Genetics of Symbiosis inLotus japonicus: Recombinant Inbred Lines, Comparative Genetic Maps, and Map Position of 35 Symbiotic Loci

Abstract

Sandal et al. MPMI 4 INTRODUCTIONGenetic analysis and application of genetic approaches in the model legume Lotus japonicus (Handberg and Stougaard 1992) has progressed rapidly. Several key genes important for symbiosis with mycorrhizal fungi, root nodule development and other developmental processes have been identified using molecular genetics. The developmental regulators Nin (Schauser et al. 1999) and Pfo (Zhang et al. 2002) were isolated by transposon tagging while map-based cloning led to the molecular characterisation of Har1, SymRK, Nfr1, Nfr5, Castor and Pollux involved in autoregulation, Nod-factor signal perception or signal transduction (Schauser et al. 1999, Krusell et al. 2002 Nishimura et al. 2002a;Stracke et al. 2002;Radutoiu et al. 2003;Madsen et al. 2003; Imaizumi-Anraku et al. 2005). Genetic loci required for the early stages of endosymbiosis have attracted particular interest. Diallelic crosses together with phenotypical studies defined seven loci, SymRK, Nup133, Castor, Pollux, Sym6, Sym15,Sym24, in the common pathway required for both rhizobial and mycorrhizal symbiosis (Kistner et al. unpublished data) and map-based cloning of these loci has been accomplished or is advancing rapidly. A similar interest and effort is now emerging for genetic dissection of nodule organogenesis and function using the Fix -mutants arrested at various stages of nodule development or impaired in nodule function. Cloning of the Sst1 sulfate transporter required in functional root nodules is a first example (Krusell et al. 2005).Continuous isolation of new plant mutant lines is important for completing the genetic dissection of symbiosis and so far six independent mutant populations have been obtained by chemical (EMS) mutagenesis (Perry et al. 2003;Szczyglowski et al. 1998; Webb et al. unpublished data; Gresshoff et al. unpublished data), four populations after T-DNA or transposon insertion mutagenesis (Thykjaer et al. 1995;Schauser et al. 1998;Webb et al. 2000; Gresshoff et al. unpublished data), one population made with fast neutrons (Gresshoff et al. unpublished Umehara and Kouchi (unpublished data). All in all more than 400 symbiotic Lotus mutant lines were identified by screening in these populations and more are likely to follow. Assignment to complementation groups is next logical step in order to determine the number of loci involved, identify all alleles that contribute to phenotypic characterisation of mutants and genotyping of loci. However, diallelic crossing is a relatively slow process where progress is determined by generation time and slowed by a continuously increasing number of individual crosses necessary to keep up with mutant isolation programs. Given the number of symbiotic mutant lines already available and considering the time used to define seven complementation groups with a total of 26 alleles constituting the common pathway (Kistner et al. unpublished data), this approach is unlikely to encompass all alleles in near future. Detection of alleles in already cloned genes ...

NUCLEOPORIN85 Is Required for Calcium Spiking, Fungal and Bacterial Symbioses, and Seed Production in Lotus japonicus

“…The Ljsym24 and Ljsym85 loci were previously shown to be required for both rhizobial and AM symbioses (Szczyglowski et al, 1998;Kawaguchi et al, 2005;Kistner et al, 2005;Sandal et al, 2006). The Ljsym73 loci were reported as low nodulation mutants (Kawaguchi et al, 2002).…”

“…nup85-1 (Ljsym24), nup85-2 (Ljsym73), and nup85-3 (Ljsym85) are alleles affecting AM and nodule symbioses in mutants isolated from ethyl methanesulfonatemutagenized L. japonicus B-129 (Szczyglowski et al, 1998;Kawaguchi et al, 2002Kawaguchi et al, , 2005Sandal et al, 2006). For allelism test, plants were crossed reciprocally according to Jiang and Gresshoff (1997).…”

“…This initial observation has now been extended to several legume species (Gianinazzi-Pearson, 1996), thus defining the so-called common symbiosis (Sym) pathway (Kistner and Parniske, 2002). Three genes, Does Not Make Infections1 (DMI1), DMI2, and DMI3, from Medicago truncatula (Endre et al, 2002;Ané et al, 2004;Lé vy et al, 2004;Mitra et al, 2004) and at least seven loci, SymRK, CASTOR,POLLUX,NUP133,CCaMK,Lj Sym6/30/82,and Lj Sym24/73/85, from L. japonicus have been defined thus far as elements of the common Sym pathway (Kistner et al, 2005;Sandal et al, 2006).…”

Rearrangement of Actin Cytoskeleton Mediates Invasion ofLotus japonicusRoots byMesorhizobium loti

“…The Nap1 locus was mapped to the L. japonicus linkage group 4 flanked by the TM0227 and TM0347 markers (Sandal et al, 2006). Fine mapping and subsequent genotyping of 1077 nap1-1 mutant plants identified markers TM1846 and TM0229, which delimited the Nap1 locus to a 0.4-centimorgan (cM) region, as defined by 12 and 6 recombinations on each side, respectively (see Supplemental Figure 1 online).…”

Identification of QTLs for shoot and root growth under ionic–osmotic stress in Lotus, using a RIL population

“…The species Lotus japonicus has been selected and investigated as model plant for genetic and genomic studies (Handberg and Stougaard 1992;Hayashi et al 2001;Pedrosa et al 2002;Young et al 2005;Sandal et al 2006;Sato et al 2008;Sandal et al 2012). Lotus japonicus is a perennial species closely related to birdsfoot trefoil (L. corniculatus), an important forage legume.…”