Chapter 5 Genetic Analysis of Apomixis - cimmyt

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progression or inhibition of development.Future screens will also include activationtagging in order to induce genes under aspatial, temporal, or developmental regimethat differs from that in the sexual wild typeplants.Known Gene ApproachesKnown genes used for genetically engineeringthe apomixis trait should lead to the followingbiological processes:(1) avoidance and bypassing of meiosis(apomeiosis);(2) formation, ideally, of one functionalunreduced embryo sac within each ovule;(3) autonomous development of theunreduced egg cell by parthenogenesis;(4) development of a functionalendosperm-this could be autonomousor pseudogamous after fertilization of thecentral cell; and(5) an inducible/repressible system that isnecessary to switch between apomicticand sexual reproduction pathways,because sexuality and recombination willbe required for the introduction of newtraits into crops, which will result in newand improved plant varieties.Based on analyses of mutants in apomictic andsexual plant species, it is unlikely that theapomixis trait can be engineered using a singlegene. Tms is supported by the fact that in mostcases apomixis is facultative and that theproportion of apomictic progeny can beinfluenced by different factors, e.g., byenvironmental factors. Variability witmn thedifferent apomictic reproduction pathwaysfurther indicates that asexual seeddevelopment cannot be explained on the basisof a single gene.One possibility for engineering apomixis isbased on isolating the apomixis gene(s) fromnatural apomicts and inserting them intosexual crops. Molecular mapping of apomixisgenes and gene isolation by map-based cloningor transposon tagging (described byGrimanelliet aI., Chap. 6) are performed in variouslaboratories, but until now no apomixis genescould be isolated and markers still lie withincM distance. One major problem with severalapomicts is suppression of recombinationaround the apomixis loci (e.g., Pennisetum andTripsacum; Grimanelli et aI., Chap. 6). Inaddition, apomictic species do not belong tothe classical model plant species, and thereforepositional cloning is difficult because of therelatively low number of available markers,which are needed to "walk" to the apomixisgene(s). Transposon tagging is not possible formost apomicts (TripsQwm is an exceptionbecause it can easily be crossed with maizelines carrying active transposon elements), andfor the near future, T-DNA tagging will remainrestricted to dicotyledonous apomicts such asHieracium, which are accessible toAgrobacterium tumefaciens transformation(Bicknell, Chap. 8). Moreover, it is also possiblethat because of the polyploid nature of naturalapomicts, no such phenotype exists.Known genes/promoters from sexual speciesthat could be used for genetic engineeringinclude those involved with (i) ovule development,(ii) initiation of meiosis, (iii) femalegametophyte development, (iv) parthenogenesis,and thus autonomous embryodevelopment, and (v) initiation of endospermdevelopment. Grossniklaus (Chap. 12)specul~tes that the genes controlling apomixisare under relaxed or aberrant temporal and/or spatial control, thus developmentalcheckpoints and feedback mechanisms may beignored or altered, leading to precociousdevelopment of the megaspore mother celland/or the unreduced egg cell.Ovule- and nucellus-specific genes/promotersare now available as tools (see Tables 14.1 and14.2). The molecular control of meiosis is wellcharacterized in yeast (Vershon and Pierce2000) and some animal systems, e.g.,
G...tk bgltoeerlog.' Apomixis 10 Seu.1 Cr.ps: ACrilkal A.........I., tile Apomixis Tedo..logy 233Caenorhabditis elegans (Zetka and Rose 1995),and many genes have been isolated andcharacterized during the last few years. Muchless is known about the genes involved in plantmeiosis. However; the first homologs to yeastmeiosis genes were recently isolated (reviewedby Grossniklaus, Chap. 12), and many meiosismutants remain available for furthercharacterization (e.g., in maize and Arabidopsis;Neuffer et al. 1997; Yang and Sundaresan 2000).Genes that are expressed during the inductionof meiosis have been identified in lily(Kobayashi et al. 1994). Most work on meiosisin plants has been accomplished throughinvestigating male meiosis, but for geneticengineering, female meiosis genes will be ofparticular interest. Some genes involved withfemale gametophyte development have beenidentified, of which some are specificallyexpressed in different cells of the femaleTable 14.1 Examples of isolated genes and their promoters that might be useful as tools for de novosynthesis of the apomixis trait in sexual cropsProcess to be monipulatedGene (expression/function)'Apomixis genes'not isolated yet (?)Ovule and nucellus-specific target gene expressionFBPI promoter (ovule-specific)DEFH9 promoter (ovule-specific)WM403 promoter (nucellus-specific)Nucellin eDNA (nucellus-specilic)Prevention of meiosis/ apomeiosisdiverse cDNAs (early meiosis-specific)pAWlL3 eDNA (early meiosis-specific)DMO gene (MMC* -specific)5YNl gene (chrom. condensation/pairing)Parthenogenesis (autonomous embryo development)5ERK gene (competence to form embryos)LfCl gene (competence 10 form embryos)BBM1gene (competence to form embryos)ImE51-4 promoter (embryo sac-specific)(Autonomous) endosperm developmentMWF/51 gene (suppressor)FI52 gene (suppressor)FJEIF/53 gene (suppressor)ImE51-4 promoter (embryo sac-specific)ImprintingMfTl als (hypomethylationJIndudble/ repressoble systemsSteroid-inducible promoterCopper-inducible promoterTetracycline-inducible!-inoctivalable promolerEthanol-inducibele promoter-MMC: Mega- and Microlpore molher cellI.(Origin)(Petunia)(Anthirrhinum)(waler-melon)(barley)(lily)(wheat)(Arabidopsis)(Arabidopsis)(carrot, Arabidopsis)(Arabidopsis)(Brossico, Arobidopsis)(moize)(Arobidopsis)(Arabidopsis)(Arabidopsis)(maize)(Arobidopsis)(mammals)(yeast)(bacterium)(fungus)ReferenceColombo el 01., 1997Rotino el 01., 1997Shen et 01., unpublishedChen and Foolad, 1997Kobayashi et 01., 1994Ji and langridge, 199~Klimyuk and Jones, 1997Bai et 01., 1999Schmidt et 01., 1997lotan el 01., 199BBoutilier et 01., unpublishedAmien and Dresselhaus, unpublishedGrossniklaus et 01., 1998bluo et 01., 1999luo et 01., 1999Ohad et 01., 1999Amien and Dresselhaus, unpublishedAdams el 01., 2000Vinkenoog et 01., 2000Schena et 01., 1991Melt et 01., 1993Weinmann et 01., 1994Caddick el 01., 1998
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(over illustration:Pictured is an i
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Institut de Recherche pour Ie Devel
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iv33 Outlook33 References35 Appendi
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vi131 Screening Procedures: Advanta
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VIIITables4 Table 1.15 Table 1.29 T
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xAcknowledgmentsWe are grateful to
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xiifood crops such as maize, wheat,
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2 Gary H. T....i.....much food as i
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4 Gary H. Toe"'...breeding: the evo
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6 Gary H. T....it....The potential
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Chapter 2Apomixis and the Managemen
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10M.. Be,th.dcategories n + nand 2n
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12 J.&eo BertIoaodtwo tetraploid sp
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14 JoG.. B.rth""dTable 2.8 Distribu
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16 M......thodhexaploidy through 2n
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18 JI&.. lertIoaodheterozygous cond
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20 JM Iertltaodmarkers to retain th
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22 JoA•• BerthudFurthermore, if
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Chapter 3Classification of Apomicti
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26 (llarIesf.(r••3) The Ixeris-
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simultaneous division of the proxim
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30 (\aries f. Crao.differentiating
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32 CWIts F. C,..haploids from norma
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34 cales F. (,...Campbell, C. S., C
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36 GaOO F. er...media. There may al
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38 (IIarIe,F.e-.The following recip
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40 CWIes F.
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42 C"Ie
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Chapter 4Ultrastructural Analysis o
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46 T.""". N. Naomo•• ..dJ...·P
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(Figure 4.2a,b,c). Their cytoplasm
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50 Tomaro N. Naurnovo ond Jeon-Phil
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Figure 4.2 (cont'd)
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54 Tamara N. Nauma.a and J...-Phaip
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56 Tamara H. Haumaya ...d J...-Phmp
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58 Tamara N. N....... Old JOGO-PUIp
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60 T.mar. N. N••may•••dJ
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62 Tamara N. Nouma.o and Jeon-Phmpp
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Chapter 5Genetic Analysis of Apomix
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66 Robe" T. SherwoodIn mitotic dipl
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68 ••It T. Sllorwoodmegasporoge
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70 Robert T. SherwoodIdentification
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72 R....11 T. SlMrwoodwe postulate
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74 Rob.rt T. Sherwoodin the gametop
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76 Rokrt T. SHtwoodPerhaps the most
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78 Robe" T. S~erwoodEnvironment pla
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80 Robert T. SherwoodBanaglio, E. 1
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82 Robe" 1. Sherwood---. 1989. Apom
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84 Dcaitl ~11i-, lot To...., .od Di
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86 Do.lel Griome/I-, Joe To~ ....,
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88 Oaoitl G
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90 o.lel ~II-, Jo. lob.., aod Diego
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and meiotic or developmental mutant
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94 D..iel Grimallelli-, Jo. Tohme,
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96 10k. G.(o,.,..mechanisms (Figure
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98 Jolo.G.(_explain the existence o
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100 JolI.G.C....parameters affectin
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102 1010. G.(arma.was developed in
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104 J... G.(.....effects), which co
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106 J.hG.eforseveral thousand to a
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108 Jelo.G.(_large linkage group in
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11 0 Joh. G.(orma.---. 1997. Asynch
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112 a... A. 8icUeI1993). Before the
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114 ROil A. 8idlooll(Sherwood et al
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116 R... A. IkbeIlinduced mutation
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118 Ron A. Mlltllstudies of apomixi
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120 I... A. BkbollLeblanc, 0., M.D.
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122 Olivier L.bla.,.ncI A.d,ea M.nu
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124 Olivier lt~1ao< aod Aock.. Mau"
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126 OIlrier Ltblaooc ood AocI...Mo,
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128 or..Ie, leblal( allll Aodrea Ma
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130 Ofjyier LH......AodrH Mom","Mar
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132 Olivier leblaoc and Aldr.. Mall
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134 OIivie' I
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136 or..io. u.~100< awd Aod.... M.n
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138 udda lorge. do Val. aod Joh W.
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140 Ca
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142 C«ida Jorge. do Va" aod Jah W.
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144 (..iIda 80rges cit Va" DOd Ja~.
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146 Cacido ....... Vole..J.b W. MIe
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148 Ca
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150 (adlda Borge. da VaNe and Joh.
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152 Ccdda Borge. do v..... J.h W. M
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154 Yve< 5
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156 rn. s.mdaosearch for an opitimu
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158 Yv•• Savid..unreduced polar
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160 Yves SoviclaoBashawet al. (1970
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162 hOI Scrvidao211 = 56 chromosome
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164 r.., SaYid..Transfer of Gene(s)
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166 rves Sqyldaounanswered. However
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Chapter 12From Sexuality to Apomixi
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170 lie. Gros..iklalSgametes and em
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172 Uti Gro....1aosGunning 1990). T
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174 UeIGr.........embryogenesis, wh
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176 U.IGm..lln.apomictic pathway wi
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178 IJeIGr.........development with
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180 Ud Gr....lIoo,(Rhoades and Demp
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Page 220 and 221: 206 UeRG'....ild...--.1974. Reprodu
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Page 226 and 227: Chapter 13Induction of Apomixis inS
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Chapter 5 Genetic Analysis of Apomixis - cimmyt

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