Genetic engineering of mint to confer desired traits

Xia Li, Purdue University

Abstract

Peppermint and spearmint are specialty crops of considerable economic value of mint essential oil. The primary constraint to oil production is crop yield loss attributable to pests and pathogens. However, host plant resistance to pests and diseases has not been achieved through conventional breeding because of their steribility. Transgenic approaches provide a powerful tool for utilizing biotechnology in mint crop improvement. In this study, substantial improvement in peppermint genetic transformation has been achieved so that the frequency of transgenic plants regenerated was more than 20-fold greater than with the original protocol at 1%. Essential modifications were made to conditions for Agrobacterium tumefaciens co-cultivation, results demonstrated that deletion of coconut water from the co-cultivation medium resulted in substantially increased transient and stable GUS gene expression. The bar gene encoding phosphinothricin acetyltransferase that inactivates glufosinate-ammonium was transformed into peppermint. One hundred and forty-two transgenic peppermint plants were obtained and examined for herbicide resistance in the greenhouse after foliar application of glufosinate herbicide. Among them, forty-four lines were evaluated for herbicide resistance and agricultural performance under field conditions. Results showed that all transgenic plants had greater herbicide resistance, albeit a large variation was obtained among the transgenic lines. The transgenic line 94-2 was highly herbicide resistant, and no leaf injury, reduction in plant biomass and oil yield were observed to a 8-fold recommended application dosage. Analysis of oil profiles showed that most plants produced a typical commercially acceptable peppermint oil. Results demonstrated that overexpression of the bar gene effectively protected transgenic peppermint plants. Protocols and media constituents for efficient in vitro plant regeneration of Native Spearmint have been defined. Adventitious shoots were initiated either directly from morphogenetically competent cells of explants or primary callus. Explants from basal portions of leaves at the bottom of the 2-month old shoots exhibited the greatest morphogenetic capacity. High frequency of meristemoids and morphogenetic callus were initiated from explants cultured onto a Murashige and Skoog basal media supplemented with 4 mg/L thidiazuron and 25% (vol/vol) coconut water. Bud and shoot development require removal of both TDZ and CW from the media. Peppermint and spearmint are specialty crops of considerable economic value of mint essential oil. The primary constraint to oil production is crop yield loss attributable to pests and pathogens. However, host plant resistance to pests and diseases has not been achieved through conventional breeding because of their steribility. Transgenic approaches provide a powerful tool for utilizing biotechnology in mint crop improvement. In this study, substantial improvement in peppermint genetic transformation has been achieved so that the frequency of transgenic plants regenerated was more than 20-fold greater than with the original protocol at 1%. Essential modifications were made to conditions for Agrobacterium tumefaciens co-cultivation, results demonstrated that deletion of coconut water from the co-cultivation medium resulted in substantially increased transient and stable GUS gene expression.

Degree

Ph.D.

Advisors

Weller, Purdue University.

Subject Area

Molecular biology|Botany

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