Genome-wide identification of genes associated with enhanced carbon secretion in cluster roots of Lupinus albus L.

Several plant species adapted to low-phosphorus (P) conditions develop cluster roots, specialized structures that release organic acids and acid phosphatases (APases) to enhance phosphate (Pi) availability. White lupin (Lupinus albus L.) is a model for studying cluster root function. Using a Positron Emission Tracer Imaging System (PETIS), we previously observed spot-like carbon secretion patterns, suggesting variation in secretion activity among cluster roots. In this study, we combined PETIS with RNA-Seq to investigate transcriptomic differences between cluster roots with varying secretion activity. We identified 327 positively and 53 negatively correlated genes with secretion levels. Among the positively correlated genes, we found three ALUMINUM-ACTIVATED MALATE TRANSPORTER (ALMT) genes, including LaALMT1, and two MULTI-DRUG AND TOXIC COMPOUND EXTRUSION (MATE) genes, likely involved in malate and citrate secretion, respectively. Two APase genes encoding putative secreted enzymes were also upregulated. While Pi transporter (PHT) genes showed stable expression, PHO1;6H was significantly upregulated in high carbon-secreting roots. Additionally, we identified four transcription factors potentially involved in organic acid transporter and APase gene expression. Our findings provide key genetic candidates involved in Pi mobilization, offering insights into plant adaptation to P deficiency.