Wei LiFollow

Date of Completion

5-4-2017

Embargo Period

5-1-2018

Major Advisor

Yi Li

Associate Advisor

Gerald Berkowitz

Associate Advisor

Richard McAvoy

Associate Advisor

Huan-zhong Wang

Field of Study

Plant Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Transgenic technology provides a powerful tool for woody plant improvement. However, the full utilization of this technology has been stagnant due to gene flow and food safety concerns. This dissertation describes two transgene containment techniques that are particularly useful for woody plants. The first one is a flowerless plant technique that can be used to prevent pollen- and seed-mediated transgene flow. We developed an artificial promoter sequence, rPTAG2I, and demonstrated that this sequence is floral-predominant in tobacco with no detectable activity in the vegetative tissues of tobacco and poplar. Transgenic tobacco plants expressing the Diphtheria toxin A (DT-A) gene driven by the rPTAG2I promoter exhibited a flowerless phenotype with enhanced shoot and root biomass. Over two growing seasons in the field, rPTAG2I::DT-A transgenic poplar plants displayed similar vegetative growth compared to wild type. The second technique used a root-predominant gene promoter (SbUGT) to drive the expression of an auxin biosynthetic gene (iaaM) and a cytokinin degradation gene (CKX) to improve rootstocks. We demonstrated that expression of both the iaaM and CKX genes, predominantly in roots, inhibited lateral bud release and enhanced both root initiation and biomass of rootstock. Also, the grafting success rates were improved even though non-transgenic scions were used. We have further shown that the use of the iaaM+CKX transgenic rootstocks led to improved non-transgenic scion growth even when the lateral buds on rootstock remained intact. Because of these characteristics, our technique takes advantages of transgenic technology but also eliminates the concerns of gene flow from flowers and fruits. In summary, the development of both the flowerless and iaaM+CKX rootstock techniques may provide useful tools to address gene flow and food safety concerns over transgenic woody plant species.

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