Agronomy and Horticulture Department

 

Date of this Version

5-2012

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Agronomy, Under the Supervision of Professor Tom Clemente. Lincoln, Nebraska: May, 2012

Copyright (c) 2012 Hyunwoo Park

Abstract

The objectives of this study are: 1. To develop of soybean oil low in palmitic acid and elevated in stearic and oleic acids for margarine source. 2. To produce the high omega-3 fatty acid and astaxanthin in soybean seed as a feedstock for aquaculture. Over expression of mangosteen stearoyl-ACP thioesterase gene increased stearic acid content up to 10% to 15%. The identified elevated stearic acid events were crossed with our high oleic acid/low palmitic acid event. Average stearic and oleic acid content ranged 14 to 19% and 68 to 73% respectively. Stearic acid content of elevated stearic acid soybean event and cross line was stable over generation. However, in generation six and seven under field conditions the oleate levels decreased to 30-40%.

Decline of marine fish stocks due to over-fishing and the use of wild fish for diets of farmed fish pushed for development of sustainable land based alternative diets for farming fish such as soybean with respect to levels of very long chain omega-3 fatty acids, EPA and DHA. To generate EPA and the high value carotenoid, astaxanthin in soybean, we first created a two gene stack in soybean combining Δ6 and Δ15 desaturase genes, respectively. The resultant event designated 535-9 accumulates stearidonic acid in seed oil up to 35%. We have subsequently generated transgenic events that carry Δ6 elongase and Δ5 desaturase genes. Selected events derived from the latter have been crossed with event 535-9. EPA level in seed oil was up to 4%. In regards to astaxanthin production, we generated transgenic event carrying phytoene synthase, crtZ and crtW genes. Transgenic soybean produced up to 25μg/g astaxanthin. We crossed the four-gene EPA stack with the three gene astaxanthin stack to create a prototype soybean-based feedstock for aquaculture. We identified that the longer chain omega-3 fatty acids ETA and EPA, combined ranged from approximately 3-5% of the oil, along with astaxanthin and β-carotene accumulation from 23 to 44.8 μg/gr and 527 to 1139 μg/gr seed, respectively.