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The Rb7 Matrix Attachment Region Increases the Likelihood and Magnitude of Transgene Expression in Tobacco Cells: A Flow Cytometric Study

^a Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695-7614
^b Department of Botany, North Carolina State University, Raleigh, North Carolina 27695-7612
^c Department of Crop Science, North Carolina State University, Raleigh, North Carolina 27695-7620

² To whom correspondence should be addressed. E-mail steven_spiker{at}ncsu.edu; fax 919-515-3355.

Many studies in both plant and animal systems have shown that matrix attachment regions (MARs) can increase expression of transgenes in whole organisms or cells in culture. Because histochemical assays often indicate variegated transgene expression, a question arises: Do MARs increase transgene expression by increasing the percentage of cells expressing the transgene (likelihood), by increasing the level of expression in expressing cells (magnitude), or both? To address this question, we used flow cytometry to measure green fluorescent protein (GFP) expression in individual tobacco (Nicotiana tabacum) cells from lines transformed by Agrobacterium tumefaciens. We conclude that MAR-mediated overall increases in transgene expression involve both likelihood and magnitude. On average, cell lines transformed with the Rb7 MAR-containing vector expressed GFP at levels 2.0- to 3.7-fold higher than controls. MAR lines had fewer nonexpressing cells than control lines (10% versus 45%), and the magnitude of GFP expression in expressing cells was greater in MAR lines by 1.9- to 2.9-fold. We also show that flow cytometry measurements on cells from isogenic lines are consistent with those from populations of independently transformed cell lines. By obviating the need to establish isogenic lines, this use of flow cytometry could greatly simplify the evaluation of MARs or other sequence elements that affect transgene expression.