Stanga, John , Boonsirichai, Kanokporn , Sedbrook, John , Masson, Patrick H. .
A Mutation in Translocon of Outer Membrane of Chloroplasts 132 (Toc132) Enhances Gravitropic Defect of altered response to gravity 1 (arg1).
Arabidopsis roots perceive gravity and reorient their growth accordingly. The root cap is necessary for a full response to gravity. Starch-dense amyloplasts within the columella cells of the root cap are important for gravitropism, as starchless mutants (pgm1) display an attenuated response to gravistimulation. However, our understanding of the molecular events controlling this behavior is incomplete. The altered response to gravity 1 (arg1) mutant is known to be involved with the early phases of gravity signal transduction. arg1 responds slowly to gravistimulation, and is in a genetically distinct pathway from pgm1. arg1 seeds were mutagenized with EMS to identify new mutants that would enhance the gravitropic defect of arg1 and therefore be members of a separate genetic pathway. The roots of one such mutant, mar2, have no obvious defects, yet grow in random directions only when arg1 is present. Unlike pgm1 mutants, amyloplasts in the mar2 arg1 double mutant appear normal and sediment like wild-type amyloplasts. mar2 plants possess a mutation in the Translocon of Outer Membrane of Chloroplast 132 (TOC132) gene, At2g16640, that results in premature termination of translation. Overexpression of TOC132 rescues the random growth phenotype of arg1mar2 roots. In addition to green tissues, Toc132 is expressed in tissues that lack chloroplasts, such as the columella cells of the root cap. Toc132 is thought to act as a receptor for either preproteins destined for translocation into a plastid or proteins targeted to the outer membrane of plastids. Its exact contribution to the determination of root growth direction remains the subject of ongoing endeavors.
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1 - University of Wisconsin-Madison, Genetics, 3302 Genetics/Biotech, 425-G Henry Mall, Madison, WI, 53706, United States
2 - Center for Atomic Research for Peace Purposes-Bangkok, Thailand
3 - Illinois State University, Biological Sciences
4 - University of Wisconsin-Madison, Genetics
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM