emerged LR. The respective promoter is indicated in the upper left corner of each picture series. Three-day-old seedlings were stained with GUS reaction buffer for 1h and cleared. GFP expression was analysed in 5-d-old seedlings using a confocal laser scanning microscope. Part of the root staining pattern reporting expression of the cytokinin metabolism genes shown here have been published before (Werner et al., 2003; Takei et al., 2004b; Kuroha et al., 2009; Kiba et al., 2013). Scale bars is 50 μM (this figure is available in colour at JXB online).

Mentions: The LR spacing phenotype of cytokinin-deficient plants suggests that the normally occuring inhibition of LRP formation in the vicinity of a LRP that has started to form is abolished. In order to study the spatial organization of the signal generation mediating this inhibition, expression patterns and functions of cytokinin synthesis genes were analysed. The expression of several cytokinin synthesis genes, both IPT and LOG genes, as well as of cytokinin-degrading CKX genes has been reported to occur during LR formation (Werner et al., 2003; Miyawaki et al., 2004; Takei et al., 2004b; Kuroha et al., 2009; Parizot et al., 2010; Kiba et al., 2013). The spatio-temporal expression pattern of these genes during different stages of LR formation was studied in more detail because it has been reported in most cases only for one or two stages. A particularly intriguing expression pattern was shown by the IPT5, LOG4, and CKX6 genes, which were switched on very early during formation of LRP in stage I similar to DR5:GUS (Figs 1K and 2; Supplementary Fig. S1). During further LRP development IPT5 and LOG4 were expressed in most cells until emergence. In the emerged LR the expression of IPT5 became confined to the root tip and LOG4 was strongly expressed in provascular tissue and the LR meristem (Fig. 2). In contrast, CKX6 expression was observed in the vasculature and only in stage I LRP but not in the following stages (Figure S1). The pIPT3:GFP and pIPT7:GFP reporter did not show activity during early LR development. IPT3 was expressed in the PCs and the basal stele of young LRs, IPT7:GFP expression was confined principally to the vascular stele of the primary root (Fig. 2). Expression of reporter genes for LOG3, CKX1 and CKX5 became only visible in the vasculature and at the basis of the emerged LR (Supplementary Fig. S1). Also for pCYP735A2:GUS, no expression was seen in the primordium itself but there was a variable pattern and strength of expression in PCs and vascular tissue on either side of the existing primordia (Fig. 2). The expression pattern of pCYP735A1:GUS could not be analysed because of its low expression level (Takei et al., 2004a; Kiba et al., 2013). The gene expression analysis showed a specific pattern of cytokinin synthesis gene expression and pointed to the IPT5 and LOG4 genes as being possibly particularly relevant in creating a source of cytokinin in the young primordia. Their expression could establish an inhibitory field preventing LRI in neighbouring cells.


Cytokinin as a positional cue regulating lateral root spacing in Arabidopsis.

Chang L, Ramireddy E, Schmülling T - J. Exp. Bot. (2015)

Spatio-temporal expression of selected cytokinin synthesis genes during LR development. A developmental sequence of the expression pattern of promoters of cytokinin metabolism genes is shown from left to right starting with stage I LRP to emerged LR. The respective promoter is indicated in the upper left corner of each picture series. Three-day-old seedlings were stained with GUS reaction buffer for 1h and cleared. GFP expression was analysed in 5-d-old seedlings using a confocal laser scanning microscope. Part of the root staining pattern reporting expression of the cytokinin metabolism genes shown here have been published before (Werner et al., 2003; Takei et al., 2004b; Kuroha et al., 2009; Kiba et al., 2013). Scale bars is 50 μM (this figure is available in colour at JXB online).
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Related In: Results  -  Collection

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Show All Figures
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Figure 2: Spatio-temporal expression of selected cytokinin synthesis genes during LR development. A developmental sequence of the expression pattern of promoters of cytokinin metabolism genes is shown from left to right starting with stage I LRP to emerged LR. The respective promoter is indicated in the upper left corner of each picture series. Three-day-old seedlings were stained with GUS reaction buffer for 1h and cleared. GFP expression was analysed in 5-d-old seedlings using a confocal laser scanning microscope. Part of the root staining pattern reporting expression of the cytokinin metabolism genes shown here have been published before (Werner et al., 2003; Takei et al., 2004b; Kuroha et al., 2009; Kiba et al., 2013). Scale bars is 50 μM (this figure is available in colour at JXB online).
Mentions: The LR spacing phenotype of cytokinin-deficient plants suggests that the normally occuring inhibition of LRP formation in the vicinity of a LRP that has started to form is abolished. In order to study the spatial organization of the signal generation mediating this inhibition, expression patterns and functions of cytokinin synthesis genes were analysed. The expression of several cytokinin synthesis genes, both IPT and LOG genes, as well as of cytokinin-degrading CKX genes has been reported to occur during LR formation (Werner et al., 2003; Miyawaki et al., 2004; Takei et al., 2004b; Kuroha et al., 2009; Parizot et al., 2010; Kiba et al., 2013). The spatio-temporal expression pattern of these genes during different stages of LR formation was studied in more detail because it has been reported in most cases only for one or two stages. A particularly intriguing expression pattern was shown by the IPT5, LOG4, and CKX6 genes, which were switched on very early during formation of LRP in stage I similar to DR5:GUS (Figs 1K and 2; Supplementary Fig. S1). During further LRP development IPT5 and LOG4 were expressed in most cells until emergence. In the emerged LR the expression of IPT5 became confined to the root tip and LOG4 was strongly expressed in provascular tissue and the LR meristem (Fig. 2). In contrast, CKX6 expression was observed in the vasculature and only in stage I LRP but not in the following stages (Figure S1). The pIPT3:GFP and pIPT7:GFP reporter did not show activity during early LR development. IPT3 was expressed in the PCs and the basal stele of young LRs, IPT7:GFP expression was confined principally to the vascular stele of the primary root (Fig. 2). Expression of reporter genes for LOG3, CKX1 and CKX5 became only visible in the vasculature and at the basis of the emerged LR (Supplementary Fig. S1). Also for pCYP735A2:GUS, no expression was seen in the primordium itself but there was a variable pattern and strength of expression in PCs and vascular tissue on either side of the existing primordia (Fig. 2). The expression pattern of pCYP735A1:GUS could not be analysed because of its low expression level (Takei et al., 2004a; Kiba et al., 2013). The gene expression analysis showed a specific pattern of cytokinin synthesis gene expression and pointed to the IPT5 and LOG4 genes as being possibly particularly relevant in creating a source of cytokinin in the young primordia. Their expression could establish an inhibitory field preventing LRI in neighbouring cells.

Bottom Line: Interestingly, mutation of CYP735A genes required for trans-zeatin biosynthesis caused strong defects in LR positioning, indicating an important role for this cytokinin metabolite in regulating LR spacing.Further it is shown that cytokinin and a known regulator of LR spacing, the receptor-like kinase ARABIDOPSIS CRINKLY4 (ACR4), operate in a non-hierarchical manner but might exert reciprocal control at the transcript level.Taken together, the results suggest that cytokinin acts as a paracrine hormonal signal in regulating root system architecture.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences (DCPS), Freie Universität Berlin, Albrecht-Thaer-Weg 6, D- 14195 Berlin, Germany Present address: Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, College of Life Science, Hubei University, Wuhan 430062, China.

No MeSH data available.


Related in: MedlinePlus