SPL9 Modulates Nodulation under Nitrate Sufficiency Condition in .

Nodulation in spp. is induced by common environmental cues, such as low nitrogen availability conditions, in the presence of the specific spp. in the rhizosphere. (alfalfa) is an important nitrogen-fixing forage crop that is widely cultivated around the world and relied upon as a staple source of forage in livestock feed. Although alfalfa's relationship with these bacteria is one of the most efficient between rhizobia and legume plants, breeding for nitrogen-related traits in this crop has received little attention. In this report, we investigate the role of Squamosa-Promoter Binding Protein-Like 9 (SPL9), a target of miR156, in nodulation in alfalfa. Transgenic alfalfa plants with -silenced (-RNAi) and overexpressed () were compared to wild-type (WT) alfalfa for phenotypic changes in nodulation in the presence and absence of nitrogen. Phenotypic analyses showed that silencing of in alfalfa caused an increase in the number of nodules. Moreover, the characterization of phenotypic and molecular parameters revealed that regulates nodulation under a high concentration of nitrate (10 mM KNO) by regulating the transcription levels of the nitrate-responsive genes (), , (), and a shoot-controlled autoregulation of nodulation (AON) gene, (). While overexpressing transgenic plants have dramatically increased transcript levels of , , , and , reducing caused downregulation of these genes and displayed a nitrogen-starved phenotype, as downregulation of the transcript levels caused a nitrate-tolerant nodulation phenotype. Taken together, our results suggest that regulates nodulation in alfalfa in response to nitrate.