PhD Exit Seminar
Zhifen Zhang, PhD Candidate
PhD Exit Seminar
Title: Use of genetic transformation technology in oil crops: soybean and sunflower
Abstract: Although genetic transformation technology has been routinely used to produce commercial varieties of soybean, the most important oil crop, transformation approaches for sunflower, the fourth most important oil crop, have only been occasionally used in basic research and no commercial transgenic varieties have been released. In Part, this may be due to the lack of reliable and efficient regeneration and transformation methods for sunflower. Using a well-characterized soybean transformation system, a family of soybean promoters associated with early somatic embryo induction was characterized following introduction and tracking of GFP expression in embryogenic tissues and transgenic soybean plants. These promoters displayed tissue specific expression and were active in newly induced soybean somatic embryos. In sunflower, regeneration and transformation methods were studied and improved. Germination of sunflower seeds on a cytokinin-containing medium led to a 6-fold increase in shoot induction from leaf tissues. Use of a short pulse treatment of cotyledon tissue on a shoot induction medium gave more than a 14-fold increase in the numbers of well-developed shoots. A micrografting technique was developed for plant recovery with over 50% graft survival. Using sunflower cotyledons, a new Agrobacterium-mediated transformation procedure using low inoculum/long co-culture yielded 30x more transgenic shoots than the standard protocol using high inoculum/short co-culture. Expression analysis via qRT-PCR showed lower expression levels of genes related to plant defense response in the explants treated with low inoculum, suggesting that the low inoculum reduced the induction of plant defense, which impacts plant transformation and regeneration. The use of low inoculum/long co-culture has great potential for improving Agrobacterium-mediated transformation of other plant species.