Controlling Transgene Escape in Genetically Modified Grasses

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Abstract

Trait improvement of turfgrass through genetic engineering is important to the turfgrass industry and the environment. However, the possibility of transgene escape to wild and non-transformed species raises commercial and ecological concerns. Male sterility provides an effective way for interrupting gene flow. We have designed and synthesized two chimeric gene constructs consisting of a rice tapetum-specific promoter (TAP) fused to either a ribonuclease gene barnase, or the antisense of a rice tapetum-specific gene rts. Both constructs were linked to the bar gene for selection by resistance to the herbicide glufosinate. Using Agrobacterium-mediated transformation, we have successfully introduced those gene constructs into creeping bentgrass (cv Penn-A-4), producing a total of 219 stably transformed individual events. Tapetum-specific expression of barnase or antisense rts gene did not affect the vegetative phenotype compared with the control plants, and male-sterile flowers were obtained with both constructs. Microscopic studies confirmed the failure of mature pollen formation in male-sterile transgenics. Mendelian segregation of herbicide tolerance and male sterility has been observed in T1 progeny derived from crosses with wild-type plants. Male sterility in transgenic grasses provides the best tool to evaluate gene flow in genetically modified perennial plants and should facilitate the application of genetic engineering in producing environmentally responsible grasses with enhanced traits.