Philosophiae Doctor - PhD / Self-incompatibility (SI) is a major mechanism that prevents inbreeding in
ow-ering plants, which was identi ed in Rosaceae, Solanaceae and Scrophulariace.
In these families, SI is gametophytic and retains inter-speci c genetic variations
by out-crossing promotion. Self-incompatibility is genetically controlled by an S-
locus where both male (pollen) and female (pistil) S-determinants are encoded.
The female determinant (SRNase) has been extensively studied, whereas its male
counterpart (SLF/SFB) has only recently been characterized as a pollen-expressed
protein, which encodes for an F-box domain. However, the exact mechanism of in-
teraction between SLF/SFB and SRNase is still largely unclear in Rosaceae. This
study takes a closer look at the mechanism of self-incompatibility to gain a clearer
understanding of the ligand-receptor binding mechanism of SI using molecular
evolutionary analysis, structure prediction and binding speci city characteriza-
tion, the outcome of which, will translate into a guideline for future studies. The
major aims of this study were to derive an evolutionary pattern for GSI in Rosaceae
subfamilies and to further assess the collaborative non-self recognition in Malus
domestica Borkh.. The evolutionary analysis suggests a di erence in the evolution-
ary pattern of Prunoideae and Maloideae S-genes, hence proposing a di erence in
their GSI systems. Furthermore, sites responsible for this divergence are identi ed
as critical amino acids in GSI function. To maintain GSI it is expected that the
S-genes must be linked and co-evolve as a genetic unit. The results of this study
show that these genes have co-existed, while SRNase have experienced a higher
rate of evolution compared to SLF, thus rejecting the co-evolution of these genes
in Maloideae. Furthermore, positively selected sites of S-locus pistil and pollen
genes were identi ed that are likely to be responsible for speci city determination.
Di erent numbers of these sites are found for both S-genes, while SRNase holds
a larger number of positively selected sites. Additionally a model of speci city
is introduced that supports the collaborative non-self recognition in Malus GSI,
while critical sites responsible for such speci city are proposed and mapped to the
predicted ancestral tertiary structure of SRNase and SLF/SFB. The identi cation
of regions determining pollen pistil speci city as well as proposing a Collaborative
Non-self Recognition model for Malus domestica Borkh. provide greater in-sight into how pollen-pistil communication system works in Maloideae (Rosaceae
subfamily).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uwc/oai:etd.uwc.ac.za:11394/3948 |
| Date | January 2012 |
| Creators | Ashkani, Jahanshah |
| Contributors | Rees, D.J.G., Ndimba, B. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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