LIN, a novel type of U-box/WD40 protein, controls early infection by rhizobia in legumes.
The formation of a nitrogen-fixing nodule requires the coordinated development of rhizobial colonization and nodule organogenesis. Based on its mutant phenotype, lumpy infections (lin), LIN functions at an early stage of the rhizobial symbiotic process, required for both infection thread growth in root hair cells and the further development of nodule primordia. We show that spontaneous nodulation activated by the calcium- and calmodulin-dependent protein kinase is independent of LIN; thus, LIN is not necessary for nodule organogenesis. From this, we infer that LIN predominantly functions during rhizobial colonization and that the abortion of this process in lin mutants leads to a suppression of nodule development. Here, we identify the LIN gene in Medicago truncatula and Lotus japonicus, showing that it codes for a predicted E3 ubiquitin ligase containing a highly conserved U-box and WD40 repeat domains. Ubiquitin-mediated protein degradation is a universal mechanism to regulate many biological processes by eliminating rate-limiting enzymes and key components such as transcription factors. We propose that LIN is a regulator of the component(s) of the nodulation factor signal transduction pathway and that its function is required for correct temporal and spatial activity of the target protein(s).
Institute of Genetics, Biological Research Center, Szeged 6726, Hungary.
Ernö
E
Kiss
Boglárka
B
Oláh
Péter
P
Kaló
Monica
M
Morales
Anne B
AB
Heckmann
Andrea
A
Borbola
Anita
A
Lózsa
Katalin
K
Kontár
Patrick
P
Middleton
J Allan
JA
Downie
Giles E D
GE
Oldroyd
Gabriella
G
Endre
D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D000070116:Lotus / Q000201:enzymology / Q000235:genetics*; D046913:Medicago truncatula / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D055170:Plant Root Nodulation / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D013559:Symbiosis / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism
D018744:DNA, Plant; D010940:Plant Proteins; D044767:Ubiquitin-Protein Ligases; D017871:Calcium-Calmodulin-Dependent Protein Kinases