This invention discloses a constitutive promoter for expression of foreign or endogenous coding sequences in plants, including dicotyledonous and monocotyledonous plants. The invention also discloses a chimeric nucleic acid construct comprising the promoter of the invention operably linked to a foreign or endogenous polynucleotide that codes for a protein of interest or a transcript capable of modulating expression of a target gene. The invention further discloses transformed plant cells, as well as differentiated plants and plant parts, containing the construct. Methods for diagnosis and treatment of viral infections, especially badnaviral infections, are also disclosed.