The Lotus japonicus Genome

7

Genes for Autoregulation of Nodulation

Masayoshi Kawaguchi

Abstract

The phenomenon in which developed nodules or nodule primordia

suppress the emergence of further nodules in legumes is termed

autoregulation of nodulation (AON) (Nutman in Ann Bot 16:79–101,

1952 ). AON consists of two presumptive long-distance signal molecules

involving roots and shoots (Caetano-Anollés and Gresshoff in Annu Rev

Microbiol 45:345–382, 1991 ; Oka-Kira and Kawaguchi in Curr Opin

Plant Biol 9:496–502, 2006 ) (Fig.7.1) and is also related to the repression

of nodules by nitrogen compounds such as nitrate. AON is of great

interest with respect to morphological plasticity of plant organogenesis as

well as long-distance signalling. This chapter is devoted to the current

knowledge of AON mainly inLotus japonicus..

7.1 Hypernodulating Mutants
and HAR1

Mutants defective in AON are expected to lose the
negative feedback control and consequently dis-
play a hypernodulating phenotype with a wider
nodulation zone in their roots. Supernodulating or
hypernodulating mutants such asGlycine max nts/
nark,Lotus japonicus har1,Medicago truncatula
sunnandPisum sativum sym29allow nodules to
develop in almost entire root regions (Carroll et al.
1985 ; Sagan and Duc 1996 ; Schauser et al. 1998 ;
Szczyglowski et al. 1998 ; Wopereis et al. 2000 ;

Kawaguchi et al. 2002 ; Oka-Kira et al. 2005 ;

Schnabel et al. 2005 ). Interestingly, reciprocal

grafting experiments using hypernodulating

mutants and wild-type plants have shown that the

nodulation phenotype in roots is determined by

the shoot genotype (Delves et al. 1986 ). Very

similar results were obtained in other leguminous

species. Thesefindings indicate that the mutated

genes products function in the shoot and that the

feedback regulation of nodulation requires long-

distance signalling between the shoots and the

roots. Positional cloning has revealed thatHAR1

and its orthologs encode an LRR receptor-like

kinase and their functions are conserved among

other legume species (Krusell et al. 2002 ; Ni-

shimura et al. 2002 ; Schnabel et al. 2005 ; Searle

et al. 2003 ). Surprisingly, among all receptor-like

kinases inArabidopsis,theHAR1gene is most

similar toCLAVATA1(CLV1), which is a key

component required for shoot apical meristem

M. Kawaguchi (&)
Division of Symbiotic Systems, National Institute for
Basic Biology, Okazaki, Aichi 444-8585, Japan
e-mail: [email protected]

S. Tabata and J. Stougaard (eds.),The Lotus japonicus Genome, Compendium of Plant Genomes,
DOI 10.1007/978-3-662-44270-8_7,©Springer-Verlag Berlin Heidelberg 2014

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