Fatty Acid Desaturases GmROD1s Are Involved in Nodulation by Regulating the Flux of Polyunsaturated Fatty Acids

Legume-rhizobia symbiosis requires induction of fatty acid (FA) biosynthesis, especially the polyunsaturated fatty acids (PUFAs), as essential lipid and membrane components for nodulation. However, the regulation of PUFA homoeostasis remains poorly understood. Direct molecular and genetic evidence linking specific FA desaturation enzymes to this process is limited. Here, we investigated two soybean FA desaturation genes, GmROD1a/b, and provided their previously unrecognised roles in nodulation. Both were strongly induced during early rhizobial infection and remained highly expressed throughout nodule development. Overexpression significantly enhanced nodulation and plant growth, whereas disruption reduced nodule numbers. Transcriptomic analyses further revealed that GmROD1s promote PUFA accumulation and regulate genes associated with nodulation and nodule function, energy metabolism, membrane biogenesis, etc. We also identified two members of the WRINKLED family of transcription factors that are co-expressed with GmROD1 in rhizobia-infected roots and nodules. Further, promoter binding and transcription activation assays confirmed that GmWRI1 and the newly identified nodulation-associated factor, GmWRI3, directly promote GmROD1a/b expression, and overexpression of either transcription factor in soybean hairy roots significantly promoted nodulation. Together, our study uncovers a previously unappreciated role of ROD1 in nodulation, extending the functional role beyond FA desaturation. More importantly, we provide new molecular evidence linking nodulation to PUFA biosynthesis mediated by a previously unappreciated GmWRI1/3-GmROD1a/b regulatory module. Notably, the biological function of GmWRI3 in soybean has not been experimentally characterised. These findings establish a mechanistic connection between fatty acid metabolism and nodulation, offering potential targets for improving legume crop yields.