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Auxin transport through non-hair cells sustains root-hair development


The plant hormone auxin controls root epidermal cell development in a concentration-dependent manner1,2,3. Root hairs are produced on a subset of epidermal cells as they increase in distance from the root tip. Auxin is required for their initiation4,5,6,7 and continued growth8,9,10,11, but little is known about its distribution in this region of the root. Contrary to the expectation that hair cells might require active auxin influx to ensure auxin supply, we did not detect the auxin-influx transporter AUX1 in root-hair cells. A high level of AUX1 expression was detected in adjacent non-hair cell files. Non-hair cells were necessary to achieve wild-type root-hair length, although an auxin response was not required in these cells. Three-dimensional modelling of auxin flow in the root tip suggests that AUX1-dependent transport through non-hair cells maintains an auxin supply to developing hair cells as they increase in distance from the root tip, and sustains root-hair outgrowth. Experimental data support the hypothesis that instead of moving uniformly though the epidermal cell layer3,12, auxin is mainly transported through canals that extend longitudinally into the tissue.

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Figure 1: AUX1 and PIN2 expression in hair and non-hair epidermal cells.
Figure 2: Basipetal AUX1-mediated auxin transport is required for auxin-dependent root-hair growth.
Figure 3: Non-hair cells are essential for root-hair development, but an auxin response is not required in non-hair cells.
Figure 4: Expression of AUX1 in non-hair cells affects the supply of auxin to hair cells in the differentiation zone of the root.
Figure 5: DR5::GFP expression and root-hair growth dynamics support the model auxin distribution.

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We thank J. Schiefelbein for sharing material before publication, and Alan Champneys and Robert Payne for insightful discussions. A.R.J. was supported by a BBSRC studentship awarded to C.M.L. and C.S.G., and by the Lady Emily Smyth Agricultural Research Station; K.K. was supported by a BBSRC Case Award to H.M.O.L. and C.S.G.; M.B., R.S. and E.K. received support from the Centre for Plant Integrative Biology, which is a BBSRC/EPSRC Centre for Integrative Systems Biology.

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A.R.J., H.M.O.L. and C.S.G conceived the project; A.R.J., C.M.L. and C.S.G. designed, performed and analysed the experiments, apart from the work with AXR3; K.K. and H.M.O.L. designed, performed and analysed the AXR3 experiments; E.K. produced the computer model; R.S. and M.B. provided valuable experimental materials and advice; A.R.J. and E.K. wrote the paper. All authors contributed to the interpretation of results and edited the manuscript.

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Correspondence to Claire S. Grierson.

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Jones, A., Kramer, E., Knox, K. et al. Auxin transport through non-hair cells sustains root-hair development. Nat Cell Biol 11, 78–84 (2009).

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