Transcriptomic and photosynthetic responses to grafting of the Nod1 gene in nodulated and non-nodulated soybeans

Legume plants form symbiotic relationships with rhizobia to convert N2 into ammonia, and the nodulation status can affect plant development including photosynthesis. However, the relationship between nitrogen fixation and photosynthesis during carbon and nitrogen metabolism remains unclear. This study was undertaken to unravel regulation of nodulation and photosynthesis using a spontaneous nonnodulated soybean mutant by grafting. The results of inheritance and gene mapping showed that the nonnodulated mutant was controlled by a recessive gene overlapped with the reported rj1 locus, and might be a new rj1 allele with 1 bp deletion in the fourth exon in comparison to the sequence of normal nodulation plants. According to grafting results, soybean nodulation is obviously determined by the roots, not the seedlings. Moreover, nitrogen content along with related metabolic enzyme activity, and photosynthetic capacity were enhanced by nonnodulated scions grafted with nodulated roots. Contrary results were obtained for nodulated scions grafted with nonnodulated roots. A total of 853 differentially expressed genes (DEGs) in the leaves and 1874 in the roots were identified by transcriptome analyses of the grafting treatments. We identified 285 differential gene ontology (GO) terms and 57 differential pathway terms identified in the leaves, while 856 differential GO terms and 207 differential pathway terms in the roots. Twenty DEGs interacting at translation level were selected, and the results of transcriptome analyses were verified by q-PCR. These findings indicated that the nodulation-related Nod allelic gene increases the nitrogen content of nonnodulated plants, which affects the enzymes involved in nitrogen metabolism, leading to changes in hormone levels and further regulation of photosynthesis and carbon metabolism.