Phosphorus (P), which is taken up by plants as inorganic phosphate (Pi), is one of the most important macronutrients for plant growth and development. Meanwhile, it determines plant architecture in several ways, including leaf inclination. However, the molecular basis underlying the crosstalk between the signaling pathways of plant P homeostasis and architecture maintenance remains elusive. We recently characterized a WRKY transcription factor, OsWRKY108, in rice (Oryza sativa). It functions redundantly with OsWRKY21 to promote Pi uptake in response to Pi supply. Overexpression of either OsWRKY108 or OsWRKY21 led to up-regulation of Pi transporter genes and thus enhanced Pi accumulation. By contrast, transgenic rice plants expressing OsWRKY21-SRDX (a fusion protein transforming OsWRKY21 from an activator into a dominant repressor) but not the OsWRKY108-SRDX fusion showed decreased Pi accumulation under Pi-replete conditions. Here, we report that OsWRKY108 acts as a positive regulator of leaf inclination. OsWRKY108 overexpressors showed increased leaf inclination and OsWRKY108-SRDX plants showed an erect-leaf phenotype, irrespective of the Pi regimes. Nevertheless, the response of leaf inclination to Pi starvation was largely impaired upon OsWRKY108 overexpression. Moreover, in both OsWRKY108-SRDX plants and OsWRKY108 overexpressors, the 'percentage of leaf angle alteration relative to wild-type' under Pi-starvation condition was more significant than that under Pi-replete condition. These results suggest that the regulation of OsWRKY108 on leaf inclination is in part dependent on Pi availability. Altogether, our findings demonstrate that OsWRKY108 is an integrative regulator of P homeostasis and leaf inclination, serving as a link between plant nutrient signaling and developmental cues.
Keywords: Phosphorus homeostasis; leaf inclination/erectness; phosphate uptake; wrky transcription factor.