American Society of Plant Biologists 
CONTACT US     SITE MAP     SEARCH     PRIVACY POLICY     ADVERTISE  
Abstract Center . Session List .
Search:
Minisymposium 12: Genome evolution

Abs # 25002: A possible role for large-scale RNA-mediated gene duplication in the evolution of a huge plant superfamily

Presenter: Vernon, Daniel M, vernondm@whitman.edu
AuthorsAnderson, Tovi M (A)   Hutchison, Delbert  (B)   Vernon, Daniel M (B) (A) 
Affiliations: (A): Program In Biochemistry, Biophysics, and Molecular Biology, Whitman College, Walla Walla, WA, 99362
(B): Biology Department, Whitman College

Pentatricopeptide Repeat proteins (PPRs) function in organelle RNA processing and translational control, and probably other cellular & developmental processes. The PPR domain in these proteins is thought to form a nucleic-acid binding structure. PPRs are found in all eukaryotes but the superfamily is greatly expanded in plants, with more than 400 members in the Arabidopsis genome. To investigate the dramatic evolutionary expansion of PPRs in plants, we have characterized the structure & chromosomal distribution of 439 Arabidopsis PPR genes, comparing them to two control groups: the similarly large LRR-RLK family and a set of 50 randomly selected loci encoding products of comparable size. PPR genes had a number of unusual features. They had significantly fewer introns (median=0) than genes in either control group, with >67% of PPRs having no introns. Also, PPR genes were statistically significantly closer to adjacent loci than control group genes were to their nearest neighbors (mean distance = 454 bp), with many being less than 50 bp from adjacent genes. Both of these characteristics are consistent with a model in which PPRs expanded via RNA intermediates. To further examine this possibility, we investigated the chromosomal geography of PPRs, comparing it to that of large gene families that arose through DNA-mediated (chromosomal) mechanisms- LRR-RLKs and NBS-LRR pathogen resistance genes. The distribution of PPR s differed from that of these comparison groups: PPRs were distributed throughout the genome and were not found in large clusters or tandem arrays. Also, pairs of closely-related PPR genes were not found in corresponding duplicated chromosomal blocks. Thus, much PPR gene expansion apparently occurred independent of chromosomal segmental duplication events. We propose that the PPR superfamily grew in part by reverse-transcription of spliced ancestral RNAs, followed by insertion into active chromosomal regions. This model accounts for the superfamily's characteristics: large numbers of scattered, intronless genes situated very close to neighboring transcription units. While RNA-mediated duplication has been a major force in the expansion of non-coding elements in eukaryotic genomes, and has led to individual gene duplications, PPRs may provide the first example of large-scale RNA-mediated gene superfamily expansion in plants. Supported in part by USDA award 02-35304-12304 to DMV

Abstract Center . Session List .
Search: