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First published online 8 October 2003
doi: 10.1242/dev.00659

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AXR3 and SHY2 interact to regulate root hair development

¹ Department of Biology, University of York, Box 373, York YO10 5YW, UK
² School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK

View larger version (77K): [in a new window]   Fig. 1. Root hair phenotypes of 5-day old seedlings: (A) Columbia ecotype, (B) axr3-1, (C) axr3-10, (D) Landsberg erecta (Ler) ecotype, (E) shy2-2 and (F) shy2-31. Scale bar: 0.5 mm.

View larger version (14K): [in a new window]   Fig. 2. Quantitative analysis of root hair phenotypes. (A) Mean number of root hairs per mm root. At least 50 measurements were taken for each genotype, visible hairs were counted in a 1mm section of mature root, and only those observed from above were counted. (B) Mean epidermal cell length (mm). One hundred cells, both atrichoblasts and trichoblasts, were measured for each genotype, from at least 10 different plants. (C) Number of root hairs per one cell length. The measurements for number of hairs per mm were multiplied by the corresponding epidermal cell length, to give the mean number of hairs per unit cell length. (D) Mean length of root hairs. Fifty hairs were measured, from at least 10 different plants, for each genotype. Only hairs in mature sections of the root were measured. (E) Mean length of root hairs grown on medium with no phosphate. Fifteen hairs were measured, from at least 3 plants. All measurements were made on 5-day-old plants. Bars represent the standard errors of the means.

View larger version (7K): [in a new window]   Fig. 3. Distance from the root tip to the first initiating root hair (mm). The values shown are the means for 50 5-day old plants of each genotype. Bars represent standard errors of the means.

View larger version (10K): [in a new window]   Fig. 4. shy2-2 and shy2-31 root hair outgrowth determined by time-lapse analysis. (A) Mean root hair growth rate calculated from images taken at 10-minute intervals after the transition to tip growth. Growth rate is therefore presented as mean increase in length per 10-minute interval. (B) Mean increase in trichoblast cell length following root hair initiation. (C) Time taken for a hair to reach final length from the initiation bump stage. The values shown are the means of at least 5 hairs for A and C and 10 trichoblasts for B. Bars represent standard errors of the means.

View larger version (13K): [in a new window]   Fig. 5. Mean root hair length at four time points: 4, 8, 12 and 24 hours after the shy2-6 or axr3-1 transgene induction from the heat shock promoter (HS). The same transgenic lines without heat shock were used as controls (Con). The mean length of 10 root hairs from at least three plants, at each time point, is shown and bars represent the standard errors of the means.

View larger version (129K): [in a new window]   Fig. 6. Root phenotypes induced by transient expression of axr3-1 or shy2-6 transgenes from the heat shock promoter. (A) Heat shocked wild-type Columbia root, showing no effect of the heat shock (administered at the time when the part of the root indicated by the arrow was entering the root hair initiation zone). (B) HS:axr3-1 root following a 2-hour HS (arrow), showing blocked hair growth and root agravitropism. (C) Close up of HS:axr3-1 root treated as in B showing the transition back to hair growth: a few shorter hairs appear before normal hair growth resumes. (D) Transient induction of axr3-1 transcription from the heat shock promoter in the shy2-2 genetic background. Following induction, all hairs arrest at their current stage of development, and initiation is blocked. (E) Close up of HS:axr3-1, shy2-2 root treated as in D showing the transition back to hair growth: an area of the root becomes gnarled and produces depolarised root hairs. Scale bar: 0.5 mm.

View larger version (70K): [in a new window]   Fig. 7. Whole-mount in situ analysis of AXR3 and SHY2 expression. (A) Antisense AXR3 after 4 hours' development of the signal. Signal is strong throughout the elongation zone and fading into the zone of differentiation (indicated by arrow). (B) Sense AXR3 probe after 4 hours' development of the signal. (C) Antisense SHY2 after 4.5 hours' development of the signal. Dark staining throughout the tip extends into the zone of differentiation (indicated by arrow). (D) Sense SHY2, after 4.5 hours' development of the signal. Slight background signal is visible in the epidermis. Scale bar: 0.1 mm.

View larger version (12K): [in a new window]   Fig. 8. Model to explain the root hair phenotypes of the genotypes studied in this work. Red and blue arrows indicate sites of SHY2 and AXR3 protein accumulation, respectively.