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Date of Award
Doctor of Philosophy (PhD)
Protein prenylation is one of the posttranslational lipid modifications that facilitate protein-membrane association and protein-protein interactions. Three types of heterodimeric protein prenyltransferases, protein farnesyltransferase (PFT), protein geranylgeranyltransferase-I (PGGT-I), and protein geranylgeranyltransferase-II or Rab geranylgeranyltransferase (Rab-GGT), are present in all eukaryotes. In Arabidopsis there are two putative genes encoding Rab-GGT α subunits, termed RGTA1 and RGTA2, and two putative genes encoding β subunits, RGTB1 and RGTB2, but little is known about Arabidopsis Rab-GGT activity. In this dissertation, I demonstrate that four different heterodimers can be formed between RGTA1, RGTA2, RGTB1, and RGTB2, but only RGTA1-RGTB1 and RGTA1-RGTB2 exhibit bona fide Rab-GGT activity, and they are biochemically redundant in vitro. Arabidopsis Rab-GGTs may have a preference for prenylation of C-terminal cysteines in particular positions. Arabidopsis Rab-GGTs can prenylate not only a great variety of Rab GTPases in a Rab escort protein (REP)-dependent manner, but, unlike Rab-GGT in yeast and mammals, can also prenylate select non-Rab GTPases in an REP-independent manner. PROTEIN PRENYLTRANSFERASE α-SUBUNIT-LIKE (PPAL), a newly-identified Arabidopsis gene encoding a protein similar to the known protein prenyltransferase α subunits, may also act as a Rab-GGT subunit. PPAL physically interacts with RGTB1. ppal mutants show slowed growth, defective male fertility, and hypersensitivity to abscisic acid (ABA). The most striking phenotype, however, is severe sugar hypersensitivity, which likely results from impaired sugar homeostasis. Together my work reveals the functional role of Rab-GGT subunits, helps explain the weak phenotype of many Arabidopsis prenyltransferase mutants, and uncovers a role for a newly-identified putative Rab-GGT subunit in sugar response and sugar-ABA signaling crosstalk.
Chair and Committee
Ram Dixit, Kenneth Olsen, Sona Pandey, Hani Zaher
Shi, Wan, "Functional Characterization of Putative Rab Geranylgeranyltransferase Subunits in Arabidopsis thaliana" (2015). Arts & Sciences Electronic Theses and Dissertations. 681.
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