Root hairs are highly elongated tubular extensions of root epidermal cells with a plethora of physiological functions, particularly in establishing the root–rhizosphere interface. Anisotropic expansion of root hairs is generally thought to be exclusively mediated by tip growth—a highly controlled apically localized secretion of cell wall material-enriched vesicles that drives the extension of the apical dome. Here we show that tip growth is not the only mode of root hair elongation. We identified events of substantial shank-localized cell wall expansion along the polar growth axis of Arabidopsis root hairs using morphometric analysis with quantum dots. These regions expanded after in vivo immunolocalization using cell wall-directed antibodies and appeared as distinct bands that were devoid of cell wall labelling. Application of a novel click chemistry-enabled galactose analogue for pulse chase and real-time imaging allowed us to label xyloglucan, a major root hair glycan, and demonstrate its de novo deposition and enzymatic remodelling in these shank regions. Our data reveal a previously unknown aspect of root hair growth in which both tip- and shank-localized dynamic cell wall deposition and remodelling contribute to root hair elongation.
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This work was supported by the Villum Foundation grants (00023089; ‘TIPorNOT’) to K.H. and (00017489; ‘Instant Architect’) to J.M. S.S. acknowledges the financial support of the Research Foundation Flanders (FWO post-doc fellowship), and K.V. was supported by a University Antwerpen Grant (BOF-DOCPRO4). S. C. Fry (University of Edinburgh, UK) is kindly acknowledged for supplying [3H]XXXGol. Imaging data were in part acquired at the Center for Advanced Bioimaging (CAB) Denmark, University of Copenhagen.
The authors declare no competing interests.
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Supplementary Figs. 1–10, legends for Supplementary Movies 1–8.
Time lapse (50 min) of root hair labelled with q-dots (1.5 µg ml−1). Confocal fluorescence images (Z-projections; red) were merged with corresponding images collected in a separate channel. Q-dots sprinkled to the root hair shank do not move, suggesting no shank expansion. Scale bar, 10 µm.
Time lapse (78 min) of root hair labelled with q-dots (1.5 µg ml−1). Confocal fluorescence (red) and corresponding bright-field images are shown. The nucleus migrating into the growing root hair is highlighted with an asterisk. Root hair shank-located q-dots move towards the polar growth direction, tracking shank expansion. Corresponds to data shown in Fig. 1b. Scale bar, 10 µm.
Time lapse (49 min) of root hair labelled with q-dots (1.5 µg ml−1). Arrows follow two q-dots that move towards the growth direction. Pale arrows highlight the original locations of the moving q-dots. The left movie shows a magnification of the marked area in the left movie. Corresponds to data shown in Fig. 1c. Scale bar, 10 µm.
Time lapse (30 min) of root hair with Golgi apparatus marker (Wave18, Got1P homologue). Scale bar, 10 µm.
Time lapse (60 min) of root hair with ER marker (Wave7Y, YFP-NIP1;1). Scale bar, 10 µm.
Time lapse (78 min) of root hair ‘click labelled’ with aGal-DBCO-Cy5 (for concentrations of aGal and dye, see Fig. 4b). Confocal fluorescence images (red) are shown. Note emerging unlabelled bands in two different root hairs. Corresponds to data shown in Fig. 4b. Scale bar, 10 µm.
Time lapse (140 min) of root hairs from xyloglucan-deficient xxt1/2/5 mutant plant labelled with q-dots (1.5 µg ml−1). Scale bar, 10 µm.
Time lapse (40 min) of root hair growing in presence of 30 mM C4. Corresponds to data in Fig. 4d. Scale bar, 10 µm.
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Herburger, K., Schoenaers, S., Vissenberg, K. et al. Shank-localized cell wall growth contributes to Arabidopsis root hair elongation. Nat. Plants 8, 1222–1232 (2022). https://doi.org/10.1038/s41477-022-01259-y
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