The auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon
esculentum Mill.) has a pleiotropic phenotype including a lack of lateral roots and
reduced gravitropic response, apical dominance, vascular development, and fruit
growth. The dgt mutation reduces the auxin sensitivity of only a subset of auxin
responses while levels, metabolism, and transport of auxin appear normal,
suggesting that the Dgt gene encodes a component in an auxin-signaling pathway.
This dissertation reports isolation and characterization of the Dgt gene.
Delineation of three microsyntenic regions in the Arabidopsis genome containing
genes homeologous to genetic markers near the Dgt gene allowed isolation of
additional ESTs from the corresponding tomato region, significantly reducing the
mapping distance to the dgt locus. Further analysis determined that the Dgt gene
encodes a cyclophilin (LeCYP1), a previously unidentified component of auxin
signaling. Each known dgt allele contains a unique mutation in the coding
sequence of LeCyp1. In addition, the wild-type Dgt gene can complement dgt
mutant plants. Cyclophilins characteristically have peptidylprolyl cis-trans
isomerase (PPIase) activity, but it is unclear whether that activity is necessary for
all of their biological functions. Each allelic dgt mutation reduces or nullifies PPIase
activity of LeCYP1 fusion proteins in vitro. Immunoblot analysis indicates that all
three dgt mutations are null mutations. Phylogenetic comparisons of tomato and
Arabidopsis cytosolic-type cyclophilins could not identify any single Arabidopsis
member as orthologous to LeCYP1/DGT. Five T-DNA insertion mutants were
analyzed to determine if mutations in Arabidopsis cytosolic-type cyclophilins
phenocopy the pleiotropic dgt phenotype. Overall seedling growth and morphology
appear normal in the mutants, however, their gravitropic response is slow. The
lack of exact phenocopy may be due to the redundant nature of Cyp genes in
Arabidopsis, which has over twice as many Cyp genes as tomato. In tomato, the
cyclophilin inhibitor cyclosporin A (CsA) inhibits auxin-induced adventitious root
initiation and expression of two early auxin response genes, LeIAA10 and 11, that
are also affected by the dgt mutation. Taken together, these results suggest that
the cyclophilin encoded by the Dgt gene plays an important role in auxin signal
transduction. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31803 |
| Date | 15 July 2003 |
| Creators | Oh, KwangChul |
| Contributors | Lomax, Terri L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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