Disruption of Imprinting byMutatorTransposon Insertions in the 5′ Proximal Regions of theZea mays Mez1Locus

Abstract

Imprinting is a form of epigenetic gene regulation in which alleles are differentially regulated according to the parent of origin. The Mez1 gene in maize is imprinted such that the maternal allele is expressed in the endosperm while the paternal allele is not expressed. Three novel Mez1 alleles containing Mutator transposon insertions within the promoter were identified. These mez1-mu alleles do not affect vegetative expression levels or result in morphological phenotypes. However, these alleles can disrupt imprinted expression of Mez1. Maternal inheritance of the mez-m1 or mez1-m4 alleles results in activation of the normally silenced paternal allele of Mez1. Paternal inheritance of the mez1-m2 or mez1-m4 alleles can also result in a loss of silencing of the paternal Mez1 allele. The paternal disruption of imprinting by transposon insertions may reflect a requirement for sequence elements involved in targeting silencing of the paternal allele. The maternal disruption of imprinting by transposon insertions within the Mez1 promoter suggests that maternally produced MEZ1 protein may be involved in silencing of the paternal Mez1 allele. The endosperms with impaired imprinting did not exhibit phenotypic consequences associated with bi-allelic Mez1 expression.

Genomic Distribution of Maize Facultative Heterochromatin Marked by Trimethylation of H3K27

“…Several mu-insertion alleles were obtained via reverse-genetic screening, including mez3-m1, mez3-m4, and mez2-m4 ( Figure 4B). Although Mu insertions were identified in sequences upstream of Mez1 (Haun et al, 2009), we did not find any Mez1 insertions that resulted in lossof-function alleles. Mez2 and Mez3 mutant alleles were backcrossed into B73 for at least seven generations.…”

“…Several putative loss-of-function mu insertion alleles were obtained for mez2 (-m4) and mez3 (-m1 and -m4). No loss-of-function alleles were identified for Mez1 (Haun et al, 2009). The mez2-m4, mez3-m1, and mez3-m4 alleles were backcrossed into B73 for at least seven generations.…”

Combinatorial Networks Regulating Seed Development and Seed Filling

“…Moreover, the mottled phenotype is present regardless of the number of paternal R alleles and maternally inherited R alleles are always associated with the solid red color. Other www.intechopen.com imprinted genes that are maternally expressed in the maize endosperm include the MO17 allele of the dzr1 locus (Chaudhuri & Messing, 1994), one of the -zein alleles (Lund et al, 1995), maize enhancer of Zeste1 gene (Mez1) (Haun et al, 2009) and fertilization independent endosperm1 (Fie1) (Danilevskaya et al, 2003). In Arabidopsis, several imprinted genes involved in early seed development have been identified and include the FIS (FERTILIZATION INDEPENDENT SEED) genes MEDEA (MEA) (Grossniklaus & Schneitz, 1998;Kiyosue et al, 1999), FERTILIZATION INDEPENDENT ENDOSPERM (FIE) (Ohad et al, 1996), FIS2 (Luo et al, 1999), and MULTI-COPY OF IRA1 (MSI1) (Köhler et al, 2003;Ingouff et al, 2007), the MEA homologs CURLY LEAF (CLF) or SWINGER ( SWN) , and other maternally imprinted genes such as MATERNALLY EXPRESSED PAB C-TERMINAL (MPC) (Tiwari et al, 2008) and FLOWERING WAGENINGEN (FWA) (Kinoshita et al, 2004;Köhler & Hennig, 2010 In plants and animals, homeotic genes encoding the polycomb group (PcG) and trithorax group (trxG) proteins are key players in maintaining repressive and active state of targets, respectively, and are crucial for developmental patterning and growth control (Simon & Tamkun, 2002).…”

Genomic imprinting in plant embryos

“…28,31,45,49 For the histone modification H3K9me3 which is typically associated with repression of repetitive elements, 50 no evidence was found for paternal enrichment at imprinted loci in maize endosperm and thus for the involvement in imprinting regulation. The active, maternal alleles were enriched for the active chromatin marking histone modifications H3 and H4 acetylation.…”