A process of expressing a sequence of interest in a plant, plant part, orplant cell culture, comprising: (a) providing a plant, plant part, or plantcell culture containing in cell nuclei a heterologous DNA having a sequenceencoding an RNA replicon operably linked or linkable to a transcriptionpromoter, wherein said sequence encoding an RNA replicon contains (i)sequences for replicon function of said RNA replicon, said sequences beingderived from a sequence of a plant RNA virus, (ii) a sequence of interest,whereby said sequences for replicon function exhibit at selected localities ofsaid sequences of said plant RNA virus function~conservative differences fromsaid sequence of said plant RNA virus, said differences causing an increasedfrequency of replicon formation compared to an RNA replicon not exhibitingsaid differences； and (b) causing expression of said sequence of interest.
