Tomato yellow leaf curl virus, the intracellular dynamics of a plant DNA virus.

UNLABELLED: SUMMARY Tomato yellow leaf curl virus is a geminivirus, transmitted by whitefly (Bemisia tabaci) and causing the most destructive disease of tomato throughout the Mediterranean region, the Middle East and the tropical regions of Africa and Central America. Affected plants produce either no fruits or a few small fruits. Since it is an ssDNA virus which replicates in the host cell nucleus, the molecular mechanisms involved in the viral nuclear import have been the focus of our studies in recent years and results as well as prospects will be discussed. TAXONOMY: Tomato yellow leaf curl virus (TYLCV) is a ssDNA plant virus, a member of the family Geminiviridae, of the genus Begomovirus. Physical properties: TYLCV, like all members of Geminiviridae, has geminate (twinned) particles, 18-20 nm in diameter, 30 nm long, apparently consisting of two incomplete T = 1 icosahedra joined together in a structure with 22 pentameric capsomers and 110 identical protein subunits (Fig. 1). Disease symptoms: Symptoms become visible in tomato in approximately 2-3 weeks after infection (Fig. 2). Leaf symptoms include chlorotic margins, small leaves that are cupped, thick and rubbery. The majority (up to 90%) of flowers abscise after infection, and therefore few fruits are produced. In Israel and elsewhere, weeds bridge the gap as potential perennial host and source of the virus between tomato growing seasons. Disease control: Control of TYLCV is currently based on insecticide treatments and/or physical barriers against the insect vector (Bemisia tabaci), and on tomato breeding programs based on introgression of resistance or tolerance from wild species to cultivated tomato. Useful website: <http://www.danforthcentre.org/iltab/geminiviridae/>