Chromosome condensation induced by geminivirus infection of mature plant cells

Tomato golden mosaic virus (TGMV) is a geminivirus that replicates its sing le-stranded DNA genome through double-stranded DIVA intermediates in nuclei of differentiated plant cells using host replication machinery. We analyze d the distribution of viral and plant DNA in nuclei of infected lea ces usi ng fluorescence in situ hybridization (FISH), TGMV-infected nuclei showed u p to a sixfold increase in total volume and displayed a variety of viral DN A accumulation patterns. The most striking viral DNA patterns mere bright, discrete intranuclear compartments, but diffuse nuclear localization was al so observed. Quantitative and spatial measurements of high resolution 3-dim ensional image data revealed that these compartments accounted for 1-18% of the total nuclear volume or 2-45% of the total nuclear FISH signals. In co ntrast, plant DNA was concentrated around the nuclear periphery. In a signi ficant number of nuclei, the peripheral chromatin was organized as condense d prophase-like fibers. A combination of FISH analysis and indirect immunof luorescence with viral coat protein antibodies revealed that TGMV virions a re associated with the viral DNA compartments. However the coat protein ant ibodies failed to cross react with some large viral DNA inclusions, suggest ing that encapsidation may occur after significant viral DNA accumulation. Infection by a TGMV mutant with a defective coat protein open reading frame resulted in fewer and smaller viral DNA-containing compartments. Neverthel ess, nuclei infected with the mutant virus increased in size and in some ca ses showed chromosome condensation. Together, these results established tha t geminivirus infection alters nuclear architecture and can induce plant ch romatin condensation characteristic of cells arrested in early mitosis.