Research

R. Geeta, Professor, Department of Botany, University of Delhi, Delhi

Biodiversity Studies: Plant Systematics and Evolution

1667DalataMF“Biodiversity” includes the diversity of taxa and their traits. How did this diversity come about? Does the diversity represent a range of “solutions” that deal with the “problem” of living? What are these problems and what are the solutions? Answers to these questions represent understanding of the history of biodiversity.

Understanding this history entails two things: understanding the historical paths of change (what happened, when?) and understanding the underlying processes (what factors are behind such changes?).

My research is focussed on tracing the historical path of biological diversification. My goal is to integrate understanding of multiple processes (developmental, morphogenetic, physiological) at multiple levels (molecular, cellular, organismal) to obtain a comprehensive understanding of evolving biological systems (plants). This work involves the marriage of multiple disciplines, e.g., “traditional” botany and “modern” molecular genetics and, critically, phylogenetics (reconstruction of evolutionary relationships among taxa and using the phylogenetic framework to analyse data from many species). The taxonomic scope of this work includes monocotyledons, DioscoreaCrotalaria and fungi; phylogenetic and developmental studies use both molecular and morphological data. My collaborators and I have studied developmental and evolutionary patterns of variation in characters at different levels of organization: morphological (leaf development and evolution), cellular (reproductive development), subcellular (relocalization of duplicate proteins), genomic (nuclear DNA amount and phenotypic correlates), and molecular (Knox, a homeobox multigene family) and through integrative phylogenetic analyses. Our studies have also extended into evolutionary ecology and historical analysis (presence of Datura in Asia).

Current research in my lab includes investigation of phylogenetic systematics and biochemical, morphological evolution and biogeography in Dioscorea (true yams), floral and fruit evolution in Rhododendron, Justicia, Impatiens and Moringa.

Publications

  • Geeta R, Lohmann LG, Magallón S, Faith DP, Hendry A, Crandall K, De Meester L, Webb C, Prieur-Richard A-H, Mimura M, Conti E, Cracraft J, Forest F, Jaramillo C, Donoghue M and Yahara T. Biodiversity only makes sense in the light of evolution. J. Biosci. 39 doi/10.1007/s12038-014-9427-y. 2014
  • Sharma R, Geeta R, Bhat V. Male/Female gametophyte development in facultative apomictic plants of Cenchrus ciliaris (Poaceae) is asynchronous. S Afr. J. Bot. 91:19-31. 2014.
  • Subramaniam S, Pandey AK, Geeta R, Mort ME. Molecular systematics of Indian Crotalaria (Fabaceae) based on analyses of nuclear ribosomal ITS DNA sequences. Plant Systematics and Evolution. DOI 10.1007/s00606=013-0781-2. 2013.
  • Geeta R, Davalos LM, Levy A. et al. Keeping it simple: flowering plants tend to retain, and revert to, simple leaves. New Phytologist 193: 481-493. DOI: 10.1111/j.1469-8137.2011.03951.x 2012
  • Vencl F, Trillo P, Geeta R. Functional interactions among tortoise beetle larval defenses reveal trait suites and escalation. Behav Ecol Sociobiol 64: DOI 10.1007/s00265-010-1031-z. 2010.
  • Mignouna H, Abang MM, Asiedu R and Geeta R. Dioscorea, true yams – A biological and evolutionary link between eudicots and grasses. In Emerging Model Organisms. Cold Spring Harbor Laboratory Press. doi:10.1101/pdb.emo136. 2009.
  • Geeta R and Gharaibeh W. Historical evidence for a pre-Columbian presence of Datura in the Old World and implications for a first millenium transfer from the New World. J. Biosci. 32: 1227-1244. 2007.
  • Champagne CEM, Goliber TE, Wojciechowski MF, Mei RW, Townsley BT, Wang K, Paz MW, Geeta R and Sinha NR. 2007. Compound Leaf Development and Evolution in the Legumes. Plant Cell 19 3369-3378. 2007
  • Byun-McKay SA and Geeta R. Protein subcellular relocalization: a new perspective on the origin of novel genes. Trends Ecol. Evol. 22:338-344. 2007.
  • Tellez VO and Geeta R. Dioscorea howardiana, a new species in section Trigonobasis (Dioscoreaceae). Brittonia 59: 370-373. 2007.
  • Murali TS, Suryanarayanan TS, Geeta R. Endophytic Phomopsis species: host range and implications for diversity estimates. Can J. Microbiol 52: 673-680. 2006.
  • Geeta R. Structure trees, species trees: What they say about morphological development and evolution. Evol. Dev. 5: 609-621. 2003.
  • Geeta R. Variation and diversification in plant evo-devo (book review). Amer. J. Bot. 90: 1257-1261. 2003.
  • Geeta R. The origin and maintenance of nuclear endosperms: Viewing development through a phylogenetic lens. Proc. R. Soc. B. 270: 29-35. 2003.
  • Hjortswang HI, Larsson AS, Bharathan G, Bozhkov PV, Von Arnold S, and Vahala T KNOTTED1-like homeobox genes of a gymnosperm, Norway spruce, expressed during somatic embryogenesis. Plant Physiol. Biochem. 40: 837-843. 2002.
  • Bharathan G, Goliber T, Moore C, Kessler S, Pham T and Sinha N. Homologies in leaf development inferred from KNOXI gene expression. Science 296: 1858-1860. 2002.
  • Bharathan G and Sinha NR. The Regulation of Compound Leaf Development. Plant Physiol. 127: 1533-1538. 2001.
  • Bharathan G, Janssen B-J, Kellogg EA, and Sinha N. Phylogenetic relationships and evolution of the KNOTTED class of plant homeodomain proteins. Mol. Biol. Evol. 16: 553-563. 1999.
  • Goliber T, Kessler S, Chen J-J, Bharathan G, and Sinha N. Genetic, molecular, and morphological analysis of compound leaf development. Invited review in R. A. Pederson and G. Schatten [ed.]. Current Topics in Developmental Biology, Vol 43:259-290. Academic Press. 1998.
  • Bharathan G, Janssen B.-J, Kellogg EA, and Sinha N. Did homeodomain proteins duplicate before the origin of angiosperms, fungi , and metazoa? Proc. Natl. Acad. Sci. 94:13749-13753. 1997.
  • Bharathan G. Does the monocot mode of leaf development characterize all monocots?” Aliso 14:271-279. 1996.
  • Bharathan G. “Reproductive development and nuclear DNA content in angiosperms. Amer. J. Bot. 83:440-451. 1996.
  • Bharathan G and Zimmer EA. Early branching events in monocotyledons — partial 18S ribosomal DNA sequence analysis. In P. J. Rudall, P. J. Cribb, D. F. Cutler and C. J. Humphries [ed.], Monocotyledons — systematics and evolution, Vol. I, 81-108. Royal Botanic Gardens, Kew. 1995.
  • Bharathan G, Lambert G, and Galbraith DW. Nuclear DNA content of monocotyledons and related taxa. Amer. J. Bot. 81:381-386. 1994.
  • Sanderson MJ, Baldwin BG, Bharathan G, Campbell CS, von Dohlen C, Ferguson D, Porter JM, Wojciechowski MF, and Donoghue MJ. The growth of phylogenetic information, and the need for a phylogenetic data base. Syst. Biol. 42:562-568. 1993.
  • Sanderson MJ and Bharathan G. Does cladistic information affect inferences about branching rates? Syst. Biol. 42:1-17. 1993.

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