TRANSGENIC ARABIDOPSIS LINES EXPRESSING GENE VI FROM CAULIFLOWER MOSAIC-VIRUS VARIANTS EXHIBIT A RANGE OF SYMPTOM-LIKE PHENOTYPES AND ACCUMULATE INCLUSION-BODIES

Gene VI of cauliflower mosaic virus (CaMV) is an important determinant of symptom expression during infection. We have constructed a series of transgenic Arabidopsis lines that express gene VI protein (P6) from two CaMV isolates (Bari-1 and Cabb B-JI) that cause mild and severe s ymptoms, respectively, in Arabidopsis, and from a recombinant virus (B aji-31) with a hybrid gene VI that causes very severe symptoms, From 4 1 transgenic lines analyzed, 17 showed symptom-like phenotypes that ra nged from mild vein chlorosis to severe chlorosis and stunting. P6 lev els in transgenic lines varied from undetectable in the lowest express ors to levels greater than those in CaMV-infected plants, There was a strong correlation between phenotype severity and the level of P6, and with the gene VI origin in the order, Baji-31 > B-JI > Bari-1. This w as similar to symptom severity in Arabidopsis infected with the respec tive CaMV variant, We also found that transgenic P6 accumulated in inc lusion bodies that were similar to those found in infected plants but lacking virions, We conclude that expression of P6, in the absence of virus replication, elicits a subset of the host symptom responses norm ally observed during infection and that the level, sequence, and possi bly the form of P6 are important in potentiating the process.