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First published online May 20, 2005; 10.1104/pp.105.061408 Plant Physiology 138:990-997 (2005) © 2005 American Society of Plant Biologists Rapid Array Mapping of Circadian Clock and Developmental Mutations in Arabidopsis1Department of Cell Biology and Institute for Childhood and Neglected Diseases, Scripps Research Institute, La Jolla, California 92037 (S.P.H., F.G.H., J.L.P.-P., T.F.S., M.J.Y., S.A.K.); and Plant Biology and Genomic Analysis Laboratory, Salk Institute, La Jolla, California 92037 (J.O.B., S.J.L., J.R.E.)
Classical forward genetics, the identification of genes responsible for mutant phenotypes, remains an important part of functional characterization of the genome. With the advent of extensive genome sequence, phenotyping and genotyping remain the critical limiting variables in the process of map-based cloning. Here, we reduce the genotyping problem by hybridizing labeled genomic DNA to the Affymetrix Arabidopsis (Arabidopsis thaliana) ATH1 GeneChip. Genotyping was carried out on the scale of detecting greater than 8,000 single feature polymorphisms from over 200,000 loci in a single assay. By combining this technique with bulk segregant analysis, several high heritability development and circadian clock traits were mapped. The mapping accuracy using bulk pools of 26 to 100 F2 individuals ranged from 0.22 to 1.96 Mb of the mutations revealing mutant alleles of EARLY FLOWERING 3, EARLY FLOWERING 4, TIMING OF CAB EXPRESSION 1, and ASYMMETRIC LEAVES 1. While direct detection of small mutations, such as an ethyl-methane sulfonate derived single base substitutions, is limited by array coverage and sensitivity, large deletions such as those that can be caused by fast neutrons are easily detected. We demonstrate this by resolving two deletions, the 77-kb flavin-binding, kelch repeat, f-box 1 and the 7-kb cryptochrome2-1 deletions, via direct hybridization of mutant DNA to ATH1 expression arrays.
The properties that originally made organisms such as yeast (Saccharomyces cerevisiae), nematode (Caenorhabditis elegans), Arabidopsis (Arabidopsis thaliana), and fruit fly (Drosophila melanogaster) models for scientific research were their amenability to genetic studies: easily reared short life cycle, simple controlled mating, and fecundity. Only later was the serendipity of their small genomes realized and capitalized on by sequencing their entire genomes. A fully sequenced and annotated genome alone has limited value in revealing the functional relevance of genes. Forward genetics via mutagenesis is a traditional approach to assign gene function. This practice involves the identification of phenotypically divergent individuals and subsequent identification of the causal genetic difference, thereby connecting a gene with a phenotype and/or function. Advances in genome biology have facilitated this approach, thus increasing the usefulness of model systems for determining the role of genes in organismal physiology.
In Arabidopsis, genetic variation is commonly induced with the chemical mutagen ethyl-methane sulfonate (EMS), which alkalates guanine residues (Koornneef, 2002
Besides genetic variation created by mutagens, there is extensive naturally occurring variation among Arabidopsis accessions. That variation can be exploited within a segregating population to mark loci associated with a phenotype. Sequencing projects have identified several thousand polymorphisms that serve as anchored molecular markers (Schmid et al., 2003
High-density oligonucleotide arrays are an effective platform to measure numerous polymorphic loci in a single assay (Hazen and Kay, 2003
A very practical, effective, and rapid approach to using SFPs for mapping mutations is in combination with bulk segregant analysis (BSA; Michelmore et al., 1991 Here, we report the results of several empirical studies mapping EMS mutations in genes involved in development (asymmetric leaves 1 [as1]), and the circadian clock (early flowering 3 [elf3], early flowering 4 [elf4], and timing of cab expression 1 [toc1]). In each case, BSA mapping with SFP genotyping rapidly mapped the mutation to a rough interval suitable for fine mapping or direct sequencing of candidate genes. We also demonstrate an approach to identify mutant loci without having to make a mapping cross, by directly delineating the fast neutron derived deletions responsible for flowering time mutations flavin-binding, kelch repeat, f-box 1 (fkf1) and cryptochrome2-1 (cry2-1).
Isolating and Mapping Circadian Clock Mutants
The circadian clock allows an organism to anticipate environmental changes and time specific physiological events to occur at certain times of day. A powerful laboratory tool used as an indicator of the clock is LUCIFERASE (LUC) fused with the promoter of a circadian regulated gene, namely, CHLOROPHYLL A-B BINDING PROTEIN 2 (CAB2; Millar et al., 1995
The F2 populations segregating for arrhythmic phenotype (Fig. 1A) derived from a cross with Ler were classified into discrete categories, either rhythmic or not in segregants that contained the CAB2::LUC reporter. Segregation was consistent with a single recessive mutation for each of the three populations (data not shown). As the mutations are in the Col background, at the mutant locus and linked regions, the arrhythmic group was homozygous Col and the rhythmic (wild-type) group a 2:1 mixture of heterozygotes and homozygous Ler. Unlinked loci are of roughly equal proportion of Col and Ler alleles in both bulk pools. Thus, the largest difference in allele frequency between the pools is the predicted location of the mutation. The greatest difference in allele frequency between the arr23xLer arrhythmic F2s and the rhythmic F2s was near the bottom of chromosome 2 at 11.288 Mb, very near the circadian clock component, ELF3 (Fig. 2). The mutant phenotype of elf3 is similar to arr23 making ELF3 a candidate gene (Hicks et al., 1996
Following the same procedure, the arr44 mutation was quickly mapped to the bottom of chromosome 2 at 18.701 Mb, well below ELF3 (Fig. 2). Besides elf3, the only other gene in the region known to cause CAB2::LUC arrhythmia and long hypocotyl when mutated is ELF4 (Doyle et al., 2002
As opposed to the discrete classification of rhythmic versus arrhythmic phenotype, circadian period is a quantitative measurement. Such period mutants could be mapped as quantitative trait loci using extreme array mapping, by selecting pools of extreme phenotype plants from an F2 distribution (Borevitz et al., 2003
In addition to analyzing mutants defective in controlling their circadian clocks, we successfully used array-based bulk segregant mapping to position mutations that affect leaf and flower development. To isolate floral organ shedding mutants in Arabidopsis, mature M2 plants from an EMS-mutagenized Ler population were screened for defects in this process. An isolated mutant with defects in both flower and leaf development was named bibb (bib) due to the resemblance of its rumpled leaves with short petioles to Bibb lettuce (Fig. 3D). Three additional mutants with a bib-like appearance were isolated from this and a previous screen (Liljegren et al., 2000
An F2 mapping population derived from a cross of bib-1 to Col segregated in the expected ratio for a single recessive mutation; mutants were readily distinguished from wild type at the rosette stage. Bulk segregant array genotyping positioned the bib mutation on chromosome 2 (Fig. 2) within 1.68 Mb of ASYMMETRIC LEAVES1 (AS1). AS1 encodes a Myb-domain transcription factor that negatively regulates expression of KNOX homeobox genes in developing lateral organ primordia (Byrne et al., 2000
Using replicate samples and initially only a partial genome array, 105 potential natural deletions were detected between Col and Ler (Borevitz et al., 2003
The fkf1 fast neutron induced deletion was estimated to be 65 to 80 kb (Nelson et al., 2000
The fast neutron mutant cry2-1 is photoperiod insensitive and late flowering (Guo et al., 1998
High-Density Genome Coverage Map-based cloning first relies on detecting an association between a marker genotype and a phenotype. Subsequently, mapping resolution is a function of marker density and number of recombination events. With the 8,000 confident SFPs used here, marker resolution was on average every 15 kb. With new whole genome tiling arrays, we expect an SFP on average every 700 bp; thus, marker density is no longer limiting. By using pools of recombinant lines, we increase the number of recombination events assayed in a single hybridization; however, the rare close recombination events are diluted. An important advance toward the fine mapping of novel loci will take advantage of pools of preselected recombinant lines for array genotyping when clear candidates are not identified. Here, a fine recombination event can be fully exploited with high-density SFPs.
If our candidate genes are all correct, the array mapping accuracy of the examples described ranged from 0.222 to 2.396 Mb. This corresponds well with the 7 cM 95% credible interval determined by simulations (Borevitz, 2005
SFP discovery was conducted via the comparison of replicate arrays of Col and Ler. Beyond the sequence necessary to design the oligonucleotide array, sequencing other accessions is not necessary for array-based genotyping and mapping. Any two accessions can be used in a cross to BSA map with SFPs following replicate hybridizations of both accessions and the identification of polymorphic features.
We have shown that induced deletions the size of a gene size or greater can be readily identified by direct hybridization of DNA from mutant lines in comparison with wild-type controls. Future generations of whole genome tiling arrays (Borevitz and Ecker, 2004
Isolation and Analysis Mutants
The isolation and analysis of circadian mutants has been previously described (S.P. Hazen, T.F. Schultz, J.L. Pruneda-Paz, J.O. Borevitz, J.R. Ecker, and S.A. Kay, unpublished data). The isolation of developmental mutants has also been described (Liljegren et al., 2000
This method has been described in detail (Borevitz, 2005
Deletion mapping for fast neutron mutations was performed similarly to the prediction of potential natural deletions (Borevitz, 2005
We thank H. Bird Richardson for expert assistance with figure formatting. Received February 16, 2005; returned for revision March 27, 2005; accepted April 13, 2005.
1 This work was supported by the National Institutes of Health (grant nos. GM56006 and GM67837 to S.A.K. and a Ruth L. Kirschstein National Research Service Award postdoctoral fellowship [GM071225] to S.P.H.), by the Department of Energy (grant no. DEFG0300ER15113), by the National Science Foundation (grant no. MCB0213154 to J.R.E.), by the U.S. Department of Agriculture (National Research Initiative Competitive Grants Program postdoctoral fellowship to S.J.L.), and by the Helen Hay Whitney Foundation (fellowship to J.O.B.). F.G.H. is a Department of Energy-Energy Biosciences Fellow of the Life Sciences Research Foundation. This is manuscript number 17134CB of the Scripps Research Institute.
2 These authors contributed equally to the paper.
3 Present address: Ifeva, Facultad de Agronomia, UBA, Av. San Martin 4453, 1417, Buenos Aires, Argentina.
4 Present address: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 97516.
5 Present address: Department of Evolution and Ecology, University of Chicago, Chicago, IL 60608. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.061408. * Corresponding author; e-mail ecker{at}salk.edu; fax 8585586379.
Borevitz JO (2005) Array genotyping genotyping and mapping. In J Salinas, JJ Sanchez-Serrano, eds, Arabidopsis Protocols, Ed 2. Humana Press, Totowa, NJ Borevitz JO, Ecker JR (2004) Plant genomics: the third wave. Annu Rev Genomics Hum Genet 5: 443477[CrossRef][Web of Science][Medline]
Borevitz JO, Liang D, Plouffe D, Chang HS, Zhu T, Weigel D, Berry CC, Winzeler E, Chory J (2003) Large-scale identification of single-feature polymorphisms in complex genomes. Genome Res 13: 513523 Byrne ME, Barley R, Curtis M, Arroyo JM, Dunham M, Hudson A, Martienssen RA (2000) Asymmetric leaves1 mediates leaf patterning and stem cell function in Arabidopsis. Nature 408: 967971[CrossRef][Medline] Dowson-Day MJ, Millar AJ (1999) Circadian dysfunction causes aberrant hypocotyl elongation patterns in Arabidopsis. Plant J 17: 6371[CrossRef][Web of Science][Medline] Doyle MR, Davis SJ, Bastow RM, McWatters HG, Kozma-Bognar L, Nagy F, Millar AJ, Amasino RM (2002) The ELF4 gene controls circadian rhythms and flowering time in Arabidopsis thaliana. Nature 419: 7477[CrossRef][Medline]
Gong JM, Waner DA, Horie T, Li SL, Horie R, Abid KB, Schroeder JI (2004) Microarray-based rapid cloning of an ion accumulation deletion mutant in Arabidopsis thaliana. Proc Natl Acad Sci USA 101: 1540415409
Guo HW, Yang WY, Mockler TC, Lin CT (1998) Regulations of flowering time by Arabidopsis photoreceptors. Science 279: 13601363 Hazen SP, Kay SA (2003) Gene arrays are not just for measuring gene expression. Trends Plant Sci 8: 413416[CrossRef][Web of Science][Medline]
Hicks KA, Albertson TM, Wagner DR (2001) EARLY FLOWERING3 encodes a novel protein that regulates circadian clock function and flowering in Arabidopsis. Plant Cell 13: 12811292
Hicks KA, Millar AJ, Carre IA, Somers DE, Straume M, Meeks-Wagner DR, Kay SA (1996) Conditional circadian dysfunction of the Arabidopsis early-flowering 3 mutant. Science 274: 790792
Jander G, Norris SR, Rounsley SD, Bush DF, Levin IM, Last RL (2002) Arabidopsis map-based cloning in the post-genome era. Plant Physiol 129: 440450 Koornneef M (2002) Classical mutagenesis in higher plants. In PM Gilmartin, C Bowler, eds, Molecular Plant Biology, Ed Vol 1. Oxford University Press, pp 111 Liljegren SJ, Ditta GS, Eshed HY, Savidge B, Bowman JL, Yanofsky MF (2000) SHATTERPROOF MADS-box genes control seed dispersal in Arabidopsis. Nature 404: 766770[CrossRef][Medline]
Michelmore RW, Paran I, Kesseli RV (1991) Identification of markers linked to disease-resistance genes by bulked segregant analysis: a rapid method to detect markers in specific genomic regions by using segregating populations. Proc Natl Acad Sci USA 88: 98289832
Millar AJ, Carre IA, Strayer CA, Chua NH, Kay SA (1995) Circadian clock mutants in Arabidopsis identified by luciferase imaging. Science 267: 11611163 Mockler TC, Chan S, Sundareson A, Chen H, Jacobsen SE, Ecker JR (2005) Applications of DNA tiling arrays for whole-genome analysis. Genomics 85: 115[CrossRef][Web of Science][Medline] Nelson DC, Lasswell J, Rogg LE, Cohen MA, Bartel B (2000) FKF1, a clock-controlled gene that regulates the transition to flowering in Arabidopsis. Cell 101: 331340[CrossRef][Web of Science][Medline] Ori N, Eshed Y, Chuck G, Bowman JL, Hake S (2000) Mechanisms that control knox gene expression in the Arabidopsis shoot. Development 127: 55235532[Abstract]
Schmid KJ, Sorensen TR, Stracke R, Torjek O, Altmann T, Mitchell-Olds T, Weisshaar B (2003) Large-scale identification and analysis of genome-wide single-nucleotide polymorphisms for mapping in Arabidopsis thaliana. Genome Res 13: 12501257 Semiarti E, Ueno Y, Tsukaya H, Iwakawa H, Machida C, Machida Y (2001) The asymmetric leaves2 gene of Arabidopsis thaliana regulates formation of a symmetric lamina, establishment of venation and repression of meristem-related homeobox genes in leaves. Development 128: 17711783[Abstract] The Arabidopsis Genome Initiative (2000) Analysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature 408: 796815[CrossRef][Medline] Torii KU, Mitsukawa N, Oosumi T, Matsuura Y, Yokoyama R, Whittier RF, Komeda Y (1996) The Arabidopsis ERECTA gene encodes a putative receptor protein kinase with extracellular leucine-rich repeats. Plant Cell 8: 735746[Abstract] Torjek O, Berger D, Meyer RC, Mussig C, Schmid KJ, Sorensen TR, Weisshaar B, Mitchell-Olds T, Altmann T (2003) Establishment of a high-efficiency SNP-based framework marker set for Arabidopsis. Plant J 36: 122140[CrossRef][Web of Science][Medline] Werner JD, Borevitz JO, Uhlenhaut NH, Ecker JR, Chory J, Weigel D (2005a) FRIGIDA-independent variation in flowering time of natural A. thaliana accessions. Genetics (in press)
Werner JD, Borevitz JO, Warthmann N, Trainer GT, Ecker JR, Chory J, Weigel D (2005b) Natural variation in flowering time of A. thaliana associated with a deletion in the FLC homolog FLM. Proc Natl Acad Sci USA 102: 24602465
Winzeler EA, Castillo-Davis CI, Oshiro G, Liang D, Richards DR, Zhou Y, Hartl DL (2003) Genetic diversity in yeast assessed with whole-genome oligonucleotide arrays. Genetics 163: 7989
Wolyn DJ, Borevitz WO, Loudet O, Schwartz C, Maloof J, Ecker JR, Berry CC, Chory J (2004) Light-response quantitative trait loci identified with composite interval and eXtreme array mapping in Arabidopsis thaliana. Genetics 167: 907917 Zagotta MT, Hicks KA, Jacobs CI, Young JC, Hangarter RP, Meeks-Wagner DR (1996) The Arabidopsis ELF3 gene regulates vegetative photomorphogenesis and the photoperiodic induction of flowering. Plant J 10: 691702[CrossRef][Web of Science][Medline] This article has been cited by other articles:
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