HETEROLOGOUS COMPLEMENTATION BY GEMINIVIRUS AL2 AND AL3 GENES

The geminivirus group is diverse and contains viruses which can be pla ced into three distinct subgroups on the basis of their genome organiz ation and biological properties. However, most dicot-infecting geminiv iruses possess AL1, AL2, and AL3 open reading frames. AL1 encodes the only viral protein that is absolutely required for replication, AL2 co des for a protein that transactivates the expression of virion sense p romoters, and AL3 specifies a protein that enhances viral DNA replicat ion. in the studies presented here, we examined the functional specifi city of the AL1, AL2, and AL3 gene products of subgroup II and subgrou p III geminiviruses. Surprisingly, we found that all viruses tested we re able to produce a gene product which complemented the reduced DNA r eplication phenotype of a tomato golden mosaic virus (TGMV) AL3 mutant . We also found that all bipartite subgroup Ill viruses tested produce d a protein that could transactivate the virion sense promoters of a T GMV AL2 mutant, although a subgroup II virus did not, In contrast, the replication activity of ALI protein proved to be virus specific. The data are discussed with regard to the functions of these proteins in v iral replication and their practical significance for the development of crop protection strategies. (C) 1994 Academic Press, Inc.