GENE-I MUTANTS OF PEANUT CHLOROTIC STREAK VIRUS, A CAULIMOVIRUS, REPLICATE IN PLANTS BUT DO NOT MOVE FROM CELL-TO-CELL

Gene I of peanut chlorotic streak virus (PCISV), a caulimovirus, is ho mologous to gene I of other caulimoviruses and may encode a protein fo r virus movement, To evaluate the function of gene I, several mutation s were created in this gene of an infectious, partially redundant clon e of PCISV. Constructs with an in-frame deletion and a single amino ac id substitution in gene I were not infectious, To test for replication of these mutants in primarily infected cells, an immunosorbent PCR te chnique was devised. Virus particles formed by mutants in plants were recovered by binding to antivirus antibodies on a solid matrix and DNa se treated to discriminate against residual inoculum, and DNA of trapp ed virions was subjected to PCR amplification. Gene I mutants were sho wn to direct formation of encapsidated DNA as revealed by a PCR produc t, Control gene V mutants (reverse transcriptase essential for replica tion) did not yield a PCR product, Quantitative PCR allowed estimation of the proportion of cells initially infected by gene I mutants and t he amount of extractable virus per cell. It is concluded that PCISV ge ne I encodes a movement protein and that the immunoselection-PCR techn ique is useful in studying subliminal virus infection in plants.