Responses of a Model Legume Lotus japonicus to Lipochitin Oligosaccharide Nodulation Factors Purified from Mesorhizobium loti JRL501

Abstract

Lotus japonicus has been proposed as a model legume for molecular genetic studies of symbiotic plant-microbe interactions leading to the fixation of atmospheric nitrogen. Lipochitin oligosaccharides (LCOs), or Nod factors, were isolated from the culture of Mesorhizobium loti strain JRL501 (MAFF303099), an efficient microsymbiont of L. japonicus B-129 cv. Gifu. High-performance liquid chromatography and mass spectrometric analyses allowed us to identify at least five different structures of LCOs that were produced by JRL501. The major component was NodMl-V(C18:1, Me, Cb, AcFuc), an N-acetyl-glucosamine pentamer in which the nonreducing residue is N-acylated with a C18:1 acyl moiety, N-methylated, and carries a carbamoyl group and the reducing N-acetylglucosamine residue is substituted with 4-O-acetyl-fucose. Additional novel LCO structures bearing fucose instead of acetyl-fucose at the reducing end were identified. Mixtures of these LCOs could elicit abundant root hair deformation on L. japonicus roots at a concentration of 10(-7) to 10(-9) M. Spot inoculation of a few nanograms of LCOs on L. japonicus roots induced the formation of nodule primordia in which the early nodulin genes, ENOD40 and ENOD2, were expressed in a tissue-specific manner. We also observed the formation of a cytoplasmic bridge (preinfection thread) in the swollen outermost cortical cells. This is the first description of cytoplasmic bridge formation by purified LCOs alone in a legume-forming determinate nodules.

Positive and negative regulation of cortical cell division during root nodule development in Lotus japonicus is accompanied by auxin response

“…After rhizobial colonization of developing nodules, the accumulation of auxin becomes restricted to the region surrounding the infected cells. This region appears to correspond to the nodule parenchyma, which has previously been reported to show expression of organ differentiation markers such as ENOD2 (van de Wiel et al, 1990;Niwa et al, 2001). As the size of a determinate nodule continues to increase by cell proliferation and elongation even after differentiation, it is likely that the meristematic activities are maintained within the nodule.…”

Discriminative Phytoalexin Accumulation inLotus japonicusagainst Symbiotic and Non-Symbiotic Microorganisms and Related Chemical Signals

“…12) In L. japonicus, NF (10 nM) and chitin oligomers (dimer to octamer, about 100 mM) caused immediate (1 h) transcriptional activation of genes encoding enzymes of the phytoalexin pathway. 12) In the present study, high concentrations (1 and 10 mM) M. loti NF 12,13) caused the accumulation of small amounts of vestitol (about half level of GSH treatment) in a concentration-dependent manner, but lower concentrations (1 and 10 nM, still enough to initiate a symbiotic response) failed to induce phytoalexin accumulation (Fig. 2D).…”

NUCLEOPORIN85 Is Required for Calcium Spiking, Fungal and Bacterial Symbioses, and Seed Production in Lotus japonicus

“…After 24 h, seedlings with abnormal growth were removed and plates were placed in an incubator for another 24 h. The seedlings, which then had an average 7-mm taproot length, were used for analysis. Nod factor was purified from M. loti harboring pMP2112 according to the method described by Niwa et al (2001) and dissolved in distilled water (10 À6 M). The nod factor was diluted to 10 À8 M with half strength strength of B&D solution and was gently applied to 2-d-old seedlings to avoid disturbing root hairs.…”