Integrase diversity and transcription of the maize retrotransposonGrande

Abstract

Grande is an abundant gypsy-like retrotransposon present in the genera Zea and Tripsacum. Related retro transposon families can be found in sorghum, rice, and barley, but not in wheat or rye. We have amplified and sequenced several copies of part of the integrase domain derived from the Zea mays, Zea diploperennis, and Tripsacum dactyloides genomes. There are no significant differences in divergence or clustering between the integrase sequences of these species. The substitution rate for synonimous sites was found to be higher than those of non-synomymous sites; this indicates that Grande integrase has been under purifying selection for function. Grande is transcribed in leaves. The transcripts show sequence diversity similar to that of genomic sequences, but belong to restricted clades; this indicates that only some evolutionary branches of Grande have retained transcriptional competence.Key words: maize, plant genome, retrotransposon, Zea diploperennis, Zea genus.