Poster: Posttranscriptional Regulation

Abs # 1077: Overlapping genes and organ-specific aberrant splicing at the Arabidopsis PIRL6 locus

Presenter:	Forsthoefel, Nancy , Forsthn@Whitman.edu
Authors	Forsthoefel, Nancy  (A)   Cutler, Kerry  (A)   Vernon, Daniel M (A)
Affiliations:	(A): Whitman College

Plant Intracellular Ras-group LRR proteins (PIRLs) constitute a novel class of leucine-rich repeat proteins structurally related to a class of signal transduction LRRs from animals & fungi. We are carrying out a structural & reverse-genetic study of the 9 Arabidopsis PIRL genes (formerly called SLATs). Here we report the unusual complexity of one, PIRL6. The predicted gene structure, like related PIRLs, consists of 3 exons with 2 introns at conserved positions. Interestingly, the 3'-end of PIRL6 substantially overlaps an unrelated transcription unit on the opposite strand of chromosome 2. This overlap has muddled database annotations of both genes. RT-PCR indicated that the predicted PIRL6 mRNA is expressed in leaves, roots, flowers, & siliques.. Leaves, roots, & siliques yielded additional RT-PCR products. Cloning & sequencing of 8 cDNAs from leaves defined 3 other PIRL6 RNA species with alternative structures in the 5' half of the gene. All contained 8bp of intron 1 and lacked 5' portions of exon 2. Two of the cDNAs also contained the second intron, unspliced. None contained extended ORFs on either strand. Abnormal PIRL6 cDNAs were not detected in flowers, and no abnormal transcripts have been detected for any other PIRL genes. We propose that these cDNAs represent stable, incorrectly-spliced PIRL6 transcripts. Alternatively, they could originate from a cryptic opposite-stand transcription unit, raising the possibility that the PIRL6 region actually encompasses 3 overlapping genes that produce 5 different transcripts. These results illustrate Arabidopsis' potential for gene complexity & underscore the hypothetical nature of current annotation. Progress towards defining transcriptional complexity of this locus will be presented. Supported by the Murdock Trust & USDA