Medicago truncatula NIN is essential for rhizobial-independent nodule organogenesis induced by autoactive calcium/calmodulin-dependent protein kinase.
The symbiotic association between legumes and nitrogen-fixing bacteria collectively known as rhizobia results in the formation of a unique plant root organ called the nodule. This process is initiated following the perception of rhizobial nodulation factors by the host plant. Nod factor (NF)-stimulated plant responses, including nodulation-specific gene expression, is mediated by the NF signaling pathway. Plant mutants in this pathway are unable to nodulate. We describe here the cloning and characterization of two mutant alleles of the Medicago truncatula ortholog of the Lotus japonicus and pea (Pisum sativum) NIN gene. The Mtnin mutants undergo excessive root hair curling but are impaired in infection and fail to form nodules following inoculation with Sinorhizobium meliloti. Our investigation of early NF-induced gene expression using the reporter fusion ENOD11::GUS in the Mtnin-1 mutant demonstrates that MtNIN is not essential for early NF signaling but may negatively regulate the spatial pattern of ENOD11 expression. It was recently shown that an autoactive form of a nodulation-specific calcium/calmodulin-dependent protein kinase is sufficient to induce nodule organogenesis in the absence of rhizobia. We show here that MtNIN is essential for autoactive calcium/calmodulin-dependent protein kinase-induced nodule organogenesis. The non-nodulating hcl mutant has a similar phenotype to Mtnin, but we demonstrate that HCL is not required in this process. Based on our data, we suggest that MtNIN functions downstream of the early NF signaling pathway to coordinate and regulate the correct temporal and spatial formation of root nodules.
Marsh
John F
JF
John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom. john.marsh@bbsrc.ac.uk
Rakocevic
Alexandra
A
Mitra
Raka M
RM
Brocard
Lysiane
L
Sun
Jongho
J
Eschstruth
Alexis
A
Long
Sharon R
SR
Schultze
Michael
M
Ratet
Pascal
P
Oldroyd
Giles E D
GE
D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism / Q000502:physiology*; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D005966:Glucuronidase / Q000032:analysis; D046913:Medicago truncatula / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism / Q000382:microbiology; D009154:Mutation; D009586:Nitrogen Fixation; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000032:analysis; D053204:Root Nodules, Plant / Q000254:growth & development* / Q000378:metabolism / Q000382:microbiology; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D016962:Sinorhizobium meliloti / Q000502:physiology; D013559:Symbiosis
D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D005966:Glucuronidase