Tobacco mosaic virus Plant Virus Infections Local lesions

Tobacco mosaic virus

Plant Virus Infections Local lesions: cell to cell - may go undetected Beta-glucuronidase reporter

Plant Virus Infections Systemic infection: cell to cell, then into vascular system - rapid spread (centimetres / hr)

Cell to cell movement of TMV - dependent on “movement” protein - mapped ts mutation to 30 k. Da protein (no lesions at non-permissive temp) - can make transgenic plant expressing this protein complements ts mutation - protein increases (x 10) size of pores between cells (but virions still too big) - 30 k. Da protein also binds ss. RNA passes TMV genome into neighbouring cell - TMV movement through whole plant requires virion. coat protein mutants spread very poorly.

Plant Virus Curiosities Satellite viruses - require helper virus for replication functions - encodes own capsid protein - little or no sequence similarity with helper virus Tobacco necrosis virus (TNV) - normal icosahedral virus STNV = 1239 nucleotide RNA monocistronic m. RNA, encodes coat protein STNV = obligatory parasite of helper virus only TNV can "help" STNV some strain specificity replication of TNV reduced in presence of satellite virus

Plant Virus Curiosities Satellite RNAs - require helper virus for replication functions - may or may not have ORF (but not coat protein) - uses helper coat protein - preference for certain helper viruses - may enhance or attenuate disease of helper virus ∞ host plant Compare strains - can find "determinants for disease" in RNA - But don’t know how they function.