Actin-dependant trichome cell morphogenesis
The leaf trichome cell in Arabidopsis arises as a small bump on the epidermis and enlarges into a tubular form. It may now initiate branch points to form ultimately two to four-branched cell or may remain unbranched. Branch extension is relatively rapid [1].
Mutants having defects in branch expansion have been described in Arabidopsis and because of the random shapes of the trichomes, have been placed into a distorted class [1].
The DISTORTED group of genes includes ALIEN, CROOKED, DISTORTED1, DISTORTED2, GNARLED, KLUNKER, SPIRRIG and WURM. Treatment of wild-type Arabidopsis plants with drugs that interfere with the actin cytoskeleton phenocopies dis trichomes [2, 3, 4].
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In addition visualization of the F-actin in some of the distorted mutants confirmed that they had an aberrant actin cytoskeletal organization [2, 3, 4].
Actin involvement in trichome morphogenesis is now established throufgh the identification of CROOKED [5, 6], DISTORTED1 [6, 7, 8], DISTORTED2 [9, 10], GNARLED [11, 12, 13], KLUNKER [13] and WURM [6,7, 8] genes from Arabidopsis. CRK, DIS1, DIS2 and WRM encode different subunits of a highly conserved modulator of the actin cytoskeleton, the ARP2/3 complex. GRL and KLK encode NAP-125 and PIR-121 homologs, respectively and might be components of the upstream ARP2/3 complex regulating machinery [11-14].
References
1. Hulskamp M. Plant trichomes: a model for cell differentiation. Nat Rev Mol Cell Biol. 2004 Jun;5(6):471-80.
2. Mathur J, Spielhofer P, Kost B, Chua N. The actin cytoskeleton is required to elaborate and maintain spatial patterning during trichome cell morphogenesis in Arabidopsis thaliana. Development. 1999 Dec;126(24):5559-68.
3. Szymanski DB, Marks MD, Wick SM. Organized F-actin is essential for normal trichome morphogenesis in Arabidopsis. Plant Cell. 1999 Dec;11(12):2331-47.
4. Schwab B, Mathur J, Saedler R, Schwarz H, Frey B, Scheidegger C, Hulskamp M. Regulation of cell expansion by the DISTORTED genes in Arabidopsis thaliana: actin controls the spatial organization of microtubules. Mol Genet Genomics. 2003 Jun;269(3):350-60. Epub 2003 Apr 11.
5. Mathur J, Mathur N, Kirik V, Kernebeck B, Srinivas BP, Hulskamp M. Arabidopsis CROOKED encodes for the smallest subunit of the ARP2/3 complex and controls cell shape by region specific fine F-actin formation.Development. 2003 Jul;130(14):3137-46.
6. Li S, Blanchoin L, Yang Z, Lord EM. The putative Arabidopsis arp2/3 complex controls leaf cell morphogenesis. Plant Physiol. 2003 Aug;132(4):2034-44.
7. Mathur J, Mathur N, Kernebeck B, Hulskamp M. Mutations in actin-related proteins 2 and 3 affect cell shape development in Arabidopsis. Plant Cell. 2003 Jul;15(7):1632-45.
8. Le J, El-Assal Sel-D, Basu D, Saad ME, Szymanski DB. Requirements for Arabidopsis ATARP2 and ATARP3 during epidermal development. Curr Biol. 2003 Aug 5;13(15):1341-7.
9. El-Din El-Assal S, Le J, Basu D, Mallery EL, Szymanski DB. DISTORTED2 encodes an ARPC2 subunit of the putative Arabidopsis ARP2/3 complex. Plant J. 2004 May;38(3):526-38.
10. Saedler R, Mathur N, Srinivas BP, Kernebeck B, Hulskamp M, Mathur J. Actin control over microtubules suggested by DISTORTED2 encoding the Arabidopsis ARPC2 subunit homolog. Plant Cell Physiol. 2004 Jul;45(7):813-22.
11. El-Assal Sel-D, Le J, Basu D, Mallery EL, Szymanski DB. Arabidopsis GNARLED Encodes a NAP125 Homolog that Positively Regulates ARP2/3. Curr Biol. 2004 Aug 10;14(15):1405-9.
12. Deeks MJ, Kaloriti D, Davies B, Malho R, Hussey PJ. Arabidopsis NAP1 Is Essential for Arp2/3-Dependent Trichome Morphogenesis. Curr Biol. 2004 Aug 10;14(15):1410-4.
13. Brembu T, Winge P, Seem M, Bones AM. NAPP and PIRP Encode Subunits of a Putative Wave Regulatory Protein Complex. Involved in Plant Cell Morphogenesis. Plant Cell. 2004 Aug 17.
14. Basu D., El-Assal S.E., Le J. Mallery E.L., Szymanski D.B. Interchangeable functions of Arabidopsis PIROGI and the human WAVE complex subunit SRA1 during leaf epidermal development. Development. 2004 131, 4345-4355.
