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Proc Natl Acad Sci U S A. 2002 Sep 3;99(18):11975-80. Epub 2002 Aug 16.

Stimulation of the cell cycle and maize transformation by disruption of the plant retinoblastoma pathway.

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  • 1Pioneer Hi-Bred, International, Inc., Johnston, IA 50131, USA.


The genome of the Mastreviruses encodes a replication-associated protein (RepA) that interacts with members of the plant retinoblastoma-related protein family, which are putative cell cycle regulators. Expression of ZmRb1, a maize retinoblastoma-related gene, and RepA inhibited and stimulated, respectively, cell division in tobacco cell cultures. The effect of RepA was mitigated by over-expression of ZmRb1. RepA increased transformation frequency and callus growth rate of high type II maize germplasm. RepA-containing transgenic maize calli remained embryogenic, were readily regenerable, and produced fertile plants that transmitted transgene expression in a Mendelian fashion. In high type II, transformation frequency increased with the strength of the promoter driving RepA expression. When a construct in which RepA was expressed behind its native LIR promoter was used, primary transformation frequencies did not improve for two elite Pioneer maize inbreds. However, when LIR:RepA-containing transgenic embryos were used in subsequent rounds of transformation, frequencies were higher in the RepA+ embryos. These data demonstrate that RepA can stimulate cell division and callus growth in culture, and improve maize transformation.

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