Movement of a caulimovirus and tobamoviruses

Scope and method of study. This study has two objectives: (1) To test whether the functions of tobacco mosaic virus (TMV) movement protein (MP) and cauliflower mosaic virus (CaMV) MP are exchangeable and what is the role of TMV P30 and CaMV P38 in host specificity. (2) To find the genetic determinants of turnip host specificity in tobamoviruses. The infectivity of chimeras made between TMV and CaMV by exchanging the MP genes or parts of the MP genes, and chimeras made between TMV and turnip vein clearing virus (TVCV) was tested on tobacco and turnip plants.;Findings and conclusions. This study has five major findings. (1) TMV chimeras with TMV MP gene or parts of TMV MP gene replaced were not infectious on tobacco plants. (2) CaMV chimeras with CaMV MP gene or parts of CaMV gene replaced were not infectious on tobacco and turnip plants. (3)TMV with its MP replaced by CaMV MP spread much slower on inoculated leaves than wild type TMV and other TMV chimeras on TMV MP transgenic plants. (4) Viruses able to infect tobacco were recovered after passage of two TMV chimeras through TMV MP transgenic tobacco plants. (5) A TVCV chimera with the TVCV replicase gene replaced by that of TMV and a TVCV chimera with the TVCV MP gene replaced by that of TMV moved like TVCV and TMV on tobacco plants, but their movement on turnip plants was limited. Four conclusions were drawn from the findings. (1) Functions of CaMV and TMV MP are not exchangeable. (2) CaMV MP interferes with TMV MP function(s). (3) Recombination between TMV chimeras and TMV MP transgene may occur. (4) Both TMV replicase and MP gene are genetic factors limiting TMV movement on turnip plants.