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30 Geminivirus DNA Replication

David M. Bisaro


Diseases caused by geminiviruses have long been recognized as a limitation to the cultivation of several important crops, including maize, cassava, bean, squash, cucurbits, and tomato, in tropical and subtropical regions of the world. More recently, geminivirus diseases, particularly those transmitted by whiteflies, have become an even greater threat to agriculture due to the appearance of a new and more aggressive whitefly biotype (Brown et al. 1995). This has renewed interest in the study of geminivirus pathogenesis and epidemiology and has stimulated work on the development of virus-resistant crop plants. For quite different reasons, geminiviruses have also attracted the attention of researchers concerned with fundamental aspects of plant molecular biology. In particular, their small DNA genomes and extensive reliance on host biosynthetic machinery make these viruses ideal model systems for the study of plant DNA replication and gene expression. Geminivirus genomes also have considerable potential as vectors for the expression of foreign genes in plants, although this potential has yet to be fully exploited. Because of their significance to plant pathology, plant molecular biology, and plant biotechnology, it is not surprising that geminiviruses have become the subjects of intensive research. As a result of efforts concentrated on a few model viruses, remarkable progress has been made toward understanding the mechanisms of viral replication and pathogenesis in the dozen years or so since the first molecular studies were initiated. Several recent reviews of this progress are available (Stanley 1991; Lazarowitz 1992; Mullineaux et al. 1992; Bisaro 1994). In this review, I...

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