Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Mark A. Bernards

Abstract

Soybean (Glycine max [L.] Merr.) is a globally cultivated crop that is important to the sustainability of many industries. However, like all plants, optimal cultivation of soybean is threatened by detrimental environmental factors. For example, high yield of soybean is threatened by soil-borne pathogens like Phytophthora sojae. Resistance against P. sojae was previously positively correlated with aliphatic suberin deposition in soybean. As such, a deeper understanding of the biosynthesis of suberin may assist in engineering a resistant form of soybean, based on enhanced suberin content. In soybean, the ω-OH fatty acid monomers are predominant and most strongly correlated with resistance. These ω-OH fatty acids are synthesized by CYP86As (a subfamily of fatty-acid ω-hydroxylase (FAωH) enzymes). In soybean, two putative FAωH genes, CYP86A37 and CYP86A38 are expressed in roots. Using a hairy root model system, RNAi knockdown lines for CYP86A37 and CYP86A38 were generated. Expression of CYP86A37 and CYP86A38 confirmed knockdown of the two genes, and downstream changes in suberin deposition were quantified using GC/MS. Expression of CYP86A37 and CYP86A38 was also compared across cultivars (Williams, Conrad, and OX760-6) and a developmental axis, and related to aliphatic suberin deposition. Expression of these two genes positively correlated only with the ω-hydroxylated suberin monomers, particularly 18-hydroxy-oleic acid. Unexpectantly, gene expression and amount of suberin deposition did not relate to known disease resistance in the three cultivars. Overall, my data indicates that CYP86A37 and CYP86A38 likely display fatty-acid ω-hydroxylase function and are therefore likely involved in suberin biosynthesis. As the expression of these two genes impacts the composition of the suberin polymer, it will be important to further explore these genes including developmental regulation to gain insight into the factors contributing to the suberin phenotype.

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