Rearrangement of actin cytoskeleton mediates invasion of Lotus japonicus roots by Mesorhizobium loti.
Infection thread-dependent invasion of legume roots by rhizobia leads to internalization of bacteria into the plant cells, which is one of the salient features of root nodule symbiosis. We found that two genes, Nap1 (for Nck-associated protein 1) and Pir1 (for 121F-specific p53 inducible RNA), involved in actin rearrangements were essential for infection thread formation and colonization of Lotus japonicus roots by its natural microsymbiont, Mesorhizobium loti. nap1 and pir1 mutants developed an excess of uncolonized nodule primordia, indicating that these two genes were not essential for the initiation of nodule organogenesis per se. However, both the formation and subsequent progression of infection threads into the root cortex were significantly impaired in these mutants. We demonstrate that these infection defects were due to disturbed actin cytoskeleton organization. Short root hairs of the mutants had mostly transverse or web-like actin filaments, while bundles of actin filaments in wild-type root hairs were predominantly longitudinal. Corroborating these observations, temporal and spatial differences in actin filament organization between wild-type and mutant root hairs were also observed after Nod factor treatment, while calcium influx and spiking appeared unperturbed. Together with various effects on plant growth and seed formation, the nap1 and pir1 alleles also conferred a characteristic distorted trichome phenotype, suggesting a more general role for Nap1 and Pir1 in processes establishing cell polarity or polar growth in L. japonicus.
Yokota
Keisuke
K
Centre for Carbohydrate Recognition and Signalling, Department of Molecular Biology, University of Aarhus, 8000 Aarhus C, Denmark.
Fukai
Eigo
E
Madsen
Lene H
LH
Jurkiewicz
Anna
A
Rueda
Paloma
P
Radutoiu
Simona
S
Held
Mark
M
Hossain
Md Shakhawat
MS
Szczyglowski
Krzysztof
K
Morieri
Giulia
G
Oldroyd
Giles E D
GE
Downie
J Allan
JA
Nielsen
Mette W
MW
Rusek
Anna Maria
AM
Sato
Shusei
S
Tabata
Satoshi
S
James
Euan K
EK
Oyaizu
Hiroshi
H
Sandal
Niels
N
Stougaard
Jens
J
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000483:Alleles; D003001:Cloning, Molecular; D003599:Cytoskeleton / Q000378:metabolism*; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D000070116:Lotus / Q000235:genetics / Q000378:metabolism / Q000382:microbiology*; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012230:Rhizobiaceae / Q000254:growth & development*; D053204:Root Nodules, Plant / Q000166:cytology / Q000378:metabolism / Q000382:microbiology; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013559:Symbiosis
D000199:Actins; D018744:DNA, Plant; D010940:Plant Proteins