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United States Department of Agriculture

Agricultural Research Service

Title: Multiple Ribosomal Rna Gene Loci in the Genome of the Homosporous Fern

Authors
item McGrath, J Mitchell
item Hickok, L - UNIVERSITY OF TENNESSEE

Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 25, 1999
Publication Date: N/A

Interpretive Summary: Ferns are among the first land plants to appear in the fossil record. The genes in ferns have not received much attention by scientists despite their use in understanding genes in crop plants. Comparison of gene structure and function between ferns and crop plants, whose geological histories are very different, should show how these genes have evolved from a common ancestor. .Natural mechanisms of genetic change in crop plants are now being understood, but they are not necessarily ones that ferns have followed. A highly conserved family of genes that is well understood in crop plants was applied to ferns. An experiment was designed to ask the question: what is the fate of these genes in an ancient fern lineage relative to a recent crop lineage? Results showed that the number of genes was similar in ferns and crops, implying that gene function and not evolutionary history is important to retain gene function. This suggests that insight into gene structure and function can be gained by the study of ferns, and this insight can be used to compare crop and fern genes for conserved regions of genes that retain vital functions. Scientists will be able to use this information to develop a model to better understand genetic change over very long periods of time. In turn, this new knowledge will aid plant breeders in understanding which genes and parts of genes are essential to crop growth and economic productivity. Information of this kind is essential for the development of more efficient plant selections and breeding strategies for crop improvement.

Technical Abstract: The genomes of homosporous ferns are largely uncharacterized, but they appear to differ from gymnosperms and angiosperms in key aspects, such as high chromosome numbers at the diploid level, and thus provide a unique perspective on plant genome structure and evolution. The homosporous fern, ceratopteris richardii, was the model used in the study. Loci encoding ribosomal RNA sequences (rDNA genes) were detected using fluorescent in situ hybridization. At least two major rDNA loci were visible in all cases, and six or more weakly hybridizing signals were observed in most cytological preparations. These results are consistent with models of homosporous fern evolution via cycles of polyploidy followed by gene silencing. They are also consistent with other models of fern genome evolution. With the exception of the weakly hybridizing signals, these data are similar to analogous reports of one or two major rDNA loci in diploid angiosperms. These results suggest that the gross morphology of rDNA loci are similar between diploid homosporous ferns and angiosperms, but that important clues to rDNA gene and chromosome evolution in homosporous ferns may reside in the analysis of their minor rDNA sequences.

Last Modified: 10/22/2014
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