|
|
||||||||
|
Plant Physiology 149:137-141 (2009) © 2009 American Society of Plant Biologists Foxtail Millet: A Sequence-Driven Grass Model System[W]Department of Botany, Oklahoma State University, Stillwater, Oklahoma 74078 (A.N.D.); Department of Biology, University of Missouri, St. Louis, Missouri 63121 (E.A.K.); and Department of Crop and Soil Sciences and Department of Plant Biology (K.M.D.), and Department of Genetics (J.L.B.), University of Georgia, Athens, Georgia 30602
Foxtail millet (Setaria italica) is a small diploid C4 panicoid crop species, whose genome is being sequenced by the Joint Genome Institute (JGI) of the Department of Energy. The rationale for sequencing foxtail millet is that it is closely related to the bioenergy grasses switchgrass (Panicum virgatum), napiergrass (Pennisetum purpureum), and pearl millet (Pennisetum glaucum), yet is a more tractable experimental model because of its small diploid genome (1C genome size = 490 Mb) and inbreeding nature. This compares to the larger genomes of the outbreeding species pearl millet (diploid, 1C = 2,352 Mb), napiergrass (tetraploid, 1C = 2,254 Mb), and switchgrass (tetraploid, 1C =1,372–1,666 Mb, octaploid 1C = 2,352–3,136 Mb; Bennett et al., 2000
Foxtail millet will be useful as an experimental crop to investigate many aspects of plant architecture, genome evolution, and physiology in the bioenergy grasses. Foxtail millet, pearl millet, napiergrass, maize (Zea mays), and sorghum (Sorghum bicolor) differ from switchgrass in the decarboxylation enzyme used during C4 photosynthesis (NADP-malic versus NAD-malic; Watson and Dallwitz, 1992
The earliest archeological remains of foxtail millet are found in northern China, in the Cishan and Peiligang ruins in the Yellow River Valley, approximately 7,400 years before present (BP) and 7,935 years BP, respectively (Li and Wu, 1996
Phylogenetic analyses using both chloroplast and nuclear genes show foxtail and green millet (Setaria viridis) as close relatives (Giussani et al., 2001
Isozyme and DNA analyses of green and foxtail millet have shown a high level of diversity (Wang et al., 1995
Foxtail millet and switchgrass last shared a common ancestor about 13 ± 3 million years ago (Vicentini et al., 2008
Foxtail millet has a relatively small stature, with plants of different accessions varying from 20 to 215 cm tall (Reddy et al., 2006
Foxtail millet has a typical domesticated plant architectural form consisting of a single stalk or a few tillers, with large inflorescences that mature more or less at the same time (Fig. 1). Its wild progenitor, green millet, has tillers and axillary branches that appear over the life of the plant, and inflorescences that readily shatter to release the seed at maturity (Defelice, 2002
Foxtail millet varieties can also be remarkably drought and salt tolerant, and further breeding for these characteristics can increase the usefulness of foxtail millet for semiarid and marginal lands (Li and Wu, 1996
Collection of foxtail millet landraces in China started in the 1920s and more than 26,000 accessions, 90% of which are landraces, are currently preserved at the Chinese National Genebank in Beijing. Smaller germplasm collections are maintained at the International Crops Research Institute for the Semi-Arid Tropics, Patancheru, India (1,534 accessions from 26 countries), the National Institute of Agrobiological Sciences, Tsukuba, Japan (1,279 accessions), and the Plant Genetic Resources Conservation Unit of the U.S. Department of Agriculture-Agricultural Research Service (766 accessions; Supplemental Table S1). Phenotypic characterization of the collected materials has indicated that foxtail millet germplasm is highly diverse (Li and Wu, 1996
Two complete genetic maps were created in the late 1990s using RFLP markers (Devos et al., 1998
Yugu1, a highly inbred commercial line from China, was selected for genomic sequencing. This was instead of the accession of foxtail millet used to generate the interspecies genetic map, because that accession showed partial male cytoplasmic infertility (Wang et al., 1998 The genome of green millet inbred A10 will be sequenced using next generation sequencing technology and compared with the Yugu1 sequence to identify a set of >1,500 single nucleotide polymorphism markers for the construction of a high-density genetic map in a newly generated cross between Yugu1 and green millet accession A10. The single nucleotide polymorphism-based genetic map will be used to anchor the genomic sequence, facilitate comparative genomic analysis, and allow quantitative trait loci (QTL) analyses of biomass traits. An approximately 8.1x fosmid library from green millet inbred A10 has recently been constructed, and five randomly selected clones from this library have been sequenced (A.C. Pontaroli and J.L. Bennetzen, unpublished data). One of the clones contained tandem ribosomal DNA repeats, while the other four clones contained numerous nuclear genes that exhibited excellent colinearity with the rice genome (A.C. Pontaroli and J.L. Bennetzen, unpublished data).
Foxtail millet has been adopted as a high-throughput platform for virus-induced gene silencing to model gene inhibition results that have been technically more difficult in switchgrass (R. Nelson, personal communication). Progress is also being made in developing an efficient transformation system for foxtail millet, necessary for testing mechanistic hypotheses of gene action. Embryogenic callus cultures (Rao et al., 1988
For the familiar model systems such as Arabidopsis (Arabidopsis thaliana), rice, or maize, a fully sequenced genome was the culmination of decades of genetic study, and was the tool that laced together many disparate strands of research. In contrast, for foxtail millet, as for Brachypodium and other novel model systems, the fully sequenced genome is the foundation on which genetic resources will be built. Foxtail millet and Brachypodium illustrate a novel way to create a model, in which the basic genome structure is given and can be interpreted by comparison to the other grasses. QTL studies, forward genetics, and reverse genetics can then proceed rapidly, and in a comparative context from the outset. Foxtail millet provides a valuable tool for investigating the C4 grasses, particularly those that are being developed as biomass sources for biofuel production. It was chosen as a target model system as much for its phylogenetic position and its photosynthetic pathway as for its ease of growth and small genome size. Such choices will become increasingly common in the future, as sequencing costs continue to drop. Model systems can be chosen for their ability to address particular questions or to represent particular phylogenetic groups. This approach is especially promising in grasses, where the presence of several completed genomes (and the promise of more) provides an evolutionary genomic context for each new species sequenced. Multiple sequenced genomes, coupled with the ease of comparative analysis among the highly colinear chromosomes of grasses, allow new genomic sequences to be successfully annotated and related to genetic information from other grass species.
The foxtail millet genome will be useful not only for understanding the genetics of biomass production with application to biofuel grasses, but also for the favorable agronomic characteristics of foxtail millet itself. Although foxtail millet is a minor North American grain, it is grown extensively in northern China, Mongolia, India, and Russia, and is also grown for hay in the northern and western Great Plains in the United States (Baltensperger, 1996 However, even with the planned genomic sequence analyses, EST discovery process, genetic map improvements, and QTL analyses, foxtail millet lacks some essential tools needed to become an ideal model system. Mutagenized populations are few, as are reverse genetics tools for characterization of gene function. An expression array has been constructed to examine gene expression under drought stress, but, to our knowledge, neither additional expression arrays nor metabolomic and proteomic tools are yet under development. These will be needed to provide comprehensive analyses of gene function. However, the presence of a completed genome sequence and the current perception of an urgent need to develop herbaceous sources of biomass for biofuel production will provide a powerful impetus to create a full genetic and genomic toolkit in foxtail millet. In response to this challenge, researchers from the United States, China, France, and Japan are beginning to collaborate to fast track tool development in this promising model species.
The following materials are available in the online version of this article.
Received September 8, 2008; accepted November 6, 2008; published January 7, 2009.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Andrew N. Doust (andrew.doust{at}okstate.edu).
[W] The online version of this article contains Web-only data. www.plantphysiol.org/cgi/doi/10.1104/pp.108.129627 * Corresponding author; e-mail andrew.doust{at}okstate.edu.
Austin DF (2006) Fox-tail millets (Setaria:Poaceae)—abandoned food in two hemispheres. Econ Bot 60: 143–158[CrossRef][Web of Science] Baltensperger DD (1996) Foxtail and proso millet. In J Janick, ed, Progress in New Crops. ASHS Press, Alexandria, VA, pp 182–190 Baltensperger DD (2002) Progress with proso, pearl, and other millets. In J Janick, A Whipley, eds, Trends in New Crops and New Uses. ASHS Press, Alexandria, VA, pp 100–103 Benabdelmouna A, Abirached-Darmency M, Darmency H (2001) Phylogenetic and genomic relationships in Setaria italica and its close relatives based on the molecular diversity and chromosomal organization of 5S and 18S-5.8S-25S rDNA genes. Theor Appl Genet 103: 668–677[CrossRef][Web of Science] Bennett MD, Bhandol P, Leitch IJ (2000) Nuclear DNA amounts in angiosperms and their modern uses—807 new estimates. Ann Bot (Lond) 86: 859–909 Darmency H, Zangre GR, Pernes J (1987) The wild-weed-crop complex in Setaria—a hybridization study. Genetica 75: 103–107[CrossRef][Web of Science] de Wet JMJ, Harlan JR (1975) Weeds and domesticates: evolution in the man-made habitat. Econ Bot 29: 99–107[Web of Science] Defelice MS (2002) Green foxtail, Setaria viridis (L.) P. Beauv. Weed Technol 16: 253–257[CrossRef] Dekker J (2003) The foxtail (Setaria) species-group. Weed Sci 51: 641–656[CrossRef] Devos KM, Wang ZM, Beales J, Sasaki T, Gale MD (1998) Comparative genetic maps of foxtail millet (Setaria italica) and rice (Oryza sativa). Theor Appl Genet 96: 63–68[CrossRef][Web of Science] Diao X (2005) Advances in foxtail millet biotechnology and its future directions. Journal of Hebei Agricultural Sciences 9: 61–68 Diao X (2007) Foxtail millet production in China and its future development tendency. In Y Chai, FS Wan, eds, The Industrial Development of China Special Crops. Chinese Agricultural Science and Technology Press, Beijing, pp 32–43 Doust AN, Devos KM, Gadberry MD, Gale MD, Kellogg EA (2004) Genetic control of branching in foxtail millet. Proc Natl Acad Sci USA 101: 9045–9050 Doust AN, Kellogg EA (2006) Effect of genotype and environment on branching in weedy green millet (Setaria viridis) and domesticated foxtail millet (Setaria italica) (Poaceae). Mol Ecol 15: 1335–1349[CrossRef][Medline] Doust AN, Penly AM, Jacobs SWL, Kellogg EA (2007) Congruence, conflict, and polyploidization shown by nuclear and chloroplast markers in the monophyletic "Bristle clade" (Paniceae, Panicoideae, Poaceae). Syst Bot 32: 531–544[CrossRef] Fukunaga K, Domon E, Kawase M (1997) Ribosomal DNA variation in foxtail millet, Setaria italica (L.) P. Beauv., and a survey of variation from Europe and Asia. Theor Appl Genet 95: 751–756[CrossRef][Web of Science] Fukunaga K, Ichitani K, Kawase M (2006) Phylogenetic analysis of the rDNA intergenic spacer subrepeats and its implication for the domestication history of foxtail millet, Setaria italica. Theor Appl Genet 113: 261–269[CrossRef][Web of Science][Medline] Fukunaga K, Ichitani K, Taura S, Sato M, Kawase M (2005) Ribosomal DNA intergenic spacer sequence in foxtail millet, Setaria italica (L.) P. Beauv. and its characterization and application to typing of foxtail millet landraces. Hereditas 142: 38–44[CrossRef][Web of Science][Medline] Fukunaga K, Wang ZM, Kato K, Kawase M (2002) Geographical variation of nuclear genome RFLPs and genetic differentiation in foxtail millet, Setaria italica (L.) P. Beauv. Genet Resour Crop Evol 49: 95–101[CrossRef] Garvin DF (2007) Brachypodium: a new monocot model plant system emerges. J Sci Food Agric 87: 1177–1179[CrossRef][Web of Science] Garvin DF, Gu YQ, Hasterok R, Hazen SP, Jenkins G, Mockler TC, Mur LAJ, Vogel JP (2008) Development of genetic and genomic research resources for Brachypodium distachyon, a new model system for grass crop research. Crop Sci 48: S69–S84[CrossRef][Web of Science] Giussani LM, Cota-Sanchez JH, Zuloaga FO, Kellogg EA (2001) A molecular phylogeny of the grass subfamily Panicoideae (Poaceae) shows multiple origins of C4 photosynthesis. Am J Bot 88: 1993–2012 Jarvis DI, Hodgkin T (1999) Wild relatives and crop cultivars: detecting natural introgression and farmer selection of new genetic combinations in agroecosystems. Mol Ecol 8: S159–S173[CrossRef] Jusuf M, Pernes J (1985) Genetic-variability of foxtail millet (Setaria-Italica P Beauv)—electrophoretic study of 5 isoenzyme systems. Theor Appl Genet 71: 385–391[Web of Science] Kawase M, Fukunaga K, Kato K (2005) Diverse origins of waxy foxtail millet crops in East and Southeast Asia mediated by multiple transposable element insertions. Mol Genet Genomics 274: 131–140[CrossRef][Web of Science][Medline] Kawase M, Sakamoto S (1984) Variation, geographical-distribution and genetic-analysis of esterase isozymes in foxtail millet, Setaria-Italica (L) P-Beauv. Theor Appl Genet 67: 529–533[CrossRef][Web of Science] Kawase M, Sakamoto S (1987) Geographical-distribution of landrace groups classified by hybrid pollen sterility in foxtail millet, Setaria-Italica (L) Beauv,P. Jpn J Breed 37: 1–9 Le Thierry d'Ennequin M, Panaud O, Toupance B, Sarr A (2000) Assessment of genetic relationships between Setaria italica and its wild relative S. viridis using AFLP markers. Theor Appl Genet 100: 1061–1066[CrossRef][Web of Science] Le Thierry d'Ennequin M, Toupance B, Robert T, Godelle B, Gouyon PH (1999) Plant domestication: a model for studying the selection of linkage. J Evol Biol 12: 1138–1147[CrossRef][Web of Science] Lee GA, Crawford GW, Liu L, Chen XC (2007) Plants and people from the early neolithic to Shang periods in North China. Proc Natl Acad Sci USA 104: 1087–1092 Li HW, Li CH, Pao WK (1944) Cytological and genetical studies of the interspecific cross of the cultivated foxtail millet, Setaria italica (L.) Beauv., and the green foxtail millet, S. viridis L. J Am Soc Agron 9: 32–54 Li HW, Li CH, Pao WK (1945) Cytological and genetical studies of the interspecific cross of the cultivated foxtail millet, Setaria-Italica (L) Beauv, and the green foxtail millet, S-Viridis L. J Am Soc Agron 37: 32–54 Li Y, Jia JZ, Wang Y, Wu SZ (1998) Intraspecific and interspecific variation in Setaria revealed by RAPD analysis. Genet Resour Crop Evol 45: 279–285[CrossRef] Li Y, Wu SZ (1996) Traditional maintenance and multiplication of foxtail millet (Setaria italica (L) P. Beauv.) landraces in China. Euphytica 87: 33–38[CrossRef][Web of Science] Liu Y, Yu J, Zhao Q, Zhu D, Ao G (2005) Genetic transformation of millet (Setaria italica) by Agrobacterium-mediated. Chin J Agr Biotechnol 13: 32–37 Liu YH, Yu JJ, Ao GM, Zhao Q (2007) Factors influencing Agrobacterium-mediated transformation of foxtail millet (Setaria italica). Chin J Biochem Mol Biol 23: 531–536 Nakayama H, Afzal M, Okuno K (1998) Intraspecific differentiation and geographical distribution of Wx alleles for low amylose content in endosperm of foxtail millet, Setaria italica (L.) Beauv. Euphytica 102: 289–293[CrossRef][Web of Science] Rao AM, Kishor PBK, Reddy LA, Vaidyanath K (1988) Callus induction and high-frequency plant-regeneration in Italian millet (Setaria-Italica). Plant Cell Rep 7: 557–559[CrossRef][Web of Science] Reddy V, Upadhyaya, Gowda C (2006) Characterization of world's foxtail millet germplasm collections for morphological traits. Journal of SAT Agricultural Research 2: 1–3 Swigonova Z, Lai JS, Ma JX, Ramakrishna W, Llaca V, Bennetzen JL, Messing J (2004) Close split of sorghum and maize genome progenitors. Genome Res 14: 1916–1923 Vicentini A, Barber JC, Aliscioni AA, Giussani LM, Kellogg EA (2008) The age of the grasses and clusters of origins of C4 photosynthesis. Glob Change Biol 14: 2693–2977 Vishnoi RK, Kothari SL (1996) Somatic embryogenesis and efficient plant regeneration in immature inflorescence culture of Setaria italica (L) Beauv. Cereal Res Commun 24: 291–297 Wang R-L, Wendel JF, Dekker JH (1995) Weedy adaptation in Setaria spp. I. Isozyme analysis of genetic diversity and population genetic structure in Setaria viridis. Am J Bot 82: 308–317[CrossRef][Web of Science] Wang ZM, Devos KM, Liu CJ, Wang RQ, Gale MD (1998) Construction of RFLP-based maps of foxtail millet, Setaria italica (L.) P. Beauv. Theor Appl Genet 96: 31–36[CrossRef][Web of Science] Watson L, Dallwitz M (1992) The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. http://delta-intkey.com (June 6, 2008) Zhang JP, Liu TS, Fu JJ, Zhu Y, Jia JP, Zheng J, Zhao YH, Zhang Y, Wang GY (2007) Construction and application of EST library from Setaria italica in response to dehydration stress. Genomics 90: 121–131[CrossRef][Web of Science][Medline] Zuloaga FO, Morrone O, Giussani LM (2000) A cladistic analysis of the Paniceae: a preliminary approach. In SWL Jacobs, J Everett, eds, Grasses: Systematics and Evolution. CSIRO, Collingwood, Victoria, Australia, pp 123–135 Related articles in Plant Physiol.:
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ASPB Publications | PLANT PHYSIOLOGY® | THE PLANT CELL | |
|---|---|---|---|