Contribution of the satellite encoded gene βC1 to cotton leaf curl disease symptoms

Cotton leaf curl disease (CLCuD) is caused by one of seven begomoviruses in conjunction with a specific satellite; CLCuD DNA β. Associated with some monopartite begomoviruses, DNA β components encode a single gene (βC1) which mediates satellite functions. We have investigated the contribution the satellite, specifically βC1, makes to CLCuD symptoms in the absence of the helper begomovirus. Systemic expression of CLCuD-βC1 from a Potato virus X (PVX) vector induces bona fide CLCuD disease symptoms in Nicotiana tabacum plants, including enations, swollen veins and vein darkening. These contrast with the mild symptoms of PVX in this host. Analysis of thin sections across enations induced by PVX expressing βC1 shows the structure of the enation to be identical to those induced by CLCuD DNA β in conjunction with a helper begomovirus. These results demonstrate that CLCuD βC1 is the major determinant of symptoms for the CLCuD complex.