ASYMMETRIC INFECTIVITY OF PSEUDORECOMBINANTS OF CABBAGE LEAF CURL VIRUS AND SQUASH LEAF CURL VIRUS - IMPLICATIONS FOR BIPARTITE GEMINIVIRUSEVOLUTION AND MOVEMENT

The bipartite geminiviruses squash leaf curl virus (SqLCV) and cabbage leaf curl virus (CLCV) have distinct host ranges. SqLCV infects a bro ad range of plants within the Cucurbitaceae, including pumpkin and squ ash, and CLCV has a broad host range within Brassicaceae that includes cabbage and Arabidopsis thaliana. Despite this, the genomic A compone nts of these viruses share a high degree of sequence identity, particu larly in the gene encoding the replication protein AL1, and their comm on regions are 77% identical. However, there is unexpected sequence di versity in the common regions of the two CLCV genomic A and B componen ts, these being only 80% identical. Based on these sequence similariti es, we investigated the host range properties of pseudorecombinants of SqLCV and CLCV We found that in a pseudorecombinant virus consisting of the A component of CLCV and the a component of sqLCV, both componen ts replicated in tobacco protoplasts, and this pseudorecombinant was i nfectious and caused systemic disease in Nicotiana benthamiana, a comm on host to all bipartite geminiviruses. However, this pseudorecombinan t did not move systemically in pumpkin or Arabidopsis, despite the dem onstrated replication compatibility of the genome components. As a res ult of the greater sequence differences between the common regions, th e pseudorecombinant of SqLCV A and CLCV B components neither replicate d the CLCV B component nor systemically infected any of the hosts test ed. These findings demonstrate that for different geminiviruses with d istinct host ranges, the replication origins and AL1 proteins can be s ufficiently similar to permit infectious pseudorecombinants, but repli cation alone is not sufficient to cause systemic disease, and host ran ge may ultimately be limited at the level of movement. The results of this study further suggest that CLCV is an evolving virus that can pro vide insights into how new bipartite geminiviruses arise from mixed in fections. (C) lees Academic Press