Unravelling the molecular bases of carotenoid biosynthesis in maize
Berman Quintana, Judit
Universitat de Lleida. Departament de Producció Vegetal i Ciència Forestal
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My research program focused on the elucidation of the mechanisms of carotenoid accumulation in maize (Zea mays). I amplified a putative carotenoid ε-hydroxylase, named CYP97C19, from the yellow maize variety B73. Metabolic profiling of the carotenoid pathway in Arabidopsis lut1 mutant (lacking lutein) overexpressing maize CYP97C19 confirmed the accumulation of lutein in transgenic lines at the expense of zeinoxanthin. This allowed me to conclude that maize CY P97C19 is a functional ε-hydroxylase. In a separate experiment, I characterized two transgenic lines overexpressing the Arabidopsis Orange gene (AtOR). Both lines exhibited an increase in carotenoid content without any concomitant upregulation of endogenous carotenogenic gene expression. The highest carotenoid accumulating line was crossed with different transgenic lines with diverse carotenoid profiles. In cases in which the original transgenic parent that was crossed with the AtOr line accumulated low levels of total carotenoids, resulting hybrids exhibited a substantial increase of total carotenoid content without any changes in the qualitative carotenoid composition. No changes at the metabolite and transcript profiles were observed in the hybrids when the carotenoid content in the original parents used to cross with the AtOr line was high. Results from these experiments suggest that one of the functions of the Orange gene in maize endosperm is to generate a metabolic sink for carotenoids. Results from experiments in which carotenoid β-hydroxylase (BCH1 and BCH2) was silenced in genotypes able to accumulate high lutein and high zeaxanthin levels indicated that these genes are determinans of β-carotene and zeaxanthin accumulation. I also investigated the interactions between the carotenoid and starch biosynthetic pathways as they share common precursors. I analyzed total starch content in four transgenic maize lines: one line overexpressing AtOR (L1) and three lines expressing different carotenogenic gene combinations (L2, L3 and L4, expressing Zmpsy1; Zmpsy1; PacrtI; ParacrtW; and Zmpsy1; ParacrtW and Gllycb, respectively). In transgenic lines with a high carotenoid content total starch content was lower by approximately 8%. I established that this effect was not due to downregulation of starch-related biosynthetic genes, which suggests that reduction in starch levels might be due to an alternative mechanism. A transgenic line (HC) overexpressing Zmpsy1 and PacrtI was crossed with different inbred lines belonging to well-known heterotic groups in order to obtain high-yielding hybrids accumulating carotenoids. I assessed the performance of the hybrids (agronomic and ear morphologic traits) in two different environments in one growing season. Results indicated that field performance of high carotenoid maize hybrids was similar or on occasion superior to commercial hybrids commonly grown in the area.
European research projects
- Tesis Doctorals 
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