Transcriptomic Comparison of Soybean Roots Inoculated with Different Rhizobium Strains During Early Symbiosis.

Area of Science:

• Plant-Microbe Interactions
• Molecular Biology
• Agricultural Science

Background:

• Soybean-rhizobia symbiosis is crucial for sustainable agriculture, enhancing nitrogen fixation and crop yields.
• Limited comparative studies exist on host gene expression regulated by different rhizobial strains.
• Understanding strain-specific interactions is key to improving symbiotic nitrogen fixation (SNF).

Purpose of the Study:

• To comparatively analyze host gene expression regulated by *Bradyrhizobium ottawaense* Bott 59 and *Bradyrhizobium diazoefficiens* USDA 110.
• To identify conserved and strain-specific molecular responses in soybean roots during early symbiosis.
• To provide transcriptomic resources for improving crop nodulation and nitrogen fixation efficiency.

Main Methods:

• Comparative inoculation of soybean with *B. ottawaense* Bott 59 and *B. diazoefficiens* USDA 110.
• Evaluation of symbiotic phenotypes (nodule number, nitrogenase activity, biomass) at 21 days post-inoculation (dpi).
• Root transcriptomic analysis at 3 dpi to assess early molecular responses.

Main Results:

• Bott 59 inoculation resulted in superior nodule number, nitrogenase activity, and biomass compared to USDA 110.
• Conserved host responses included NIN-mediated signaling, AON signaling, and phenylpropanoid/brassinosteroid biosynthesis.
• Bott 59 specifically induced isoflavonoid/flavonoid biosynthesis genes and triggered broader reprogramming in hormone signaling pathways.

Conclusions:

• *B. ottawaense* Bott 59 demonstrates enhanced symbiotic performance over USDA 110 in soybean.
• The study elucidates conserved and strain-specific transcriptional events in host-rhizobia interactions.
• Findings offer insights into SNF mechanisms and resources for genetic improvement of crop symbiosis.