ROP GTPases are crucial regulators of pollen tube growth. The Rop GTPase family in maize consists
of nine known rop genes, ropl-rop9. A subset of these genes (rop2, rop8, and rop9) are expressed in
pollen. The rop2 and rop9 genes are a highly conserved duplicate gene pair of ancient origin. The
rop2/rop9 duplicate gene pair displays differential expression in mature and germinated pollen,
suggesting different roles for the genes in the process of male gametophyte development. To explore
ROP2 function in maize, five Mutator transposon insertions in the rop2 gene were isolated (rop2::Mu
alleles). I showed that three of the rop2::Mu alleles displayed reduced transmission through the male
and were associated with reduced levels of ROP2-mRNA. Interestingly, the rop2::Mu male-specific
transmission defect was apparent only when wild-type pollen was also present, an indication that the
mutation reduces the competitive ability of the rop2 gametophytes. Dual pollination and pollen
mixing experiments indicated that this competitive disadvantage is expressed by the majority of the
mutant gametophytes, and that expression of the phenotype is associated with a delay in the ability to
accomplish fertilization. Using the waxy phenotypic marker (linked to rop2 via a reciprocal
translocation) to distinguish between rop2::Mu and wild-type pollen derived from heterozygous plants,
I demonstrated that the delay is associated with a defect in early progamic development (i.e,
germination and early pollen tube growth). The defect was detectable in vivo as early as 15 minutes
after pollination. However, quantitative measurements provided no indication that the rop2 mutation
affects pollen tube growth in the style. Finally, investigations focusing on the final stages of pollen
function raise the possibility that a defect in the very last stages (i.e. either pollen tube guidance
through the micropyle to the egg sac, or fertilization of the egg sac) may also contribute to the rop2
mutant delay. This work provides direct in vivo evidence confirming a role for Rop in male
gametophyte development, and is the first study to demonstrate a role for Rop in the early stages of
post-pollination gametophytic function. / Graduation date: 2005
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29912 |
| Date | 26 October 2004 |
| Creators | Carroll, Kirstin Arthur |
| Contributors | Fowler, John E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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