Lipochitooligosaccharides (LCOs) are molecules secreted by rhizobia during the establishment of rhizobia-legume N2-fixing symbiosis. Some recent reports have shown that there are physiological effects on host and non-host rhizobia after LCO treatment. However, the cellular mechanisms underlying these observations are not known. Therefore, the study was aimed at assessing phenotypic changes by measuring photosynthesis, leaf area and dry weight on a non-host plant (tobacco). Our results did not show any significant physiological changes following LCO treatment. We also wanted to explore the molecular basis of changes in the plant cell by looking at gene and protein profiling following LCO treatment in a natural host plant (soybean) using real-time RT-PCR and SDS-PAGE. To do so, a reproducible stimulation method for soybean seed germination by LCO was successfully developed. The results obtained on soybean did not reveal significant differences in gene expression between water and LCO-treated seeds for the genes cdc2, WASI, ICL1 and 14-3-3 studied. In addition, LCO treatment did not change the protein profile compared to the water control in a significant way.

In this study, lipo-chitooligosaccharide (NodBj-V (C 18:1, MeFuc); LCO) 10-7M, extracted from Bradyrhizobium japonicum, was sprayed on the leaves of soybean cv. OAC Bayfield soybean and Evans x L66-2470 (carrying the rj1 mutation, and unable to nodulate). Leaf SA level and activities of the PR proteins chitinase, beta-1,3-glucanase and guaiacol peroxidase (GPOX) were quantified. Phenylalanine ammonia-lyase 1 (PAL1) and isoflavone synthase 2 (IFS2) relative gene expression levels in the sprayed leaves were quantified using quantitative real-time PCR. Messenger RNA abundance was quantified using microarrays. The treatment caused a transient increase in local salicylate levels 24 h after exposure, and a systemic increase in GPOX activity 48 h after exposure, in both soybean types. Of the selected 38 genes affected by the LCO treatment, 25 were stress-related. There were no significant differences in (A) chitinase and beta-1,3-glucanase activity, or (B) in PAL1 and IFS2 gene expression.

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