Jay B Hollick

Associate Adjunct Professor
Ph.D.  Biochemistry    University of Washington, Seattle, 1993
B.A.   Genetics    University of California, Berkeley, 1988

561 Life Sciences Addition
Berkeley, California 94720
hollick@berkeley.edu
office: 510-643-1734   lab: 510-643-1734   fax:  510-642-0355

     Recent publications      People

We are interested in mechanisms that generate and maintain heritable phenotypic variation. Our current emphasis is aimed at understanding epigenetic systems that cause mitotically, and meiotically, heritable changes in gene activity. We are focusing on one particular mechanism, called paramutation, in which the regulation of one allele is heritably altered through interactions with the homologous allele. We are asking several key questions: what is the molecular nature of this meiotically heritable change, how does this change affect gene expression, how do two alleles communicate with each other, and how general is this mechanism in plant growth and development? We use the superb genetic, molecular genetic, cytogenetic, and cytological tools available in Zea mays to address these questions.

Our general strategy is to identify molecular and cellular components required for paramutation and then use these as tools to further understand the genomic and chromosome dynamics involved. We use the well-defined anthocyanin pigment pathway as our simple model system. Plant color in maize is quantitatively controlled by action of the purple plant1 (pl1) gene. One particular pl1 allele (Pl) can exist in distinct transcription states. In the figure to the right, note tassels of sibling maize plants displaying two distinct epigenetic expression states of the pl1 gene. Darkly colored anthers reflect high levels of pl1 transcription and lightly colored anthers indicate a repressed transcription state.

Highly transcribed Pl alleles are invariably repressed when exposed to a repressed Pl allele (Pl’) in a heterozygote. Genetic and molecular observations suggest that paramutation reflects alterations in chromatin structure that are sensitive to chromosome pairing interactions.

We’ve begun to identify important components of the paramutation system using genetic analyses. Seedling-based screens have identified mutations in critical cis-acting sequences and a novel class of trans-acting rmr (required to maintain repression) loci that allow heritable restoration of high levels of pl1 gene action. Several rmr genes also play crucial roles in growth and development. Cloning of these rmr loci by positional approaches has begun to highlight novel features of a presumed small RNA-directed DNA methylation pathway that affect meiotically heritable changes in epigenomic control. In addition to cloning the remaining rmr genes, we are currently taking both biochemical and genomic approaches to understand the operation of this novel regulatory system in plant development and homeostasis.

Stonaker, J.L., Lim, J.P., Erhard, K.F., Hollick, J.B. 2009 Diversity of Pol IV function is defined by mutations at the maize rmr7 locus. PLoS Genetics 5(8): e1000706. doi:10.1371/journal.pgen.1000706 PDF 323 kb

Hale, C.J., Erhard, K.F., Lisch, D., Hollick, J.B. 2009 Production and processing of siRNA precursor transcripts from the highly repetitive maize genome. PLoS Genetics 5(8): e1000598. doi:10.1371/journal.pgen.1000598 PDF 1434 kb

Erhard, K.F. Jr., Stonaker, J.L., Parkinson, S.E., Lim, J.P., Hale, C.J., Hollick, J.B. (2009) RNA Polymerase IV functions in paramutation in Zea mays. Science 323: 1201-1205.

Hollick, J.B., (2008) Sensing the epigenome. Trends in Plant Sci. 13(7): 398-404. PDF 339 kb

Hale, C.J., Stonaker, J.L., Gross, S.M. and Hollick, J.B. (2007) A novel Snf2 protein maintains trans-generational regulatory states established by paramutation in maize. PLoS Biol 5(10): 2156-2165 e275. PDF 663 kb

Parkinson, S.E., Gross, S.M. ad Hollick, J.B. (2007) Maize sex determination and abaxial leaf fates are canalized by a factor that maintains repressed epigenetic states. Dev Biol 308: 462-473. PDF 1739 kb

Gross, S.M and Hollick, J.B. (2007) Multiple trans-sensing interactions affect meiotically heritable epigenetic states at the pl1 locus. Genetics 176: 829-839. PDF 1199 kb

Hollick, J.B., Kermicle, J.L. and Parkinson, S.E. (2005) Rmr6 maintains meiotic inheritance of paramutant states in Zea Mays. Genetics 171: 725-740. PDF 386 kb

Hollick, J.B. (2003) Paramutation in Plants. Encyclopedia of Life Sciences. April 2003. PDF 1334 kb

Hollick, J.B. and Chandler, V.L. (2001) Genetic factors required to maintain repression of a paramutagenic maize pl1 allele. Genetics 157: 369-378. PDF 310 kb

Dorweiler, J.D., Carey, C.C., Kubo, K.M., Hollick, J.B., Kermicle, J., Chandler, V.L. (2000) Mediator of paramutation 1 is required for the establishment and maintenance of paramutation at multiple maize loci. The Plant Cell 12 (11): 2101-2118. PDF 467 kb

Hollick, J.B., Patterson, G.I, Asmundsson, I.M., Chandler, V.L. (2000) Paramutation alters regulatory control of the maize pl locus. Genetics 154: 1827-1838. PDF 342 kb

Hollick, J.B. and Chandler, V.L. (1998) Epigenetic allelic states of a transcriptional regulatory locus exhibit overdominant gene action. Genetics 150: 891-897.

Hollick, J.B., Dorweiler, J.E., Chandler, V.L. (1997) Paramutation and related allelic interactions. Trends in Genetics 13 (8): 302-307.

Chandler, V.L., Kubo, K.M., Hollick, J.B. (1996) b and pl paramutation in maize: heritable transcription states programmed during development, In Epigenetics. R. Martienssen, A. Riggs, and V.E.A. Russo eds., Cold Spring Harbor Press, pp 289-304.

Hollick, J.B., Patterson, G.I., Coe, E.H., Cone, K.C., Chandler V.L. (1995) Allelic interactions heritably alter the activity of a metastable maize pl allele. Genetics 141: 709-719