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Structurally Different Alleles of the ath-MIR824 microRNA Precursor Are Maintained at High Frequency in Arabidopsis thaliana
Juliette de Meaux, Jin-Yong Hu, Ute Tartler and Ulrike Goebel
Proceedings of the National Academy of Sciences of the United States of America
Vol. 105, No. 26 (Jul. 1, 2008), pp. 8994-8999
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/25462906
Page Count: 6
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In plants and animals, gene expression can be down-regulated at the posttranscriptional level by microRNAs (miRNAs), a class of small endogenous RNA. Comparative analysis of miRNA content across species indicates continuous birth and death of these loci in the course of evolution. However, little is known about the microevolutionary dynamics of these genetic elements, especially in plants. In this article we examine polymorphism at two miRNA-encoding loci in Arabidopsis thaliana, miR856 and miR824, which are not found in rice or poplar. We compare their diversity to other miRNA-encoding loci conserved across distant taxa. We find that levels of variation vary significantly across loci and that the two recently derived loci harbor patterns of diversity deviating from neutrality. miRNA miR856 shows a weak signature of a selective sweep whereas miR824 displays signs of balancing selection. A detailed examination of structural variation among alleles found at the miR824-encoding locus suggests nonrandom evolution of a thermoresistant substructure in the precursor. Expression analysis of pre-miR824 and its target, AGL16, indicates that these structural differences likely impact the processing of mature miR824. Our work highlights the relevance of RNA structure in precursor sequence evolution, suggesting that the evolutionary dynamics of miRNA-encoding loci is more complex than suggested by the constraints exerted on the interaction between mature miRNA fragments and their target exon.
Proceedings of the National Academy of Sciences of the United States of America © 2008 National Academy of Sciences