AMPLIFICATION AND EXPRESSION OF THE BETA-GLUCURONIDASE GENE IN MAIZE PLANTS BY VECTORS BASED ON MAIZE STREAK VIRUS

Maize streak virus (MSV) is a geminivirus infecting monocotyledonous p lants. Its genome consists of one molecule of circular, single-strande d DNA of 2.7 kb. The viral DNA can be efficiently introduced into maiz e plants by agroinfection which results in systemic infection. To expl ore the potential of MSV as a replicative gene vector, a reporter gene coding for beta-glucuronidase (GUS) was inserted into the noncoding r egion of the viral genome. The resulting construct (MSV-GUS) of about 5.9 kb was still able to replicate in cells of maize plants although i t was unable to induce viral symptoms. This replication led to a five to 10-fold increase in the mean number of GUS-positive spots per plant as compared with infections with the GUS gene without the MSV replico n. MSV-D-GUS, which differed from MSV-GUS by the deletion of genes V1 and V2 encoding a putative movement protein and the coat protein, resp ectively, also replicated and produced even more GUS-positive spots. I n both MSV-GUS- and MSV-D-GUS-infected plants, the GUS-positive spots were located mainly on the veins of leaves whose primodia had already developed at the time of inoculation and never on the leaves developin g later. Thus, neither viral construct was able to move systemically, most probably because the DNAs were too large to be packaged.