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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.


LR spacing is altered in cytokinin-deficient plants. (A-I) No proximal LRP and LRs were observed in wild type (A, B) whereas LRP and LRs in close proximity were observed in acr4 (C, D) and 35S:CKX1 (E-I). Red asterisks indicate borders of LRP or emerged LRs. (J) Proportion of LRP separated by different PC number in 11-d-old wild-type, acr4, and cytokinin-deficient 35S:CKX1 plants. n (number of roots analysed) = 15. (K) Expression of the CycB1;1:GUS and DR5:GUS marker genes indicates division of neighbouring PCs in 35S:CKX1 plants but not in wild-type plants and a normal auxin pattern in aberrantly positioned LRP and LRs. Black arrowheads indicate LRP. Bar size in (A-I) and (K) is 50 µM. Significance of differences in (J) was analysed by two-tailed Student’s t-test. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars indicate SEM (this figure is available in colour at JXB online).
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Figure 1: LR spacing is altered in cytokinin-deficient plants. (A-I) No proximal LRP and LRs were observed in wild type (A, B) whereas LRP and LRs in close proximity were observed in acr4 (C, D) and 35S:CKX1 (E-I). Red asterisks indicate borders of LRP or emerged LRs. (J) Proportion of LRP separated by different PC number in 11-d-old wild-type, acr4, and cytokinin-deficient 35S:CKX1 plants. n (number of roots analysed) = 15. (K) Expression of the CycB1;1:GUS and DR5:GUS marker genes indicates division of neighbouring PCs in 35S:CKX1 plants but not in wild-type plants and a normal auxin pattern in aberrantly positioned LRP and LRs. Black arrowheads indicate LRP. Bar size in (A-I) and (K) is 50 µM. Significance of differences in (J) was analysed by two-tailed Student’s t-test. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars indicate SEM (this figure is available in colour at JXB online).

Mentions: First, LR spacing in cytokinin-deficient 35S:CKX1 transgenic Arabidopsis seedlings (Werner et al., 2003) was compared with acr4 mutant seedlings known to have a LR positioning defect (De Smet et al., 2008) and wild-type seedlings under the same growth conditions. In wild-type roots almost no LRP or emerged LRs initiated from immediately adjacent or opposite sites (Fig. 1A,B). Among 373 LRI events in 15 wild-type roots, only five LRP (1.3±0.6%) were located in immediate proximity (Fig. 1J). In contrast, in acr4 mutant plants LRP initiated from adjacent or opposite sites (Fig. 1C,D), which is consistent with previous results (De Smet et al., 2008). In total, 39 LRP out of 348 LRI events (11.0±1.9%) were formed from these aberrant positions (Fig. 1J). Similarly, 76 LRP out of 811 LRI events (9.1±0.9%) were located immediately adjacent or opposite to each other in 35S:CKX1 plants (Fig. 1J). There was phenotypic variability in the defective spacing pattern. In some instances stretches of several PCs showed cell division activity (Fig. 1E) and closely spaced LRP were formed either on the longitudinal axis (Fig. 1F) or on the opposite side of the axis (Fig. 1G). Closely spaced LRP mostly belonged to the same developmental stage or differed by just one stage (according to Malamy and Benfey, 1997), indicating that they were induced at a similar time (Fig. 1F,G). Albeit less frequent, cytokinin-deficient plants also sometimes formed clusters of closely spaced LRP of different growth stages (Fig. 1H). Rarely, several closely spaced LRP emerged and appeared as clustered LRs (Fig. 1I). However, the proportion of emerged neighbouring LRs was low, suggesting that most of the LRP at aberrant positions arrest during development and do not contribute much to the overall root architecture. Notably, the primary roots of acr4 mutants were only about 15% shorter than those of wild type (data not shown) and those of 35S:CKX1 transgenic plants were even longer (Werner et al., 2003), indicating that the shorter distance between LRP is not correlated with the length of the primary root.


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

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

LR spacing is altered in cytokinin-deficient plants. (A-I) No proximal LRP and LRs were observed in wild type (A, B) whereas LRP and LRs in close proximity were observed in acr4 (C, D) and 35S:CKX1 (E-I). Red asterisks indicate borders of LRP or emerged LRs. (J) Proportion of LRP separated by different PC number in 11-d-old wild-type, acr4, and cytokinin-deficient 35S:CKX1 plants. n (number of roots analysed) = 15. (K) Expression of the CycB1;1:GUS and DR5:GUS marker genes indicates division of neighbouring PCs in 35S:CKX1 plants but not in wild-type plants and a normal auxin pattern in aberrantly positioned LRP and LRs. Black arrowheads indicate LRP. Bar size in (A-I) and (K) is 50 µM. Significance of differences in (J) was analysed by two-tailed Student’s t-test. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars indicate SEM (this figure is available in colour at JXB online).
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Figure 1: LR spacing is altered in cytokinin-deficient plants. (A-I) No proximal LRP and LRs were observed in wild type (A, B) whereas LRP and LRs in close proximity were observed in acr4 (C, D) and 35S:CKX1 (E-I). Red asterisks indicate borders of LRP or emerged LRs. (J) Proportion of LRP separated by different PC number in 11-d-old wild-type, acr4, and cytokinin-deficient 35S:CKX1 plants. n (number of roots analysed) = 15. (K) Expression of the CycB1;1:GUS and DR5:GUS marker genes indicates division of neighbouring PCs in 35S:CKX1 plants but not in wild-type plants and a normal auxin pattern in aberrantly positioned LRP and LRs. Black arrowheads indicate LRP. Bar size in (A-I) and (K) is 50 µM. Significance of differences in (J) was analysed by two-tailed Student’s t-test. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars indicate SEM (this figure is available in colour at JXB online).
Mentions: First, LR spacing in cytokinin-deficient 35S:CKX1 transgenic Arabidopsis seedlings (Werner et al., 2003) was compared with acr4 mutant seedlings known to have a LR positioning defect (De Smet et al., 2008) and wild-type seedlings under the same growth conditions. In wild-type roots almost no LRP or emerged LRs initiated from immediately adjacent or opposite sites (Fig. 1A,B). Among 373 LRI events in 15 wild-type roots, only five LRP (1.3±0.6%) were located in immediate proximity (Fig. 1J). In contrast, in acr4 mutant plants LRP initiated from adjacent or opposite sites (Fig. 1C,D), which is consistent with previous results (De Smet et al., 2008). In total, 39 LRP out of 348 LRI events (11.0±1.9%) were formed from these aberrant positions (Fig. 1J). Similarly, 76 LRP out of 811 LRI events (9.1±0.9%) were located immediately adjacent or opposite to each other in 35S:CKX1 plants (Fig. 1J). There was phenotypic variability in the defective spacing pattern. In some instances stretches of several PCs showed cell division activity (Fig. 1E) and closely spaced LRP were formed either on the longitudinal axis (Fig. 1F) or on the opposite side of the axis (Fig. 1G). Closely spaced LRP mostly belonged to the same developmental stage or differed by just one stage (according to Malamy and Benfey, 1997), indicating that they were induced at a similar time (Fig. 1F,G). Albeit less frequent, cytokinin-deficient plants also sometimes formed clusters of closely spaced LRP of different growth stages (Fig. 1H). Rarely, several closely spaced LRP emerged and appeared as clustered LRs (Fig. 1I). However, the proportion of emerged neighbouring LRs was low, suggesting that most of the LRP at aberrant positions arrest during development and do not contribute much to the overall root architecture. Notably, the primary roots of acr4 mutants were only about 15% shorter than those of wild type (data not shown) and those of 35S:CKX1 transgenic plants were even longer (Werner et al., 2003), indicating that the shorter distance between LRP is not correlated with the length of the primary root.

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.