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Paula McSteen

Paula McSteen

Professor of Biological Sciences

Biological Sciences,


Research summary

Genetic regulation of meristem function in plants

Research description

POSITIONS AVAILABLE: Postdoctoral scholar and graduate student positions available now. Full time undergraduate student positions available during the summer. Email resume to

Unlike animals, which make organs only during embryogenesis, plants make organs throughout their lifetime through the action of specialized groups of cells called meristems. Meristems function by setting aside groups of cells to become organ primordia while maintaining a population of undifferentiated cells to support further growth. My lab focuses on axillary meristems, which give rise to branches and flowers and therefore play a fundamental role in plant architecture and reproduction. The goal of our research is to understand how the hormonal signal for axillary meristem initiation is perceived and transmitted to cause the changes in gene expression, cell division and expansion required for the formation of an axillary meristem.

Using a genetic approach, we have identified many mutants with defects in the development of axillary meristems in the maize inflorescence. Characterization of each mutant tells us the biological function of the gene that has been disrupted. Identification of the corresponding gene by positional cloning enables us to determine its mechanism of action using molecular, biochemical and cell biology approaches. Many of the genes defective in these mutants regulate the transport, biosynthesis or signaling of the plant growth hormone auxin, illustrating the importance of this hormone in the process of axillary meristem and organ initiation.

One of the projects we are working on involves the barren inflorescence2 (bif2) mutant, which makes fewer branches and flowers due to defects in the initiation and growth of axillary meristems. bif2 encodes a serine threonine protein kinase expressed in axillary meristems and organ primordia. BIF2 regulates auxin transport by phosphorylating ZmPIN1a, which encodes an auxin efflux transporter. BIF2 also interacts with and phosphorylates BARREN STALK1 (BA1), a bHLH transcription factor that plays an important role in axillary meristem formation. Another project involves the sparse inflorescence1 (spi1) mutant which has a similar phenotype to bif2 in the inflorescence. spi1 encodes an enzyme involved in localized auxin biosynthesis showing that both local synthesis and transport of auxin are required for axillary meristem initiation in the inflorescence. spi1; bif2 double mutants have very severe effects on vegetative development indicating that auxin transport and biosynthesis also play an important role in vegetative development.

Current research uses genetic, genomic, molecular, biochemical, cell biology and physiological approaches to understand the gene regulatory network controlling auxin mediated development in the maize inflorescence. We are currently characterizing and cloning many new mutants with defects similar to spi1 and bif2 as part of an NSF Plant Genome project. See project website Through comparison of the role of these genes in maize versus other plant species we are developing an understanding of the evolution of the role of auxin in plant development.

Select Publications

Pike, S., Matthes, M.S., McSteen, P., Gassmann, W. Using Xenopus laevis Oocytes to Functionally Characterize Plant Transporters (2019) Current protocols in plant biology, 4 (1), p. e20087. DOI: 10.1002/cppb.20087

Yao, H., Skirpan, A., Wardell, B., Matthes, M.S., Best, N.B., McCubbin, T., Durbak, A., Smith, T., Malcomber, S., McSteen, P. The barren stalk2 Gene Is Required for Axillary Meristem Development in Maize (2019) Molecular Plant, 12 (3), pp. 374-389. DOI: 10.1016/j.molp.2018.12.024

Matthes, M.S., Best, N.B., Robil, J.M., Malcomber, S., Gallavotti, A., McSteen, P. Auxin EvoDevo: Conservation and Diversification of Genes Regulating Auxin Biosynthesis, Transport, and Signaling (2019) Molecular Plant, 12 (3), pp. 298-320. DOI: 10.1016/j.molp.2018.12.012

Matthes, M.S., Robil, J.M., Tran, T., Kimble, A., McSteen, P. Increased transpiration is correlated with reduced boron deficiency symptoms in the maize tassel-less1 mutant (2018) Physiologia Plantarum, 163 (3), pp. 344-355. DOI: 10.1111/ppl.12717

A. Durbak, K. Phillips, S. Pike, M. O’Neill, J. Mares, S. Malcomber, A. Gallavotti, W. Gassmann, and P. McSteen (2014). Transport of boron by the tassel less1 aquaporin is critical for vegetative and reproductive development in maize. Plant Cell 26: 2978-2995.

P. McSteen, B. Scheres, and Y. Zhao (2013) Preface. Journal of Experimental Botany, 64(9):2539-2540.

A. Durbak, H. Yao, and P. McSteen (2012) Hormone signaling in plant development. Current Opinion in Plant Biology, 15: 92-96

K.A. Phillips, A.L. Skirpan, X. Liu, A. Christensen, T.L. Slewinski, C. Hudson, S. Barazesh, J.D. Cohen, S. Malcomber and P. McSteen (2011) vanishing tassel2 encodes a grass-specific tryptophan aminotransferase required for vegetative and reproductive development in maize. Plant Cell, 23:550-566.

K. Mashiguchi, K. Tanaka, T. Sakai, S. Sugawara, H. Kawaide, M. Natsume, A. Hanada, T. Yaeno, K. Shirasu, H. Yao, P. McSteen, Y. Zhao, K. Hayashi, Y. Kamiya, and H. Kasahara (2011) The main auxin biosynthesis pathway in Arabidopsis. Proceedings of the National Academy of Sciences USA, 108: 18512-18517.

P. McSteen (2010) Auxin and Monocot Development. Cold Spring Harbor Perspectives in Biology. 2:a001479.

J.B. Woodward, N.D. Abeydeera, D. Paul, K. Phillips, M. Rapala-Kozik, M. Freeling, T.P. Begley, S.E. Ealick, P. McSteen, M.J. Scanlon (2010) A maize thiamine auxotroph is defective in shoot meristem maintenance. Plant Cell, 22: 3305-3317.

P. McSteen (2009) Hormonal regulation of branching in grasses. Plant Physiology, 149: 46-55.

A. Skirpan, A. Hendrickson Culler, A. Gallavotti, D. Jackson, J.D. Cohen and P. McSteen (2009) BARREN INFLORESCENCE2 interaction with ZmPIN1a suggests a role in auxin transport during maize inflorescence development. Plant & Cell Physiology, 50: 652-657.

S. Barazesh, C. Nowbakht, and P. McSteen (2009) sparse inflorescence1, barren inflorescence1 and barren stalk1 promote cell elongation in maize inflorescence development. Genetics, 182: 403–406.

X. Wu, A. Skirpan and P. McSteen (2009) Suppressor of sessile spikelets1 functions in the ramosa pathway controlling meristem determinacy in maize. Plant Physiology, 149: 205-219.

K. Phillips, A. Skirpan, N. Kaplinsky and P. McSteen (2009) Developmental Disaster1: A novel mutation causing defects during vegetative and inflorescence development in maize (Zea mays, Poaceae). American Journal of Botany, 96: 420-430.

S. Barazesh and P. McSteen (2008) Hormonal control of grass inflorescence development. Trends in Plant Sciences, 13:656-662.

A. Gallavotti, S. Barazesh, S. Malcomber, D. Hall, D. Jackson, R.J. Schmidt, P. McSteen (2008) sparse inflorescence1 encodes a monocot-specific YUCCA-like gene required for vegetative and reproductive development in maize. Proceedings of the National Academy of Sciences USA, 105:15196-15201.

A. Skirpan, X. Wu and P. McSteen (2008) Genetic and physical interaction suggest that BARREN STALK1 is a target of BARREN INFLORESCENCE2 in maize inflorescence development. The Plant Journal, 55:787-797.

S. Barazesh and P. McSteen (2008) barren inflorescence1 functions in organogenesis during vegetative and inflorescence development in maize. Genetics, 179:389-401.

P. McSteen and Y. Zhao (2008) Plant hormones and signaling: common themes and new developments. Developmental Cell, 14:467-473.

X. Wu and P. McSteen (2007) The role of auxin transport during inflorescence development in maize, Zea mays (Poaceae). American Journal of Botany, 94:1745-1755.

P. McSteen, S. Malcomber, A. Skirpan, C. Lunde, X. Wu, E. Kellogg and S. Hake (2007) barren inflorescence2 encodes a co-ortholog of the PINOID serine/threonine kinase and is required for organogenesis during inflorescence and vegetative development in maize. Plant Physiology, 144:1000-1011.

P. McSteen (2006) Branching out: The ramosa pathway and the evolution of grass inflorescence morphology. Plant Cell, 18:518-522.

P. McSteen and O. Leyser (2005) Shoot branching. Annual Review of Plant Biology, 56:353-74.

Selected honors and awards

Outstanding Undergraduate Research Mentor/Research Mentor of the Year Award 2019

Mid-Career Excellence in Maize Genetics Award 2016