Many plants exhibit post-zygotic barriers to hybridisation and failure of crosses is frequently associated with abnormal endosperm development. The “triploid block” is one such example that results from intraspecific crosses between diploid and tetraploid plants. Here, paternal excess usually leads to severe endosperm over-proliferation, failure of cellularisation and consequent arrest of embryo development. Most ecotypes of Arabidopsis thaliana tolerate 2xX4x crosses which result in enlarged viable seeds, however the Columbia (Col-0) ecotype exhibits a classic triploid block. Previous work suggested that some genes involved in regulation of the flavonoid biosynthesis pathway (FBP) could act as maternal modifiers of the Col4x-mediated triploid block, re-imposing a normal (balanced) developmental programme on the endosperm. The FBP operates in a specialised maternal layer of the seed coat, the endothelium, which lies adjacent to the endosperm.This study set out to understand the role of the FBP and its products in the regulation of seed development following 2xX4x crosses. To this end, a collection of FBP mutants was assembled to test their effect on alleviating the triploid block. Both light and confocal microscopy was utilised to assess the effects of FBP mutations on seed development and biochemical analysis (ESI–LC–MS/MS) was used to determine if particular products of the FBP were significant. In addition, a potential link between the hormone auxin and the FBP was investigated in seeds by utilising FBP mutants carrying the fluorescent auxin “response” reporter DR5rev::GFP. This work revealed that many (though not all) mutations of the FBP lead to alleviation of the triploid block and that, in particular, perturbations to the pathway that result in a reduction of proanthocyanidins or affect normal vacuolar biogenesis in the endothelium are associated with ‘rescue’ from Col4x-induced seed lethality. Preliminary evidence is presented that does suggest a potential link between auxin transport and products of the FBP though how this may operate is unclear.
|Date of Award||22 Jun 2016|
|Sponsors||Umm Al-Qura University|
|Supervisor||James Doughty (Supervisor) & Roderick Scott (Supervisor)|