• Plant Phosphate Transporter 1 (PHT1) proteins, probably the only influx transporters for phosphate (Pi) uptake, are partially degraded on sufficient Pi levels to prevent excessive Pi accumulation. Therefore, the basal/constitutive expression level of PHT1 genes is vital for maintaining Pi uptake under Pi‐replete conditions.
• Rice (Oryza sativa) OsPHT1;1 is a unique gene as it is highly expressed and not responsive to Pi, however the mechanism for maintaining its basal/constitutive expression remains unknown. Using biochemical and genetic approaches, we identified and functionally characterised the transcription factors maintaining the basal/constitutive expression of OsPHT1;1.
• OsWRKY21 and OsWRKY108 interact within the nucleus and both bind to the W‐box in the OsPHT1;1 promoter. Overexpression of OsWRKY21 or OsWRKY108 led to increased Pi accumulation, resulting from elevated expression of OsPHT1;1. By contrast, oswrky21 oswrky108 double mutants showed decreased Pi accumulation and OsPHT1;1 expression in a Pi‐dependent manner. Moreover, similar to ospht1;1 mutants, plants expressing the OsWRKY21–SRDX fusion protein (a chimeric dominant suppressor) were impaired in Pi accumulation in Pi‐replete roots, accompanied by downregulation of OsPHT1;1 expression.
• Our findings demonstrated that rice WRKY transcription factors function redundantly to promote Pi uptake by activating OsPHT1;1 expression under Pi‐replete conditions, and represent a novel pathway independent of the central Pi signalling system.

中文翻译：

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OsWRKY21 和 OsWRKY108 在磷酸盐充足的条件下通过维持 OsPHT1;1 的组成型表达来重复促进磷酸盐的积累。

• 植物磷酸盐转运蛋白 1 (PHT1) 蛋白可能是唯一用于吸收磷酸盐 (Pi) 的流入转运蛋白，在足够的 Pi 水平下会部分降解，以防止过多的 Pi 积累。因此，PHT1 基因的基础/组成型表达水平对于在 Pi 充足条件下维持 Pi 摄取至关重要。
• 水稻 ( Oryza sativa ) OsPHT1;1是一个独特的基因，因为它高度表达且对 Pi 无反应，但维持其基础/组成型表达的机制仍然未知。使用生化和遗传方法，我们鉴定了维持OsPHT1;1基础/组成型表达的转录因子并对其进行功能表征。
• OsWRKY21 和 OsWRKY108 在细胞核内相互作用，都与OsPHT1;1启动子中的 W-box 结合。OsWRKY21或OsWRKY108的过表达导致 Pi 积累增加，这是由于OsPHT1;1的表达升高所致。相比之下，oswrky21 oswrky108双突变体显示出 Pi 积累减少和OsPHT1;1以 Pi 依赖性方式表达。此外，与ospht1;1突变体类似，表达 OsWRKY21-SRDX 融合蛋白（一种嵌合显性抑制因子）的植物在 Pi 富集根中的 Pi 积累受损，同时OsPHT1;1表达下调。
• 我们的研究结果表明，水稻 WRKY 转录因子通过在 Pi 充足条件下激活OsPHT1;1表达而发挥冗余功能以促进 Pi 吸收，并代表了一种独立于中央 Pi 信号系统的新途径。