The MAR-mediated reduction in position effect can be uncoupled from copy number-dependent expression in transgenic plants

• Published in: The Plant cell Vol. 7; no. 5; pp. 599 - 609
• Main Authors: Mlynarova, L. (Centre for Plant Breeding and Reproduction Research, Wageningen, The Netherlands.), Jansen, R.C, Conner, A.J, Stiekema, W.J, Nap, J.P
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Physiologists 01-05-1995
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; ADN RECOMBINADO; ADN RECOMBINE; CAULIMOVIRUS; Chromatin; CHROMATINE; CROMATINA; Depopulation; EXPRESION GENICA; EXPRESSION DES GENES; FOSFOTRASFERASA; GENE; Gene dosage; Gene expression; GENES; Genetic variation; GLICOSIDASAS; GLYCOSIDASE; LISOZIMA; LYSOZYME; NICOTIANA TABACUM; PHOSPHOTRANSFERASE; Plant cells; PLANTAS TRANSGENICAS; PLANTE TRANSGENIQUE; Plants; POLLO; Population mean; POULET; TRANSFORMACION GENETICA; TRANSFORMATION GENETIQUE; Transgenes; Transgenic plants; VIRUS DE LAS PLANTAS; VIRUS DES VEGETAUX
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.7.5.599

To study the role of matrix-associated regions (MARs) in establishing independent chromatin domains in plants, two transgenes were cloned between chicken lysozyme A elements. These transgenes were the neomycin phosphotransferase (NPTII) gene under control of the nopaline synthase (nos) promoter and the beta-glucuronidase (GUS) gene controlled by the double cauliflower mosaic virus (dCaMV) 35S promoter. The A elements are supposed to establish an artificial chromatin domain upon integration into the plant DNA, resulting in an independent unit of transcriptional regulation. Such a domain is thought to be characterized by a correlated and position-independent, hence copy number-dependent, expression of the genes within the domain. The presence of MARs resulted in a higher relative transformation efficiency, demonstrating MAR influence on NPTII gene expression. However, variation in NPTII gene expression was not significantly reduced. The selection bias for NPTII gene expression during transformation could not fully account for the lack of reduction in variation of NPTII gene expression. Topological interactions between the promoter and A element may interfere with the A element as a domain boundary. In contrast, the GUS gene on the same putative chromatin domain showed a highly significant reduction in variation of gene expression, as expected from previous results. Surprisingly, no copy number-dependent GUS gene expression was observed: all plants showed approximately the same GUS activity. We concluded, therefore, that dCaMV 35S-GUS gene expression in mature tobacco plants is regulated by some form of dosage compensation