Abstract
Many plants, including agronomically important species, exhibit hybridization barriers. Previous interploidy hybridization studies show that increased copies of epigenetically imprinted genes in paternal germlines delay cellularization during seed development which causes endosperm failure and eventual F1 seed lethality. However, allelic variation occurs in Arabidopsis thaliana; so that most ecotypes will also produce a proportion of larger, viable seeds in inter-ecotype interploidy crosses. Therefore, genes that determine variable strength in post-zygotic hybridization barriers are potential tools to enhance seed size and seed yield in crop plants.The Columbia-0 (Col-0) ecotype exerts an exceptionally strong asymmetrical post-zygotic barrier when used in paternal chromosome copy excess in 2x X 4x crosses in such a way that most seeds die. Certain ecotypes, such as Tsushumi (Tsu-0), when used as maternal pollen recipients, are able to strongly suppress Col 4x killing. As yet, neither severe Col 4x killing nor the maternal rescue effected by Tsu-0 have been characterized. Clarification of the mechanism causing Col 4x killing and the means by which it is mitigated, would lead to a deeper understanding of how seed size is controlled.
QTL analyses were used to map the genomic regions responsible for Col 4x killing and Tsu-0 mediated maternal rescue. A population of [Tsu-0xCol-0] recombinant inbred lines (RILs) was used. In one QTL analysis study to uncover loci responsible for Col 4x killing, tetraploidized [Tsu-0xCol-0] RILs were used as pollen parents and crossed with Col-0. Two additive loci on chromosome 1 and on chromosome 5 were identified. Backcrossing and genotyping indicated that the QTL peak at the bottom of chromosome 5 was primarily associated with Col 4x killing.
Comparative genomic studies of this region under this QTL peak on chromosome 5 using tetraploid ecotypes associated with the potential identification of the geographical location of the Col-0 ecotype and that exhibit Col 4x killing, produced genomic regions of interest that could contain candidate genes responsible for Col 4x killing. These studies showed that Li-5 4x produces identical endosperm failure indistinguishable for Col 4x killing, suggesting this ecotype and Col-0 have a common origin in the Limburg region of Germany.
In another QTL analysis study to identify loci responsible for Tsu-0 mediated maternal rescue, [Tsu-0XCol-0] RILs were used as maternal parents and crossed with Col 4x in 2x X 4x crosses. A dominant effect QTL was identified at the top of chromosome 5.
A potential candidate gene for Col 4x killing, At5g64030, an uncharacterized pectin methyltransferase affecting mucilage persistence of the endosperm and a likely candidate gene for Tsu-0 mediated maternal rescue, TTG1, a key regulator of mucilage biosynthesis, may interact to produce larger, viable seeds and prevent F1 seed lethality.
| Date of Award | 17 Nov 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | James Doughty (Supervisor), Rod Scott (Supervisor) & Baoxiu Qi (Supervisor) |