Potato mop-top virus (PMTV) causes spraing (unsightly brown arcs and rings in tubers of susceptible cultivars) and yellow chevrons or shortened internodes (mopping) in the leaves and stems of plants grown from infected tubers. Economic losses are due to poor tuber quality particularly in salad potato crops and PMTV is prohibited in seed potatoes exported to some countries.

It is transmitted in nature by a soil-borne plasmodiophorid (Spongospora subterranea) that itself causes the disease powdery scab on tubers. Both diseases are prevalent in cool and damp conditions, and are of particular importance to the Scottish potato (and seed potato) harvest.

The potato mop-top virus (PMTV) genome consists of three RNAs that encode proteins used to effect the main viral functions of replication, encapsidation, movement and transmission. PMTV uses a conserved modular set of three proteins known as triple gene block proteins (TGB) to allow movement of the genome through the plant, a feature common to viruses across eight different genera. PMTV, unlike many viruses, does not require coat protein for cell-cell or long distance movement. The three TGB movement proteins act in a coordinated manner, and are required for cell-to-cell and systemic movement of the virus genome.

Current research examines host-virus and virus-vector interactions to understand the molecular mechanisms underlying movement and spread of PMTV. We are employing reverse genetics techniques using infectious cDNA clones of PMTV and studying infection and transmission processes in a recently devised ‘hairy root’ system.

Figure 1: A. rhizogenes transformed potato roots. A = S. subterranea plasmodia inside a root hair.

Figure 1: A. rhizogenes transformed potato roots. A = S. subterranea plasmodia inside a root hair.