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Auxin influx carriers control vascular patterning and xylem differentiation in Arabidopsis thaliana.

Fàbregas N, Formosa-Jordan P, Confraria A, Siligato R, Alonso JM, Swarup R, Bennett MJ, Mähönen AP, Caño-Delgado AI, Ibañes M - PLoS Genet. (2015)

Bottom Line: Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation.In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation.Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, Centre for Research in Agricultural Genomics (CRAG) CSIC-IRTA-UAB-UB, Barcelona, Spain.

ABSTRACT
Auxin is an essential hormone for plant growth and development. Auxin influx carriers AUX1/LAX transport auxin into the cell, while auxin efflux carriers PIN pump it out of the cell. It is well established that efflux carriers play an important role in the shoot vascular patterning, yet the contribution of influx carriers to the shoot vasculature remains unknown. Here, we combined theoretical and experimental approaches to decipher the role of auxin influx carriers in the patterning and differentiation of vascular tissues in the Arabidopsis inflorescence stem. Our theoretical analysis predicts that influx carriers facilitate periodic patterning and modulate the periodicity of auxin maxima. In agreement, we observed fewer and more spaced vascular bundles in quadruple mutants plants of the auxin influx carriers aux1lax1lax2lax3. Furthermore, we show AUX1/LAX carriers promote xylem differentiation in both the shoot and the root tissues. Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation. In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation. Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.

No MeSH data available.


Vascular pattern and xylem differentiation phenotypes in long day and short day conditions for influx aux1lax1lax2lax3 and efflux pin1pin2 mutants.Basal shoot cross section of aux1lax1lax2lax3 (A, D), WT (B, E) and pin1pin2 (C, F) plants grown in long day conditions (A-C) and in short day conditions (D-E). WT and the aux1lax1lax2lax3 plants grown in long day conditions showed no statistical significant differences in number of VBs, total cell number, nor average vascular unit size (S11 Fig, n = 18 for WT, n = 15 for aux1lax1lax2lax3). Scale bars: 500μm. VB detail of aux1lax1lax2lax3 (G, J), WT (H, K) and pin1pin2 (I, L) shoot inflorescence stem grown in long day conditions (G-I) and in short day conditions (J-L). Light blue dots indicate undifferentiated cell layers in procambium tissue between phloem and xylem differentiated cells. First differentiated xylem cell is indicated by white arrow. White brackets highlight the interfascicular fiber cells (if). Black brackets highlight the xylem cells (xy). Scale bars: 200 μm. Frequency distribution of the number of undifferentiated cell layers in long day conditions for the three genotypes is shown in S11 Fig.
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pgen.1005183.g004: Vascular pattern and xylem differentiation phenotypes in long day and short day conditions for influx aux1lax1lax2lax3 and efflux pin1pin2 mutants.Basal shoot cross section of aux1lax1lax2lax3 (A, D), WT (B, E) and pin1pin2 (C, F) plants grown in long day conditions (A-C) and in short day conditions (D-E). WT and the aux1lax1lax2lax3 plants grown in long day conditions showed no statistical significant differences in number of VBs, total cell number, nor average vascular unit size (S11 Fig, n = 18 for WT, n = 15 for aux1lax1lax2lax3). Scale bars: 500μm. VB detail of aux1lax1lax2lax3 (G, J), WT (H, K) and pin1pin2 (I, L) shoot inflorescence stem grown in long day conditions (G-I) and in short day conditions (J-L). Light blue dots indicate undifferentiated cell layers in procambium tissue between phloem and xylem differentiated cells. First differentiated xylem cell is indicated by white arrow. White brackets highlight the interfascicular fiber cells (if). Black brackets highlight the xylem cells (xy). Scale bars: 200 μm. Frequency distribution of the number of undifferentiated cell layers in long day conditions for the three genotypes is shown in S11 Fig.

Mentions: Next, the vascular phenotype in the shoot stem of influx mutants grown in long day was analyzed, since in these light conditions no apparent vascular bundle number phenotype is seen in aux1lax1lax2lax3 mutants (Figs 4A, 4B, 4D and 4E and S11), in agreement with the phyllotactic phenotypes described previously for these mutants in these conditions [31]. We found that the vascular differentiation was impaired in the quadruple mutants, albeit the phenotype was milder than in short day conditions (Figs 4G, 4H, 4J and 4K and S11). These results support that the role of AUX1/LAX in vascular differentiation is more prevalent than their role on modulating the vascular bundle number.


Auxin influx carriers control vascular patterning and xylem differentiation in Arabidopsis thaliana.

Fàbregas N, Formosa-Jordan P, Confraria A, Siligato R, Alonso JM, Swarup R, Bennett MJ, Mähönen AP, Caño-Delgado AI, Ibañes M - PLoS Genet. (2015)

Vascular pattern and xylem differentiation phenotypes in long day and short day conditions for influx aux1lax1lax2lax3 and efflux pin1pin2 mutants.Basal shoot cross section of aux1lax1lax2lax3 (A, D), WT (B, E) and pin1pin2 (C, F) plants grown in long day conditions (A-C) and in short day conditions (D-E). WT and the aux1lax1lax2lax3 plants grown in long day conditions showed no statistical significant differences in number of VBs, total cell number, nor average vascular unit size (S11 Fig, n = 18 for WT, n = 15 for aux1lax1lax2lax3). Scale bars: 500μm. VB detail of aux1lax1lax2lax3 (G, J), WT (H, K) and pin1pin2 (I, L) shoot inflorescence stem grown in long day conditions (G-I) and in short day conditions (J-L). Light blue dots indicate undifferentiated cell layers in procambium tissue between phloem and xylem differentiated cells. First differentiated xylem cell is indicated by white arrow. White brackets highlight the interfascicular fiber cells (if). Black brackets highlight the xylem cells (xy). Scale bars: 200 μm. Frequency distribution of the number of undifferentiated cell layers in long day conditions for the three genotypes is shown in S11 Fig.
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pgen.1005183.g004: Vascular pattern and xylem differentiation phenotypes in long day and short day conditions for influx aux1lax1lax2lax3 and efflux pin1pin2 mutants.Basal shoot cross section of aux1lax1lax2lax3 (A, D), WT (B, E) and pin1pin2 (C, F) plants grown in long day conditions (A-C) and in short day conditions (D-E). WT and the aux1lax1lax2lax3 plants grown in long day conditions showed no statistical significant differences in number of VBs, total cell number, nor average vascular unit size (S11 Fig, n = 18 for WT, n = 15 for aux1lax1lax2lax3). Scale bars: 500μm. VB detail of aux1lax1lax2lax3 (G, J), WT (H, K) and pin1pin2 (I, L) shoot inflorescence stem grown in long day conditions (G-I) and in short day conditions (J-L). Light blue dots indicate undifferentiated cell layers in procambium tissue between phloem and xylem differentiated cells. First differentiated xylem cell is indicated by white arrow. White brackets highlight the interfascicular fiber cells (if). Black brackets highlight the xylem cells (xy). Scale bars: 200 μm. Frequency distribution of the number of undifferentiated cell layers in long day conditions for the three genotypes is shown in S11 Fig.
Mentions: Next, the vascular phenotype in the shoot stem of influx mutants grown in long day was analyzed, since in these light conditions no apparent vascular bundle number phenotype is seen in aux1lax1lax2lax3 mutants (Figs 4A, 4B, 4D and 4E and S11), in agreement with the phyllotactic phenotypes described previously for these mutants in these conditions [31]. We found that the vascular differentiation was impaired in the quadruple mutants, albeit the phenotype was milder than in short day conditions (Figs 4G, 4H, 4J and 4K and S11). These results support that the role of AUX1/LAX in vascular differentiation is more prevalent than their role on modulating the vascular bundle number.

Bottom Line: Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation.In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation.Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, Centre for Research in Agricultural Genomics (CRAG) CSIC-IRTA-UAB-UB, Barcelona, Spain.

ABSTRACT
Auxin is an essential hormone for plant growth and development. Auxin influx carriers AUX1/LAX transport auxin into the cell, while auxin efflux carriers PIN pump it out of the cell. It is well established that efflux carriers play an important role in the shoot vascular patterning, yet the contribution of influx carriers to the shoot vasculature remains unknown. Here, we combined theoretical and experimental approaches to decipher the role of auxin influx carriers in the patterning and differentiation of vascular tissues in the Arabidopsis inflorescence stem. Our theoretical analysis predicts that influx carriers facilitate periodic patterning and modulate the periodicity of auxin maxima. In agreement, we observed fewer and more spaced vascular bundles in quadruple mutants plants of the auxin influx carriers aux1lax1lax2lax3. Furthermore, we show AUX1/LAX carriers promote xylem differentiation in both the shoot and the root tissues. Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation. In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation. Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.

No MeSH data available.