The type Ⅲ effector NopL interacts with GmREM1a and GmNFR5 to promote symbiosis in soybean

The establishment of symbiotic interactions between leguminous plants and rhizobia requires complex cellular programming activated by Rhizobium Nod factors (NFs) as well as type III effector (T3E)-mediated symbiotic signaling. However, the mechanisms by which different signals jointly affect symbiosis are still unclear. Here we describe the mechanisms mediating the cross talk between the Sinorhizobium fredii T3E Nodulation Outer Protein L (NopL) effector and NF signaling in soybean. NopL physically interacts with the Glycine max Remorin 1a (GmREM1a) and the NFs receptor NFR5 (GmNFR5) and promotes GmNFR5 recruitment by GmREM1a. Furthermore, NopL and NF influence the expression of GmRINRK1, a receptor-like kinase (LRR-RLK) ortholog of the Lotus RINRK1, that mediates NF signaling. Taken together, our work indicates that S. fredii NopL can interact with the NF signaling cascade components to promote the symbiotic interaction in soybean. For the RNA-seq experiment, two types of soybean plants were used: the DN50 (wild type) and derived Gmrem1 mutant. These plants were inoculated with different strains of rhizobia, including the wild type HH103, derived mutants HH103ΩnopL and HH103ΩnodA and a mock control using 10mM MgSO4. The plants were inoculated with these rhizobia strains, and the roots were sampled, and total RNA was isolated at 1 dpi. The RNA-seq analysis was performed on the isolated total RNA from the roots of the different soybean plants under the various treatments. Rhizobia inoculation and sample collection were performed as described above. Three roots from different plants were collected as one replicate, and three biological replicates were collected for each treatment. Three individual samples were sequenced using Illumina NovaSeq 6000. To identify differential expression genes (DEGs) between two different samples, the expression level of each transcript was calculated according to the transcripts per million reads (TPM) method. RSEM was used to quantify gene abundances. Essentially, differential expression analysis was performed using the DESeq2. DEGs with |log2FC|≧1 and FDR≤ 0.05 were considered to be significantly different expressed genes.