| Summary: | <p>Abstract</p> <p>Background</p> <p><it>DAYSLEEPER</it> encodes a domesticated transposase from the hAT-superfamily, which is essential for development in <it>Arabidopsis thaliana</it>. Little is known about the presence of <it>DAYSLEEPER</it> orthologs in other species, or how and when it was domesticated. We studied the presence of <it>DAYSLEEPER</it> orthologs in plants and propose a model for the domestication of the ancestral <it>DAYSLEEPER</it> gene in angiosperms.</p> <p>Results</p> <p>Using specific BLAST searches in genomic and EST libraries, we found that <it>DAYSLEEPER</it>-like genes (hereafter called <it>SLEEPER</it> genes) are unique to angiosperms. Basal angiosperms as well as grasses (Poaceae) and dicotyledonous plants possess such putative orthologous genes, but <it>SLEEPER</it>-family genes were not found in gymnosperms, mosses and algae. Most species contain more than one <it>SLEEPER</it> gene. All <it>SLEEPER</it>s contain a C<sub>2</sub>H<sub>2</sub> type BED-zinc finger domain and a hATC dimerization domain. We designated 3 motifs, partly overlapping the BED-zinc finger and dimerization domain, which are hallmark features in the <it>SLEEPER</it> family. Although <it>SLEEPER</it> genes are structurally conserved between species, constructs with <it>SLEEPER</it> genes from grapevine and rice did not complement the <it>daysleeper</it> phenotype in Arabidopsis, when expressed under control of the <it>DAYSLEEPER</it> promoter. However these constructs did cause a dominant phenotype when expressed in Arabidopsis. Rice plant lines with an insertion in the <it>RICESLEEPER</it>1 or 2 locus displayed phenotypic abnormalities, indicating that these genes are functional and important for normal development in rice. We suggest a model in which we hypothesize that an ancestral hAT transposase was retrocopied and stably integrated in the genome during early angiosperm evolution. Evidence is also presented for more recent retroposition events of <it>SLEEPER</it> genes, such as an event in the rice genome, which gave rise to the <it>RICESLEEPER</it>1 and 2 genes.</p> <p>Conclusions</p> <p>We propose the ancestral <it>SLEEPER</it> gene was formed after a process of retro-transposition during the evolution of the first angiosperms. It may have acquired an important function early on, as mutation of two <it>SLEEPER</it> genes in rice, like the <it>daysleeper</it> mutant in <it>A. thaliana</it> gave a developmental phenotype indicative of their importance for normal plant development.</p>
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