AN EXAMINATION OF TISSUE-SPECIFIC PATTERNING SPECIFIED BY A MULTICOPY PERICARP COLOR1 ALLELE IN MAIZE. GET MORE BIOLOGY PROJECT TOPICS AND MATERIALS
Abstract:
The extensive allelic series for the maize <I>pericarp color1</I> (<I>p1</I>) gene is a valuable resource for investigating how sequence and/or structure differences influence tissue-specific gene expression. Previous results showed that the single-copy <I>P1-rr</I> (red pericarp and red cob glumes) allele has considerably less DNA methylation as compared with the six-copy, tandemly-repeated <I>P1-wr</I> (white pericarp and red cob glumes) allele. Herein, the mechanism by which the tandem repeats of <I>P1-wr</I> influence the epigenetic suppression in pericarp tissue was investigated. The disruption of a single <I>P1-wr</I> copy by a <I>Mu1</I> transposon insertion into the 5’UTR induced a gain of pericarp pigmentation in the <I>P1-wr-mum6</I> allele. This gain of pericarp pigmentation was associated with DNA hypomethylation at a distal floral-organ-specific enhancer element. Interestingly, this hypomethylated state led to the expression from wild type copy(s) that were not interrupted by the transposon in the <I>P1-wr</I> mum6 allele. The correlation of copy number and silencing was further strengthened by the characterization of <I>P1-mosaic</I> (<I>P1-mm</I>) which has a <I>P1-wr</I> type gene structure but contains a reduced copy number. <I>P1-mm</I> has both a variegated pericarp pigmentation and a highly perturbed DNA methylation pattern. Interestingly, <I>P1-mm</I> was hypomethylated at the aforementioned distal enhancer and hypermethylated downstream of the transcription start site. These opposing DNA methylation changes are envisaged to explain the unpredictable, mosaic pigmentation pattern of <I>P1-mm</I>. Collectively, the <I>P1-wr-mum6</I> and <I>P1-mm</I> studies showed that the tandem-repeat structure of <I>P1-wr</I> is important for the epigenetic regulation that determines its tissue-specific expression. To further understand why the presence of multiple gene copies is conducive to the suppression of <I>p1</I> in pericarp tissue we studied the dominant <I>Unstable factor for orange1</I> (<I>Ufo1</I>) mutation. The presence of <I>Ufo1</I> induces ectopic pericarp pigmentation in <I>P1-wr</I> plants by a mechanism which correlates with the partial loss of DNA methylation at <I>P1-wr</I>. In addition to endogenous <I>P1-wr</I>, data herein suggests that <I>Ufo1</I> can also reactivate suppressed <I>p1</I> transgenes. Interestingly, although <I>Ufo1</I> has been previously characterized as unstable, its interaction with one <I>p1</I> transgene was highly penetrant and required the continued presence of <I>Ufo1</I>. To identify genes that are important for the range of <I>P1-wr Ufo1</I> expression in pericarp, we crossed a fully-penetrant <I>P1-wr Ufo1</I> stock with RNAi lines that target candidate chromatin-related genes. We found that the Retinoblastoma-associated Protein1 (RBAP1) may function to suppress the <I>Ufo1</I> mutation leading to its variable expression patterns. Collectively, this research broadens the understanding of how tandem repeats of genes influence the epigenetic control of tissue specific expression.
AN EXAMINATION OF TISSUE-SPECIFIC PATTERNING SPECIFIED BY A MULTICOPY PERICARP COLOR1 ALLELE IN MAIZE. GET MORE BIOLOGY PROJECT TOPICS AND MATERIALS
