Activities of CaMV 35S andnospromoters in pollen: implications for field release of transgenic plants

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Abstract
The expression of foreign genes in pollen may pose potential problems in the field release of transgenic plants, since pollen represents a route whereby foreign genes and their products may escape into the wider environment. The possible risks posed by cross-hybridization with wild relatives have been extensively explored, but problems that may arise due to the expression of foreign gene products in pollen have not been so widely studied. The activities of the CaMV 35S and nos promoters in pollen in populations of stably transformed plants and in transient expression analysis are described. These promoters are commonly used in all areas of plant molecular biology research and their expression patterns will be of interest to those involved in field release studies. The results show that both promoters had no detectable pollen activity in Arabidopsis, but both showed activity in tobacco pollen. The CaMV 35S-gus gene fusion showed heritable expression levels in tobacco pollen of up to a maximum of 64.6 pmol 4-MU min−1 mg −1 total protein. nos promoter activity in transgenic tobacco pollen was highly variable, with GUS activities ranging from undetectable levels up to 2561 pmol 4-MU min−1 mg−1 total protein within the transgenic population. Histochemical staining of anther sections from 10–12 mm buds revealed that the CaMV 35S promoter had some activity in the vascular bundle, stomium and tapetum, while GUS expression from the nos promoter in sporophytic tissues was confined entirely to the stomium.

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