UBC Theses and Dissertations
Non-canonical enzymes involved in cuticular wax biosynthesis : weaving the coat of Arabidopsis and cereal shoots Sun, Yulin
Plant cuticles play important roles in plant development, fertility, and adaptation. The cuticular waxes directly facing the environment are made mainly from derivatives of very-long-chain (VLC) aliphatics. Previous studies on cuticular waxes clarified the biosynthesis of ubiquitous wax components based on the model plant Arabidopsis thaliana. However, the biosynthesis and chemical structures of numerous uncommon wax components from different plant species are still unclear. In my Ph.D. studies, I focused on wax components from both Arabidopsis thaliana and Poaceae crop species to identify new enzymes involved in plant cuticular wax biosynthesis and further characterize their biochemical functions. In chapter 2, I investigated alkane biosynthesis in bread wheat. The linkage of alkane content and transcriptome data revealed a candidate gene, TaCER1-1A. The phenotype of corresponding nullisomic-tetrasomic substitution wheat lines and heterologous expression of TaCER1-1A in rice and Arabidopsis confirmed its function in alkane synthesis. In chapter 3, the products associated with β-diketones in barley were profiled. New diketone homologs, the 2-alkanol ester profile and the ¹³C isotope abundance of different wax components indicated the unique biosynthesis pathway to β-diketones. The biochemical functions of the core enzymes on this pathway, DIKETONE METABOLISM HYDROLASE (DMH) and DIKETONE METABOLISM POLYKETIDE SYNTHASE (DMP), were investigated. In vivo and in vitro assays showed the direct condensation between 3-ketoacid and fatty acyl-CoA catalyzed by DMP, thus revealing the unique character of DMP as a PKS family member and revised the model of the β-diketone synthesis pathway in barley. In chapter 4, VLC alkenes from Arabidopsis young leaves were analyzed. Different from other plant species, alkenes ranging from C₃₃ to C₃₉ with predominance of 7- and 9- isomers were found in Arabidopsis. An acyl-CoA desaturase family member, ADS4.2, was shown to influence alkene formation. ADS4.2 was strongly expressed in young rosette leaves, especially in trichomes, and yeast expression revealed that this enzyme had ω-7 regio-specificity with high preference for acyl-CoAs longer than C₃₂. Wax-synthesis-deficient mutants were used to put the alkene-forming pathway in context with the wax synthesis. The results show that Arabidopsis produces characteristic alkenes through a unique elongation-desaturation pathway with the participation of ADS4.2.
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