Effect of phytochrome-mediated red light signaling on phosphorus uptake and accumulation in rice

Phosphorus (P) is a macronutrient essential for plant growth and productivity. Plants uptake P as inorganic phosphate (Pi); however, in the natural ecosystem, Pi availability is frequently a severe limiting factor for plant growth. Thus, plants have evolved several mechanisms, such as the expression of Pi starvation-responsive genes, to adapt to Pi deficient conditions. Although we recently reported that phytochrome (Phy)-mediated red light signaling promotes Pi uptake by increasing expression levels of such genes in the model plant Arabidopsis, it remains elusive whether a similar mechanism exists in agricultural crops. In the present study, we analyzed the effects of red light signaling on Pi uptake in rice (<i>Oryza sativa</i> L.) using <i>osphyA</i> and <i>osphyB</i> single mutants, and the <i>osphyA osphyB</i> double mutant. Unlike <i>osphyA</i> seedlings, <i>osphyB</i> seedlings showed a reduction in Pi uptake and Pi content. Furthermore, illumination of wild-type seedlings with red light significantly promoted Pi uptake, whereas illumination with blue or far-red light did not. The <i>osphyB</i> mutant showed reduced expression levels of several Pi starvation-responsive genes including Pi transporter genes. Additionally, these phenotypes of <i>osphyB</i> knockout mutants were much more evident under Pi deficient conditions than under Pi sufficient conditions. Moreover, red light promoted Pi uptake in seedlings of other plant species including broccoli (<i>Brassica oleracea</i> L. var. <i>italica</i>) and lettuce (<i>Latuca sativa</i> L.). These results suggest that OsPhyB-mediated red light signaling promotes Pi uptake in rice by up-regulating the expression of Pi starvation response-associated genes, and this phenomenon may be conserved in a wide range of plant species.