Abscission is a programmed cell separation process that allows plants to shed their organs. In Arabidopsis flowers, each outer organ has a set of differentiated abscission zone cells at its base, which allow the organs to detach after pollination. Previous studies have shown that the NEVERSHED (NEV) ADP-ribosylation factor-GTPase-activating protein regulates membrane trafficking and is required for organ abscission. A nev suppressor screen has revealed that mutations in CAST AWAY (CST), a receptor-like cytoplasmic kinase, are capable of rescuing abscission. Localization of CST to the plasma membrane is supported by N-myristoylation and the kinase activity of CST is required for its activity. Mutations in CST were found to rescue the trafficking defects of nev mutant flowers: in nev cst flowers the organization of the Golgi apparatus and location of the trans-Golgi network are restored, and the accumulation of extracellular vesicles between the plasma membrane and cell wall is significantly reduced. Organ abscission is known to be triggered via activation of the HAESA (HAE) and HAESA-LIKE2 (HSL2) receptor-like kinases. In addition to CST, two other receptor-like kinases, EVERSHED (EVR) and SOMATIC EMBRYOGENESIS DEFICIENT IN ABSCISSION, are known to inhibit organ abscission. Interaction studies of CST, HAE, and EVR using the bimolecular fluorescence complementation assay suggest that CST may directly and indirectly modulate cell separation by regulating the localization and/or activity of HAE/HSL2 and EVR.
Functional analysis of NEV and three other ARF-GAP genes has revealed that NEV and ARF-GAP DOMAIN6 (AGD6) redundantly control plant growth and reproduction. nev agd6 double mutants are very small compared to wild-type plants; those that survive long enough to flower do not produce seeds. Analysis of leaf cell size suggests that reduced cell expansion is at least partially responsible for the growth defects of nev agd6 plants. We have also found that the root meristems of nev agd6 mutants are smaller than those of wild-type, and that growth of the primary roots is significantly reduced. Our studies suggest that NEV- and AGD6-mediated membrane trafficking regulates the localization of cell signaling molecules involved in establishing or maintaining meristem size.
|Advisor:||Liljegren, Sarah J.|
|Commitee:||Ahmed, Shawn, Duncan, Mara, Goldstein, Bob, Reed, Jason|
|School:||The University of North Carolina at Chapel Hill|
|Department:||Genetics & Molecular Biology|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 73/01, Dissertation Abstracts International|
|Subjects:||Molecular biology, Plant biology|
|Keywords:||Abscission, Membrane trafficking, Plants, Receptor kinase signaling|
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