A plant processed pseudogene

Abstract

Processed pseudogenes are a common feature of mammalian multi-gene families and 'single-copy' genes^1–3. They are considered to result from integration into the genome of reverse transcripts of cytoplasmic poly(A) ⁺ messenger RNA of genes that are expressed in the germ line. The paucity or absence of processed pseudogenes in animal groups other than mammals, despite the presence of endogenous viral retroposons encoding reverse transcriptase⁴, has led to the suggestion that this disparity might be the result of differences in the duration of gametogenesis³. In contrast to animals, plants lack a germ line: plant gametes differentiate from cells that have been actively engaged in organizing the somatic tissue of the plant, in the apical meristem. Pseudogenes of somati-cally expressed genes could therefore appear eventually in the gametes. Although reverse transcription is known to be involved in the replication of the cauliflower mosaic virus^5–7, and retrotrans-posons have been described in wheat and maize^8–10, surprisingly no plant processed pseudogene has been reported. We report here the nucleotide sequence of an actin gene from potato (Solanum tuberosum) which has all the characteristic features of a typical mammalian processed pseudogene. This potato processed pseudogene might be the first of many that are yet to be discovered. Alternatively, it might be a rare event because some, as yet, unknown factors affect the different rates of pseudogene production in animals and plants.