Transcriptome analysis of the phosphate starvation response sheds light on strigolactone biosynthesis in rice

Phosphorus (P) is a major element required for plant growth and development. To cope with P shortage, plants activate local and long-distance signaling pathways, such as the increase in the production and exudation of strigolactones (SLs). The role of the latter in mitigating P deficiency is, however, still largely unknown. To shed light on this, we studied the transcriptional response to P starvation and replenishment in wild-type rice and a SL mutant, dwarf10 (d10), and upon exogenous application of the synthetic SL GR24. P starvation resulted in major transcriptional alterations, such as the upregulation of P TRANSPORTER, SYG1/PHO81/XPR1 (SPX) and VACUOLAR PHOSPHATE EFFLUX TRANSPORTER. Gene Ontology (GO) analysis of the genes induced by P starvation showed enrichment in phospholipid catabolic process and phosphatase activity. In d10, P deficiency induced upregulation of genes enriched for sesquiterpenoid production, secondary shoot formation, and metabolic processes, including lactone biosynthesis. Furthermore, several genes induced by GR24 treatment shared the same GO terms with P starvation-induced genes, such as oxidation reduction, heme binding and oxidoreductase activity, hinting at the role that SLs play in the transcriptional reprogramming upon P starvation. Gene co-expression network analysis uncovered a METHYL TRANSFERASE that displayed co-regulation with known rice SL biosynthetic genes. Functional characterization showed that this gene encodes an enzyme catalyzing the conversion of carlactonoic acid to methyl carlactonoate. Our work provides a valuable resource to further studies on the response of crops to P deficiency and reveals a tool for the discovery of new SL biosynthetic genes.