Current Biology
Volume 23, Issue 10, 20 May 2013, Pages 895-900
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Impaired Cellulose Synthase Guidance Leads to Stem Torsion and Twists Phyllotactic Patterns in Arabidopsis

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Highlights

  • Without cellulose deposition guidance, chiral torsion occurs in a thick plant stem

  • Stem torsion leads to a postmeristematic bimodal phyllotaxis

  • Phyllotaxis in the meristem does not depend on cellulose synthase guidance by CSI1

  • Apparent alternate phyllotaxis may be related to stem torsion in nature

Summary

The parallel alignment of stiff cellulose microfibrils in plant-cell walls mediates anisotropic growth [1, 2]. This is largely controlled by cortical microtubules, which drive the insertion [3, 4] and trajectory of the cellulose synthase (CESA) complex at the plasma membrane [5, 6, 7]. The CESA interactive protein 1 (CSI1) acts as a physical linker between CESA and cortical microtubules [8, 9, 10]. Here we show that the inflorescence stems of csi1 mutants exhibit subtle right-handed torsion. Because cellulose deposition is largely uncoupled from cortical microtubules in csi1, we hypothesize that strictly transverse deposition of microfibrils in the wild-type is replaced by a helical orientation of uniform handedness in the mutant and that the helical microfibril alignment generates torsion. Interestingly, both elastic and viscous models for an expanding cell predict that a net helical orientation of microfibrils gives rise to a torque [11, 12]. We indeed observed tilted microfibrils in csi1 cells, and the torsion was almost absent in a csi1 prc1 background with impaired cellulose synthesis. In addition, the stem torsion led to a novel bimodal and robust phyllotactic pattern in the csi1 mutant, illustrating how growth perturbations can replace one robust mathematical pattern with a different, equally robust pattern.

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These authors contributed equally to this work