Mass Transfer Phenomena and Biological Membranes

Abstract

Mutants of the monopartite geminivirus beet curly top hybrigeminivirus (BCTV) have been screened for infectivity, systemic movement, replication and symptom development in Arabidopsis thaliana. As known by coding for coat proteins, the R1 mutant was not infectious and did not move systemically. R2, R3 and L2/L3 mutants produced milder symptoms compared with the wild type BCTV but the infectivity was reduced by 40-60%. R2 ORF is thought to be involved in the regulation of ssDNA and dsDNA accumulation because only dsDNA accumulated in R2 infected organs. Disruption of ORF L4 resulted in reduced infections, but the viral DNA accumulated in infected organs from roots to shoot tips as much as the wild type BCTV in the ecotype Sei-O. In addition, 4 mutants did not produce callus-like tissues on infected organs, suggesting that the L4 ORF may play a role in the induction of host cell division by virus infection. This result was supported by the patterns of mRNA expression and promoter analysis of the cell cycle marker gene, cyc1, on Arabidopsis. cyc1 mRNA accumulated in symptomatic organs infected by wild type BCTV but not by the L4 mutant. It is concluded that the BCTV L4 ORF is essential for symptom development, especially callus-like formation in infected organs.