Isolation and phenotypic characterization of Lotus japonicus mutants specifically defective in arbuscular mycorrhizal formation.
Several symbiotic mutants of legume plants defective in nodulation have also been shown to be mutants related to arbuscular mycorrhizal (AM) symbiosis. The origin of the AM symbiosis can be traced back to the early land plants. It has therefore been postulated that the older system of AM symbiosis was partially incorporated into the newer system of legume-rhizobium symbiosis. To unravel the genetic basis of the establishment of AM symbiosis, we screened about 34,000 plants derived from ethyl methanesulfonate (EMS)-mutagenized Lotus japonicus seeds by microscopic observation. As a result, three lines (ME778, ME966 and ME2329) were isolated as AM-specific mutants that exhibit clear AM-defective phenotypes but form normal effective root nodules with rhizobial infection. In the ME2329 mutant, AM fungi spread their hyphae into the intercellular space of the cortex and formed trunk hyphae in the cortical cells, but the development of fine branches in the arbuscules was arrested. The ME2329 mutant carried a nonsense mutation in the STR-homolog gene, implying that the line may be an str mutant in L. japonicus. On the ME778 and ME966 mutant roots, the entry of AM fungal hyphae was blocked between two adjacent epidermal cells. Occasionally, hyphal colonization accompanied by arbuscules was observed in the two mutants. The genes responsible for the ME778 and ME966 mutants were independently located on chromosome 2. These results suggest that the ME778 and ME966 lines are symbiotic mutants involved in the early stage of AM formation in L. japonicus.
National Agriculture and Food Research Organization (NARO) Institute of Livestock and Grassland Science, Nasushiobara, Tochigi, 329-2793 Japan.
Tomoko
T
Kojima
Katsuharu
K
Saito
Hirosuke
H
Oba
Yuma
Y
Yoshida
Junya
J
Terasawa
Yosuke
Y
Umehara
Norio
N
Suganuma
Masayoshi
M
Kawaguchi
Ryo
R
Ohtomo
D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics; D005020:Ethyl Methanesulfonate / Q000633:toxicity; D015966:Gene Expression Regulation, Fungal; D018506:Gene Expression Regulation, Plant; D054884:Host-Pathogen Interactions / Q000235:genetics; D025301:Hyphae / Q000235:genetics / Q000502:physiology; D000070116:Lotus / Q000235:genetics* / Q000382:microbiology; D059128:Mesorhizobium / Q000502:physiology / Q000648:ultrastructure; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000187:drug effects; D009153:Mutagens / Q000633:toxicity; D009154:Mutation; D038821:Mycorrhizae / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D055170:Plant Root Nodulation / Q000235:genetics; D018517:Plant Roots / Q000235:genetics / Q000382:microbiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053204:Root Nodules, Plant / Q000235:genetics* / Q000382:microbiology; D013559:Symbiosis
D009153:Mutagens; D005020:Ethyl Methanesulfonate
Arbuscular mycorrhizal fungi; EMS; Lotus japonicus; Symbiotic mutants