The mode of cauliflower mosaic virus propagation in the plant allows rapid amplification of viable mutant strains

Abstract

We inoculated the leaves of turnip plants (Brassica campestris spp. rapa cv. Just Right) with two cauliflower mosaic viruses (CaMVs) with different small mutations in a dispensable region of the viral genome, and followed the spread of the virus infection through the plant. Surprisingly, analysis of viral DNA in single primary chlorotic lesions revealed the presence of both mutants. In contrast, the secondary chlorotic lesions and systemically infected leaves contained virus molecules of either one or the other type only. Infection of plants with different ratios of the two reporter viruses showed that this ratio is not conserved during systemic virus spread. Infection with CaMV DNA in the form of heteroduplexes containing a single mismatched base pair, in which each strand carried a distinct diagnostic marker, provided us with evidence that the mismatch was subjected to a repair process in the host plant.

Large Bottleneck Size in Cauliflower Mosaic Virus Populations during Host Plant Colonization

“…Previous studies, based on co-infection of turnip plants by two distinct CaMV variants with seemingly equal growth rate, have compared the variant ratios in the initial inoculum and in resulting systemically infected plants. No differences were observed when concentrated virus particles were used for inoculation [33], whereas stochastic fluctuations were detectable when inoculum consisted in viral DNA prepared from infectious clones [34], presumably due to the lower infectivity of DNA preparations, engendering a stochastic founding effect in the latter case. These two studies indicate that indeed the inoculation process could induce unwanted fluctuations in repeated inoculations and prompted us to use virus particles enriched preparation for the purpose of our experiment (albeit development of systemic infection in between the two observation time points chosen in our protocol should not be affected by inoculation variations).…”

Phylogenetic relationships reveal recombination among isolates of cauliflower mosaic virus

“…Plants infected as little as 2 days previous are cross-protected against infection with a second isolate (Zhang and Melcher 1989). Also, in mixed infections, lesions that develop on noninoculated leaves contain one or the other of the coinoculated isolates, but not both (Riederer et al 1992). Thus, though recombination is possible, the opportunity for its occurrence may not be frequent.…”

Variation in Biological Properties of Cauliflower Mosaic Virus Clones

“…In contrast, infections by certain virus isolates or those resulting from coinoculations by different molecular types have been shown to contain mixtures of progeny molecules some of which have had major deletions generated in vivo (Hirochika et al, 1985;Zhang & Melcher, 1989;Vaden & Melcher, 1990;Scholthof et al, 1991 ;Pennington & Melcher, 1993). However, systemic infections initiated by mechanical inoculation appear to result from mobilization of one or a small number of molecules from the inoculation site (Riederer et al, 1992) suggesting that virus genome variants arise de novo during each infection cycle and are maintained as a minor proportion of an otherwise uniform population. Some of these new variants should possess novel biological properties that are either suppressed by the predominating genome type or appear as infections causing altered symptoms during passage.…”