Journal Article

Role of the <i>SPIRAL1</i> Gene Family in Anisotropic Growth of <i>Arabidopsis thaliana</i>

Keiji Nakajima, Tomomi Kawamura and Takashi Hashimoto

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 4, pages 513-522
Published in print April 2006 | ISSN: 0032-0781
Published online April 2006 | e-ISSN: 1471-9053 | DOI:
Role of the SPIRAL1 Gene Family in Anisotropic Growth of Arabidopsis thaliana

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Arabidopsis spiral1 (spr1) mutants show a right-handed helical growth phenotype in roots and etiolated hypocotyls due to impaired directional growth of rapidly expanding cells. SPR1 encodes a small protein with as yet unknown biochemical functions, though its localization to cortical microtubules (MTs) suggests that SPR1 maintains directional cell expansion by regulating cortical MT functions. The Arabidopsis genome contains five SPR1-LIKE (SP1L) genes that share high sequence identity in N- and C-terminal regions. Overexpression of SP1Ls rescued the helical growth phenotype of spr1, indicating that SPR1 and SP1L proteins share the same biochemical functions. Expression analyses revealed that SPR1 and SP1L genes are transcribed in partially overlapping tissues. A combination of spr1 and sp1l mutations resulted in randomly oriented cortical MT arrays and isotropic expansion of epidermal cells. These observations suggest that SPR1 and SP1Ls act redundantly in maintaining the cortical MT organization essential for anisotropic cell growth, and that the helical growth phenotype of spr1 results from a partially compromised state of cortical MTs. Additionally, inflorescence stems of spr1 sp1l multiple mutants showed a right-handed tendril-like twining growth, indicating that a directional winding response may be conferred to the non-directional nutational movement by modulating the expression of SPR1 homologs.

Keywords: Arabidopsis thaliana; Cell expansion; Cytoskeleton; Microtubule; SPIRAL1; CaMV, cauliflower mosaic virus; dpg, days post-germination; EST, expressed sequence tag; GFP, green fluorescent protein; GUS, β-glucuronidase; MT, microtubule; SP1L, SPIRAL1-LIKE; SPR1, SPIRAL1; RT–PCR, reverse transcription–PCR

Journal Article.  5754 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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