Identification and characterization of plant lipid droplet-associated proteins
Kumulative Dissertation
Datum der mündl. Prüfung:2023-06-29
Erschienen:2024-02-23
Betreuer:Prof. Dr. Till Ischebeck
Gutachter:Prof. Dr. Till Ischebeck
Gutachter:Prof. Dr. Andrea Polle
Dateien
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Zusammenfassung
Englisch
The molecular study of plant lipid droplets, first described over a century ago, has garnered attention since the identification of oleosins in the 1980s’. In recent years, considerable progress has been achieved in identifying and characterizing plant lipid droplet proteome constituents. However, most of our understanding originates from investigations conducted on oil seeds, seedlings, mesocarp, pollen, and leaves, with a disproportionate focus on angiosperms. Lipid droplets are present across all domains of life, although the proteins and their composition identified thus far exhibit significant diversity, even within the same species’ tissues. Therefore, a high degree of specialization and functional versatility can be expected. Indeed, lipid droplets have been associated with numerous biological processes, encompassing lipid metabolism and remodeling, energy storage, signaling, and the production of defense compounds. They may also enhance resilience to abiotic stress. Lately, lipid droplets and a subset of their proteins have been proposed to be a remnant of an ancient desiccation tolerance mechanism that persists in angiosperm seeds and pollen. The advantage obtained by early land plants through this mechanism may have been pivotal for the great success of plant terrestrialization. In this thesis, we applied a bottom-up label-free proteomic approach on desiccation tolerant and oil-rich tubers of yellow nutsedge and compared it against the same species’ leaves and roots, as well as desiccation sensitive and oil-depleted tubers of the closest related species, purple nutsedge. The acquired data unveiled a proteomic fingerprint consisting of antioxidants, heat shock proteins, and late embryogenesis abundant proteins resembling desiccation-tolerant seeds’ composition. Furthermore, our findings strongly indicate that seed-type lipid droplet proteins oleosins, caleosins, steroleosins, and a seed lipid droplet protein play central roles in the seed-like desiccation tolerance program. The putative co-option of those features in tubers may be achieved through transcription factors ABSCISIC ACID INSENSITIVE3, WRINKLED1, and LEAFY COTYLEDON1 regulation. Applying a similar approach to germinating spores of Physcomitrium patens and comparing them to vegetative gametophytes, most of these desiccation tolerance-mediating traits reappear, further supporting the hypothesis that they existed prior to the emergence of seeds. It further sheds light on the LD proteome composition of a bryophyte spore. In another proteomic study, we described lipid droplet protein composition for the first time in the subterranean tissue of Arabidopsis thaliana roots. As a result, we were able to identify 12 novel proteins localized to the lipid droplets, in addition to 31 previously described. Their assigned functions indicate diverse metabolic roles, involvement in developmental processes, and responses to stress, which highlights the nature of lipid droplets as active organelles in vegetative tissues. Protein characterization is a time-consuming process, and for several identified LD proteins, characterization has not yet been conducted. To initially characterize the lipid dropletassociated methyltransferase (LIME) protein family, a range of techniques was employed, including in silico phylogeny, cell biological approaches, phenotype evaluation, and biochemical analyses. This approach provided initial insights into a highly conserved protein family with an unique and complex lipid droplet targeting mechanism. It is putatively the evolutionary origin of complex alkaloid-producing methyltransferases found in opium poppy and other species, but likely has a distinct function. Overall, this work identifies new plant lipid droplet proteins and contributes to our understanding of the roles of these in desiccation tolerance. It further gives first insights into the LIME protein family. Therefore, it will serve as a foundation for further research.
Keywords: lipid droplets; Arabidopsis thaliana; Physcomitrium patens; proteomics; Cyperus esculentus; lipid droplet-associated methyltransferase; spores; desiccation tolerance; tubers