Plants produce an astonishing variety of secondary metabolites (SMs) which are thought to play vital roles in the fitness of plants through ecological interactions. The most characteristic features... Show morePlants produce an astonishing variety of secondary metabolites (SMs) which are thought to play vital roles in the fitness of plants through ecological interactions. The most characteristic features of SMs are their striking chemical diversity and inter- or intraspecific variation. Due to the large number, high structural diversity and multifunctionality of SMs, it is still an ongoing challenge to understand how this SM diversity comes about, and why such a large diversity is maintained in nature. In this thesis this question was studied using the pyrrolizidine alkaloids (PAs) of Jacobaea species as the study system from an evolutionary and biosynthetic perspective. PA variations were studied among and within Jacobaea species, and species-specific PA profiles were observed. In order to understand how PA diversity is related to species phylogeny, the evolutionary histories and phylogenetic signals of individual PAs were investigated under the phylogenetic context of Jacobaea species and no strong phylogenetic signals were found. To shed light on the mechanisms underlying PA diversity, a gene-to-metabolite approach targeting cytochrome P450 monooxygenases which play an important role in the evolution of chemical diversity was applied to study their involvement in PA biosynthesis and PA diversity. Show less
Quality of the rice grain is determined mainly by starch and protein contents of the endosperm. In this thesis, the analyses of four genes involved in the regulation of development of rice grain... Show moreQuality of the rice grain is determined mainly by starch and protein contents of the endosperm. In this thesis, the analyses of four genes involved in the regulation of development of rice grain and floret are presented. Two CCCH type zinc finger proteins, OsGZF1 and OsGZF2, were identified as novel transcription factors for GluB-1, one of the major seed-storage protein genes. Both of them exhibited negative effects on the GluB-1 promoter in transient expression assays. In a collection of rice mutants, two Tos17 transposon lines were identified showing open-staying florets and abnormal seed development. The mutant gene was identified as OsJAR1 and was shown to encode a jasmonic acid-amino acid synthetase. Next, we identified the potassium antiporter OsCHX14 as one of the downstream genes of OsJAR1. Yeast complementation assays confirmed that OsCHX14 is capable of effluxing K+ outside of cells. Its potential role in regulating of floret closure in rice was discussed. Show less
