Phone: (650) 739-4283 Fax: (650) 325-6857 Links to Specific Research ProjectsRegulation of gamete number and embryo sac cell identityMaternal Regulation of Seed DevelopmentCross-incompatibility between maize and wild teosinteFunctional Genomics of GametogenesisLab TabsOur ResearchPublications Maize Reproductive Development Figure 1. Angiosperm life cycle. The plant life cycle alternates between a diploid sporophyte and a haploid gametophyte generation (Figure 1). Specialized cells of the diploid sporophyte undergo meiosis to produce male or female spores. The sexually dimorphic spores divide to develop into haploid organisms, the gametophytes, which produce the gametes--the sperm and egg cells. In flowering plants, the female gametophyte, called the embryo sac, consists of four cell types: the egg cell, the central cell, the synergids, and the antipodal cells (Figure 2). The male gametophyte (the pollen grain) contains a vegetative cell, which performs the metabolic functions of the pollen grain and delivers the gametes to the embryo sac, and two sperm cells that fertilize the egg and central cell to produce the embryo and endosperm, respectively. The embryo develops into a new plant to continue the life cycle. The endosperm produces the nutritive material used by the embryo and seedling and comprises the bulk of the grain weight in cereals such as wheat, rice, and maize. The embryo and endosperm together make up the seed. The gametophytes of plants have active haploid genomes, in contrast to animals, where the products of meiosis are genetically inactive. Figure 2. Male and female gametophyte development. a=antipodal cells; cc=central cell; pn=polar nuclei; e=egg cell; sy=synergid; end=endosperm; emb=embryo; vn= vegetative cell nucleus; v= vegetative cell; va=vacuole gc=generative cell; sp=sperm cells; pt=pollen tube. FG1-FG8=female gametophyte stage 1 to 8. FM=free microspore; VM=vacuolated microspore; BC=bicellular pollen; MP=mature pollen; GP=germinating pollen; dm=degenerated microspores. Maize, like the majority of Angiosperm species, undergoes the Polygonum type of embryo sac development. Three of the spores produced by meiosis abort, and the chalazal most megaspore undergoes three rounds of free nuclear division to produce an eight nucleate syncytium. Cellularization produces a seven-celled embryo sac consisting of: two synergids, which attract the male gametophyte; the egg cell; the homodiploid central cell; and three antipodal cells (Figure 3). In maize the antipodal cells persist and continue to divide. Figure 3. Maize embryo sac. Confocal image of cellularized embryo sac. The embryo sac is imbedded within the nucellus (n) of the ovule. Antipodal cells (a) have already divided a few times. The egg (e) and one of the synergids (s) are in the plane of focus. The synergid has not yet degenerated. The central cell has a large vacuole and two polar nuclei adjacent to the egg. The male gametophyte undergoes one round of division to produce the vegetative cell and the generative cell. The generative cell undergoes a second round of division to produce the two sperm cells, which are both contained within the cytoplasm of the vegetative cell. Upon interaction between the pollen grain and the female stigma, the pollen grain germinates and the vegetative cell produces a pollen tube that grows through the style and is guided to a synergid of the embryo sac. Interaction with the synergid causes pollen tube rupture and release of the two sperm cells, which then fuse with the egg and central cell to achieve fertilization. Fertilization of the embryo sac leads to rapid development of the embryo and endosperm. By four days after pollination (DAP) a small proembryo of approximately 24 cells has formed consisting of the large basal cells of the suspensor and the smaller apical cells of the embryo proper. By eight DAP the embryo has entered the transition stage with a long suspensor and a globular embryo proper. The scutellum (cotyledon) enlarges rapidly after the transition stage, and the coleoptile and shoot apical meristem (SAM) form on the face of the scutellum by approximately 10 DAP. Maize endosperm development begins rapidly after fertilization in comparison to the embryo (Figure 4). It begins with a period of free nuclear divisions to produce a syncytium of over 250 nuclei located at the periphery of the cell. This period is followed by cellularization at approximately three to four DAP, when the embryo is still in the proembryo phase. The endosperm differentiates into at least four distinct domains: the aleurone, the basal endosperm transfer layer (BETL), the starchy endosperm, and the embryo surrounding region (ESR). Figure 4. Endosperm development in maize. The growth of the embryo (gray) is shown for comparison. A syncytial phase is followed by cellularization. A phase of mitotic growth is followed by cycles of endoreduplication and eventually programmed cell death. Blue indicates cells that have undergone programmed cell death. Lab PI Matt Evans Research Staff Scientist Plant BiologyCarnegie Institution for Science email@example.com 650-739-4283 Office: 260 Panama StreetStanford, CA 94305, US  ProfileAffiliationCarnegie Affiliation: DPB EmployeesDPB Affiliation: DPB FacultyLabs: Evans Lab Calendar Lab Members Samuel Hokin (Senior Computational Scientist)Sam received his Ph.D. in plasma physics from MIT, did his post-doc at the Kurchatov Institute in Moscow, and spent the first 10 years of his career on the faculty of the UW-Madison and then KTH in Stockholm. His middle career was in web development, at a small business that he still co-owns in Madison. His third career started when Kathy Barton hired him to analyze a bunch of RNA-seq data in January, 2013. At Carnegie, Sam works on modeling transcription factor regulatory networks in the Barton Lab, and does various bioinformatics tasks in the Evans Lab and anyone else that would like some help. He is 50% at Carnegie DPB and 50% at NCGR in Santa Fe, where he lives. At NCGR, he works on data warehouse software and is delving into the genomic signatures of human diseases. Yongxian Lu (Postdoctoral Associate) Hannah Vahldick (Technician) PublicationsChettoor, A. M., Yang, B., and Evans, M. M. S. Loss of a MAP65-3 blocks cellularization of the embryo sac and proliferation of the antipodal cells in maize. In preparation. Han, L., Li, L., Muehlbauer, G. J., Fowler, J. E., and Evans, M. M. S. RNA isolation and analysis of lncRNAs from gametophytes of maize. In, Methods in Molecular Biology, Plant Long Non-Coding RNAs: Methods and Protocols, J.A. Chekanova, ed., accepted. Chettoor, A. M., and Evans, M. M. S. (2017) Imaging of auxin and cytokinin signaling in the maize female gametophyte. In, Methods in Molecular Biology, vol.1669, Plant Germline Development: Methods and Protocols, A. Schmidt, ed. In press. Vollbrecht, E. and Evans, M. M. S. (2017) Gametophyte interactions establishing maize kernel development. In, Maize Kernel Development, B. Larkins, ed. (Boston: CAB International), pp. 16-27. In press. Chettoor, A. M., Phillips, A. R., Coker, C. T., Dilkes, B. and Evans, M. M. S. (2016) Maternal Gametophyte Effects on Seed Development in Maize. Genetics 204: 233-248. Bai, F., M. Daliberti, A. Bagadion, M. Xu, Y. Li, Baier, J., Tseung, C. W., Evans, M. M.S., Settles, A. M., (2016) Parent-of-Origin-Effect rough endosperm Mutants in Maize. Genetics 204: 221-231. Chettoor AM, Evans MM. Correlation between a loss of auxin signaling and a loss of proliferation in maize antipodal cells. Front Plant Sci. 2015;6:187. link Chettoor AM, Givan SA, Evans MM, Cole RA, et al. Discovery of novel transcripts and gametophytic functions via RNA-seq analysis of maize gametophytic transcriptomes. Genome Biol. 2014;15(7):414. link Li L, Eichten SR, Evans MM, Shimizu R, et al. Genome-wide discovery and characterization of maize long non-coding RNAs. Genome Biol. 2014;15(2):R40. link Lu Y, Kermicle JL, Evans MM. Genetic and cellular analysis of cross-incompatibility in Zea mays. Plant Reprod. 2014;27(1):19-29. link Phillips, A. R. and Evans, M. M. S. (2011). Analysis of stunter1, a Maize Mutant with Reduced Gametophyte Size and Maternal Effects on Seed Development. Genetics, published ahead of print 10.1534/genetics.110.125286. Kermicle, J. L. and Evans, M. M. S. (2010) The Zea mays Sexual Compatibility Gene ga2: Naturally-occurring Alleles, their Distribution and Role in Reproductive Isolation. J. Hered 101: 737-749. http://jhered.oxfordjournals.org/content/101/6/737.full Evans, M. M. S. and Grossniklaus, U. (2009) The maize megagametophyte. In Handbook of Maize: its Biology, J.L. Bennetzen and S. Hake, eds (New York: Springer), pp. 79-104. http://www.springerlink.com/content/978-0-387-79417-4#section=127544&page=1&locus=0 Wenkel, S., Emery, J., Hou, B.-H., Evans, M. M. S., and Barton, M.K. (2007) A Feedback Regulatory Module Formed by LITTLE ZIPPER and HD-ZIPIII Genes. Plant Cell 19: 3379-3390.link Evans, M. M. S. (2007) The indeterminate gametophyte1 gene of maize encodes a LOB domain protein required for embryo sac and leaf development. Plant Cell 19: 46-62.link Gutierrez-Marcos, J. F., Costa, L. M., and Evans, M. M. S. (2006) Maternal gametophytic baseless1 is required for development of the central cell and early endosperm patterning in maize (Zea mays). Genetics 174: 317-329.link Kermicle, J. L., Taba, S., and Evans, M. M. S. (2006) The gametophyte-1 locus and reproductive isolation among Zea mays subspecies. Maydica, 51: 219-225. link Kermicle, J. L. and Evans, M. M. S. (2005) Pollen-pistil barriers to crossing in maize and teosinte result from incongruity rather than active rejection. Sex. Plant Reprod. 18: 187-194.link Walbot, V. and Evans, M. M. S. (2003) Unique features of the plant life cycle and their consequences. Nature Rev. Genet. 4: 369-379.link Evans, M. M. S. and Kermicle, J. L. (2001) Interaction between maternal effect and zygotic effect mutations during maize seed development. Genetics 159: 303-315.link Evans, M. M. S. and Kermicle, J. L. (2001) Teosinte crossing barrier1, a locus governing hybridization of teosinte with maize. Theor. Appl. Genet. 103: 259-265.link Evans, M. M. S. and Barton, M. K. (1997) Genetics of angiosperm shoot apical meristem development. Ann. Rev. Plant Physiol. and Plant Mol. Biol. 48: 673-701. Evans, M. M. S. and Poethig, R. S. (1997) The viviparous8 mutation delays vegetative phase change and accelerates the rate of seedling growth in maize. Plant Journal 12: 769-779. Bongard-Pierce, D. K., Evans, M. M. S., and Poethig, R. S. (1996) Heteroblastic features of leaf anatomy in maize and their genetic regulation. Int. J. Plant Sci. 157: 331-340. Evans, M. M. S. and Poethig, R. S. (1995) Gibberellins promote vegetative phase change and reproductive maturity in maize. Plant Physiol. 108: 475-487. Evans, M. M. S., Passas, H. J., and Poethig, R. S. (1994) Heterochronic effects of glossy15 mutations on epidermal cell identity in maize. Development 120: 1971-1981.