Robert L. Fischer
University of California, Berkeley
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Primary Section: 62, Plant, Soil, and Microbial Sciences Secondary Section: 25, Plant Biology Membership Type:
Member
(elected 2009)
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Research Interests
I have studied the mechanisms that regulate gene imprinting in plants, which causes unequal expression of maternal-derived and paternal-derived alleles and is required for plant reproduction. Plant imprinted genes are expressed in the endosperm, a placenta-like tissue that supports the growth and development of the embryo. The endosperm tissue develops from a fertilized maternal central cell and is the primary source of carbon, nitrogen, and energy for humans and domesticated animals. My laboratory discovered that DNA demethylation in the central cell underlies gene imprinting in Arabidopsis. Maternal alleles in the central cell are demethylated by the base excision DNA repair pathway. A DNA glycosylase, DME, initiates DNA demethylation by excising 5-methylcytosine, which is replaced with cytosine by DNA polymerase. Because DNA demethylation occurs before fertilization the central cell and not in sperm, imprinted alleles are epigenetically marked depending on their parent-of-origin; maternal alleles are demethylated and transcriptionally active, whereas paternal alleles are methylated and silenced. DNA demethylation in the central cell activates expression of maternal Polycomb group proteins that, in turn, imprint and silence additional genes by histone methylation. Thus, multiple epigenetic mechanisms in the central cell program gene imprinting in the endosperm. More recently, I have been studying the epigenetic regulation of imprinting at the genome-wide level and find that DNA demethylation extensively reconfigures the endosperm methylation landscape.
