Phloem-Mobile Negatively Regulates Expression of in Arabidopsis Roots.

Phosphorus (P) is an essential plant macronutrient; however, its availability is often limited in soils. Plants have evolved complex mechanisms for efficient phosphate (Pi) absorption, which are responsive to changes in external and internal Pi concentration, and orchestrated through local and systemic responses. To explore these systemic Pi responses, here we identified as a phloem-mobile mRNA, an Arabidopsis homolog of , that is responsive to the Pi-starvation stress. qRT-PCR assays revealed that was up-regulated and expressed in both shoot and root in response to Pi-starvation stress. The mutant displayed higher shoot and root biomass compared to wild-type plants, under Pi-starvation conditions. Interestingly, the expression of () and was enhanced in in response to a Pi-starvation treatment. A split-root assay showed that expression was systemically regulated under Pi-starvation conditions, and in , systemic controls on and expression were moderately disrupted. Heterografting assays confirmed graft transmission of transcripts, and and expression was decreased in heterografted rootstocks. Taken together, our findings support the hypothesis that mobile mRNA serves as a long-distance Pi response signal, which negatively regulates Pi transport and utilization in Arabidopsis.