Defective forms of cotton leaf curl virus DNA-A that have different combinations of sequence deletion, duplication,...

Tobacco and tomato plants inoculated at least 9 months previously with a Pakistani isolate of cotton leaf curl virus (CLCuV-PK), a whitefly-transmitted geminivirus, contained substantial amounts of circular dsDNA molecules that were mostly about half the size of CLCuV-PK dsDNA-A. They appeared to be derived from CLCuV-PK DNA-A by various combinations of sequence deletion, duplication, inversion and rearrangement and, in a few instances, insertion of sequences of unknown origin. Each of ten tobacco plants contained a different predominant form of such a defective molecule; however, all the forms contained the intergenic region and part of the AC1 (Rep) gene. Some of the forms contained novel open reading frames and might have a role in the evolution of variant geminiviruses. The defective components were not detected at 3 months after the original culture of CLCuV-PK was transmitted by whiteflies (Bemisia tabaci) from cotton to tomato but were present after a further 6 months. They were transmitted, along with full-length DNA-A, between tobacco and tomato plants by grafting and by B. tabaci.