CHARACTERIZATION OF ORGAN SPECIFIC PROMOTERS IN TRANSGENIC WHEAT

Authors: SOMLEVA, MARIA - UNIV OF CA-DAVIS; Blechl, Ann

Submitted to: National Fusarium Head Blight Forum
Publication Type: Proceedings
Publication Acceptance Date: 10/28/2004
Publication Date: 12/11/2004
Citation: Somleva, M.N., Blechl, A.E. 2004. Characterization of organ specific promoters in transgenic wheat. National Fusarium Head Blight Forum Proceedings. P. 263-267

Interpretive Summary: Genetic engineering is a promising approach to increase plant resistance to pests, but there is concern that this technology will result in the introduction of new proteins into the food supply. In applications where edible parts of the plant are not targets for pathogen infection, the introduced protective proteins are not needed in the grain or fruit. For example, to make wheat resistant to the fungal pathogen, Fusarium, the protective proteins would only be needed in the organs surrounding the young flower because they are the most vulnerable to early infection. The experiments in this manuscript identify a regulatory gene sequence from barley, the Lem1 promoter, which is active in the outer green tissues of recently fertilized wheat flowers, but not in developing wheat seeds. This promoter is ideal for controlling accumulation of anti-Fusarium proteins: they would be found when and where they are needed to stop infection by the fungus. At the same time, use of this promoter would preclude foreign proteins from accumulating in the grain of such transgenic plants. The availability of specific promoters such as Lem1 will allow biotechnologists to more precisely target foreign proteins to the parts of transgenic plants where they are needed, while excluding them from the food supply.

Technical Abstract: Genetic engineering is a promising approach to increase plant resistance to fungal pathogens, including Fusarium. The effectiveness of an antifungal gene in planta is determined by its expression levels in vulnerable host tissues and by the timing of its expression such that suitable levels of the encoded protein accumulate before the infection. Expression of anti-Fusarium (AF) genes in the glume and lemma is desirable for both wheat and barley, because these organs comprise the outer most protective barrier encasing the reproductive organs. In this study, we investigated the organ- and developmental specificity of two promoters in stable wheat transformants. A promoter from a maize glutamine synthase gene, GS, is only expressed in the pericarp and in the scutellum of mature embryos. Thus, it is not suitable for use in AF constructs. The promoter from a barley floret-expressed gene, Lem1, is active in the organs surrounding the developing wheat floret and in the rachis at anthesis, but not in young or mature seeds. This pattern is ideal for expression of AF genes in wheat. To facilitate the use of the Lem1 promoter for genetic engineering, vectors were constructed that allow efficient placement of coding sequences under its control. The use of tissue-specific promoters such as Lem1 allows biotechnologists to better control transgene expression and to target foreign protein accumulation to the parts of the plant where it is needed for improvement of the trait of interest.