Date of Award


Degree Name

Master of Science


Biological Sciences

First Advisor

Dr. Yan Lu

Second Advisor

Dr. Terrell L. Hodge

Third Advisor

Dr. Pamela E. Hoppe

Fourth Advisor

Dr. Brian C. Tripp


Aspatate kinase, homoserine dehydrogenase, arabidopsis thaliana, nannochloropsis, oceanica, amino acids

Access Setting

Masters Thesis-Open Access


In plants, essential amino acid biosynthesis predominantly or exclusively occurs in the plastid. The plastid in the heterokont alga Nannochloropsis oceanica is surrounded by four membranes, which add great complexity to intracellular trafficking and communication. N. oceanica genes in essential amino acid biosynthesis were functionally annotated. The biosynthesis pathways resemble the pathways in Arabidopsis thaliana, but the gene content seems to be simpler in N. oceanica.

In addition, two A. thaliana mutants with loss-of-function mutations in the aspartate kinase-homoserine dehydrogenase 2 (AK-HSDH2) gene were characterized. These ak-hsdh2 mutants demonstrate unexpected accumulation of aspartate-derived amino acids (ADAAs), particularly threonine, in leaves. Microarray analysis supports that other ADAA biosynthesis-related genes are not up- or down-regulated in the mutants. The AK and HSDH activities were measured in mutant and wild-type plants. AK-HSDH2 appears to be an important contributor to the overall HSDH activity, but not a major contributor to the overall AK activity. The changes in the amino acid content over a range of leaf developmental stages were examined using mutants with loss-of-function mutations in AK-HSDH2 and/or another AK or HSDH gene. The accumulation of ADAAs in the mutants is a dynamic process.