The GAP in Fruit Development: Determining the Role of RanGAP in Arabidopsis Fruit Development
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Date
2014-05
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The Ohio State University
Abstract
RanGAP is the activating protein for the small GTPase Ran, and is known to be
involved in nucleocytoplasmic transport and mitotic cell division across
kingdoms. Arabidopsis has two RanGAP proteins, RanGAP1 and RanGAP2, which
share 63% amino acid homology. Both proteins contain two functional domains: a
localization domain known as the WPP domain, which contains a conserved tryptophanproline-
proline motif necessary for interaction with localization binding partners, and a
GTPase activation (GAP) domain, which is responsible for Ran binding and activation.
Double null mutants in the genes encoding RanGAP1 and RanGAP2 are lethal at an early
stage of development. However, a homozygous mutant combining the RanGAP1 null
allele and RanGAP2 knockdown allele, called short silique knockdown (SILK), exhibits a
reduced fruit (silique) length phenotype. What role RanGAP plays in fruit development,
however, is unknown. In order to determine its function, constructs containing
wildtype RanGAP1 or mutant RanGAP1 with one or both functional domains mutated
were inserted into SILK mutant plants. Their phenotypes were quantified by measuring
fruit length and seed number to determine if the RanGAP1 transgene had rescued the
short-fruit phenotype. RanGAP1 transgenes with mutations in the GAP domain did not
rescue the SILK phenotype whereas mutants that maintained this function did, regardless
of localization. These results indicate that it is the GAP function of RanGAP that is
important in fruit development. Seed count, however, varied greatly among individual
lines with the same transgene, indicating that seed development may depend on the
location of the RanGAP1 insertion into the genome. Further analysis of silique cell types
indicate that the length phenotype may be due to defects in the differentiation of the cells
of the fruit itself. This work highlights the intersection between cell biological processes
and developmental events, and shows the relevance of intracellular events to the
understanding of whole-plant processes.
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Keywords
Arabidopsis, Fruit, Plant Biology, RanGAP, Nucleocytoplasmic Transport, Development