Characterization of circular DNA molecules from cotton plants with leaf curl disease

摘要

Leaf curl disease of cotton is the most devastating disease of cotton in Pakistan. Phi29 DNA polymerase that amplifies circular DNA molecules was used to characterize circular DNA molecules found in infected plants. Phi29 DNA polymerase amplified product was digested with different restriction enzymes and was randomly cloned. Clones were sequenced and their homology to DNA sequences available in NCBI database was estimated. The usual components consisting of begomoviruses and their associated satellites reported previously from cotton were found associated with the disease. The comparison also identified clones of non-viral origin. The most prominent among them were plasmid-like molecules of chloroplast origin. These molecules were only amplified in infected plants and were not at detectable levels in healthy plants. Other circular molecules included transposon sequences of cotton origin, their recombinants and derivatives of varying sizes. Other circular molecules showed homology to sequences related to host defense such as resistance genes, Argonaute etc. There were other circular molecules that showed no homology to any DNA sequence in the database. Some molecules were recombinant of known and unknown DNA sequences. We propose that these circular molecules are amplified due to suppression of RNA silencing based host defense by begomovirus infection.