Symbiotic Rhizobium and Nitric Oxide Induce Gene Expression of Non-symbiotic Hemoglobin in Lotus japonicus

Abstract

We characterized the expression profiles of LjHb1 and LjHb2, non-symbiotic hemoglobin (non-sym-Hb) genes of Lotus japonicus. Although LjHb1 and LjHb2 showed 77% homology in their cDNA sequences, LjHb2 is located in a unique position in the phylogenetic tree of plant Hbs. The 5'-upstream regions of both genes contain the motif AAAGGG at a position similar to that in promoters of other non-sym-Hb genes. Expression profiles obtained by using quantitative RT-PCR showed that LjHb1 and LjHb2 were expressed in all tissues of mature plants, and expression was enhanced in mature root nodules. LjHb1 was strongly induced under both hypoxic and cold conditions, and by the application of nitric oxide (NO) donor, whereas LjHb2 was induced only by the application of sucrose. LjHb1 was also induced transiently by the inoculation with the symbiotic rhizobium Mesorhizobium loti MAFF303099. Observations using fluorescence microscopy revealed the induction of LjHb1 expression corresponded to the generation of NO. These results suggest that non-sym-Hb and NO have important roles in stress adaptation and in the early stage of legume-rhizobium symbiosis.

The exudate from an arbuscular mycorrhizal fungus induces nitric oxide accumulation in Medicago truncatula roots

“…The role of NO is much more obscure in symbiotic systems. On one hand, the transient NO generation observed in Lotus japonicus roots at 4 h after Mesorhizobium loti inoculation paralleled the enhanced expression of a nonsymbiotic hemoglobin gene LjHb1, possibly involved in NO detoxification (Shimoda et al 2005;Nagata et al 2008). These authors suggested the quick generation of NO to be the signal triggering NO-mediated defense responses in the host plant.…”

“…This suggests that early NO production is an AM-specific component of the plant response within the "common SYM pathway." Notably, Shimoda et al (2005) described NO production in L. japonicus roots 4 h after rhizobium inoculation; however, they did not test the effect of purified Nod factor and rather proposed rhizobial LPS as the candidate inducers of NO production (Nagata et al 2009). It will be interesting to evaluate whether the LCO recently identified as part of the fungal exudates of G. intraradices (Maillet et al 2011) are responsible for the induction of NO production.…”

“…NO production is also induced by basal elicitors of plant responses such as bacterial lipopolysaccharides (LPS) (Zeidler et al 2004). Finally, evidence of NO involvement in plant symbioses is emerging; the use of NO-specific fluorescent probes has shown the occurrence of NO accumulation in the early (Shimoda et al 2005;Nagata et al 2008;del Giudice et al 2011) and late stages of the nitrogen-fixing symbiosis (NFS) that legumes establish with rhizobia (Baudouin et al 2006;Pii et al 2007;Horchani et al 2011). In addition, the application of a specific NO scavenger to M. truncatula roots inoculated with rhizobia resulted in a significantly reduced number of nodules (Pii et al 2007;del Giudice et al 2011).…”

Nodules and oxygen

“…Baudouin et al (2006) have shown that NO is produced in rhizobia-containing cells of nodules of the legume Medicago truncatula. Consistent with their function of lowering internal NO levels, class I hemoglobins are formed in the infected cells of Lotus japonicus nodules (Uchiumi et al 2002;Shimoda et al 2005). The reconstitution of class I Hb after NO scavenging requires the oxidation of ascorbate ( Figure 1).…”

Model legumes contribute to faba bean breeding

“…170, 1052Sci. 170, -1058 Gallardo, K., Firnhaber, C., Zuber, H., Hericher, D., Belghazi, M., Henry, C., Küster,8 H., Thompson, R., 2007. A combined proteome and transcriptome analysis of 9…”