L. Schauser et al., SYMBIOTIC MUTANTS DEFICIENT IN NODULE ESTABLISHMENT IDENTIFIED AFTER T-DNA TRANSFORMATION OF LOTUS-JAPONICUS, MGG. Molecular & general genetics, 259(4), 1998, pp. 414-423
Nitrogen-fixing root nodules develop on legumes as a result of an inte
raction between host plants and soil bacteria collectively referred to
as rhizobia. The organogenic process resulting in nodule development
is triggered by the bacterial microsymbiont, but genetically controlle
d by the host plant genome. Using T-DNA insertion as a tool to identif
y novel plant genes that regulate nodule ontogeny, we have identified
two putatively tagged symbiotic loci, Ljsym8 and Ljsym13, in the diplo
id legume Lotus japonicus. The sym8 mutants are arrested during infect
ion by the bacteria early in the developmental process. The sym13 muta
nts are arrested in the final stages of infection, and ineffective nod
ules are formed. These two plant mutant lines were identified in proge
ny from 1112 primary transformants obtained after Agrobacterium tumefa
ciens T-DNA-mediated transformation of L. japonicus and subsequent scr
eening for defects in the symbiosis with Mesorhizobium loti. Additiona
l nontagged mutants arrested at different developmental stages were al
so identified and genetic complementation tests assigned all the mutat
ions to IG monogenic symbiotic loci segregating recessive mutant allel
es. In the screen reported here independent symbiotic loci thus appear
ed with a frequency of similar to 1.5%, suggesting that a relatively l
arge set of genes is required for the symbiotic interaction.