The Rhizobium tropici CIAT 899 NodD2 protein regulates the production of Nod factors under salt stress in a flavonoid-independent manner

Abstract

In the symbiotic associations between rhizobia and legumes, NodD promotes the expression of the nodulation genes in the presence of appropriate flavonoids. This set of genes is implied in the synthesis of Nodulation factors, which are responsible for launching the nodulation process. Rhizobium tropici CIAT 899 is the most successful symbiont of Phaseolus vulgaris and can nodulate a variety of legumes. This strain produces Nodulation factors under abiotic stress such as acidity or high concentration of salt. Genome sequencing of CIAT 899 allowed the identification of five nodD genes. Whereas NodD1 is essential to nodulate Leucaena leucocephala, Lotus japonicus and Macroptilium atropurpureum, symbiosis with P. vulgaris and Lotus burtii decreased the nodule number but did not abolish the symbiotic process when NodD1 is absent. Nodulation factor synthesis under salt stress is not regulated by NodD1. Here we confirmed that NodD2 is responsible for the activation of the CIAT 899 symbiotic genes under salt stress. We have demonstrated that NodD1 and NodD2 control the synthesis of the Nod factor necessary for a successful symbiosis with P. vulgaris and L. burtii. This is the first time that NodD is directly implied in the activation of the symbiotic genes under an abiotic stress.

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest

“… 13 The evaluation of in vitro environmental stresses are important to the selection of bacteria that are (likely) more tolerant and also to better understand the bacteria biology. 15 These features are particularly interesting to be evaluated in studies of rhizobia from tropical dry lands with low rainfall and high temperature averages.…”

Transcriptomic Studies of the Effect of nod Gene-Inducing Molecules in Rhizobia: Different Weapons, One Purpose

“…Interestingly, with respect to the cultures supplemented with salt, the same symbiotic-related genes are also upregulated, but many other non-symbiotic genes are also differentially expressed (95 upregulated and 628 downregulated) ( Table S3 ). Interestingly, in a second transcriptomic approach, del Cerro et al [ 45 ] confirmed that the transcriptional activation of previously mentioned genes upon apigenin and salt conditions are mediated by NodD1 and NodD2, respectively. Taking in consideration both transcriptomic studies, two groups of genes are identified: (i) genes controlled by nod boxes (NB); and (ii) genes not preceded by a NB ( Figure 4 ).…”

Identification of a gene encoding a sugar transporter as a potential target of a novel LysR‐type transcriptional regulator rluD from rhizobium required for symbiotic nodulation in soybean (Glycine max Merr.)

“…To our knowledge, a few LTTRs can function as activators or repressors involved in the symbiotic nodulation of rhizobia, although some genes regulate biosynthesis of metabolism to promote nodulation (Luo et al., ). Both NodD1 and NodD2 in Rhizobium tropici CIAT 899 control the entire NF synthesis and are necessary for successful symbiosis (Del Cerro et al., ). LsrA has been indicated in symbiosis and elicits only white nodules that exhibit no nitrogenase activity.…”