Investigating the mechanism of self-incompatibility in Papaver rhoeas and functional transfer of Papaver S-determinants to Arabidopsis thaliana

Flowering plants have evolved complex genetic mechanisms of self-incompatibility (SI) to overcome the problem of self-fertilization. SI is a cell-cell recognition system where the interaction of genetically linked pollen and pistil S-determinants prevents self-fertilization. In Papaver rhoeas, the pistil S-determinant is PrsS, a secreted protein of around 15 kDa. The pollen determinant, PrpS, encodes a novel transmembrane protein of around 20 kDa. Upon the interaction of incompatible PrsS and PrpS variants, the SI response is triggered, activating a signalling network. Rapid increases in cytosolic free calcium ([Ca$^{2+}$]$_i$) are followed by changes to the actin cytoskeleton and activation of a DEVDases, resulting in programmed cell death (PCD). Within this thesis, three inter-related studies are described. Initially, we investigated the role of the ubiquitin-proteasomal system during SI in Papaver, the second study focused on the PrpS protein. Thirdly, we also created transgenic Arabidopsis thaliana lines expressing PrpS and PrsS, in order to investigate if the Papaver SI system might be functionally transferable to other plant species. We have demonstrated that PrpS binds the PrsS in an S-specific manner, while the functional analysis “in vitro” revealed that PrpS expressed in A.thaliana is functional and that just PrpS and PrsS are sufficient for a fully functional SI response in A.thaliana pollen

Exploring ComQXPA quorum-sensing diversity and biocontrol potential of Bacillus spp. isolates from tomato rhizoplane

Bacillus subtilis is a widespread and diverse bacterium t exhibits a remarkable intraspecific diversity of the ComQXPA quorum-sensing (QS) system. This manifests in the existence of distinct communication groups (pherotypes) that can efficiently communicate within a group, but not between groups. Similar QS diversity was also found in other bacterial species, and its ecological and evolutionary meaning is still being explored. Here we further address the ComQXPA QS diversity among isolates from the tomato rhizoplane, a natural habitat of B. subtilis, where these bacteria likely exist in their vegetative form. Because this QS system regulates production of anti-pathogenic and biofilm-inducing substances such as surfactins, knowledge on cell–cell communication of this bacterium within rhizoplane is also important from the biocontrol perspective. We confirm the presence of pherotype diversity within B. subtilis strains isolated from a rhizoplane of a single plant. We also show that B. subtilis rhizoplane isolates show a remarkable diversity of surfactin production and potential plant growth promoting traits. Finally, we discover that effects of surfactin deletion on biofilm formation can be strain specific and unexpected in the light of current knowledge on its role it this process