Phosphorus-Use-Efficiency Gene Identification in Fabaceae and RSL2 Expansion in Lupinus albus Is Associated with Low-Phosphorus Adaptation

Phosphorus is critical for plant growth but often becomes less accessible due to its precipitation with cations in soil. Fabaceae, a diverse plant family, exhibits robust adaptability and includes species like <i>Lupinus albus</i>, known for its efficient phosphorus utilization via cluster roots. Here, we systematically identified phosphorus-utilization-efficiency (PUE) gene families across 35 Fabaceae species, highlighting significant gene amplification in PUE pathways in Fabaceae. Different PUE pathways exhibited variable amplification, evolution, and retention patterns among various Fabaceae crops. Additionally, the number of homologous genes of the root hair development gene <i>RSL2</i> in <i>L. albus</i> was far more than that in other Fabaceae species. Multiple copies of the <i>RSL2</i> gene were amplified and retained in <i>L. albus</i> after whole genome triplication. The gene structure and motifs specifically retained in <i>L. albus</i> were different from homologous genes in other plants. Combining transcriptome analysis under low-phosphorus treatment, it was found that most of the homologous genes of <i>RSL2</i> in <i>L. albus</i> showed high expression in the cluster roots, suggesting that the <i>RSL2</i> gene family plays an important role in the adaptation process of <i>L. albus</i> to low-phosphorus environments and the formation of cluster roots.