Phosphorus is an essential nutrient for plants. It is stored as inorganic phosphate (Pi) in the vacuoles of land plants but as inorganic polyphosphate (polyP) in chlorophyte algae. Although it is recognized that the SPX-Major Facilitator Superfamily (MFS) and VPE proteins are responsible for Pi influx and efflux, respectively, across the tonoplast in land plants, the mechanisms that underlie polyP homeostasis and the transition of phosphorus storage forms during the evolution of green plants remain unclear. In this study, we showed that CrPTC1, encoding a protein with both SPX and SLC (permease solute carrier 13) domains for Pi transport, and CrVTC4, encoding a protein with both SPX and vacuolar transporter chaperone (VTC) domains for polyP synthesis, are required for vacuolar polyP accumulation in the chlorophyte Chlamydomonas reinhardtii. Phylogenetic analysis showed that the SPX-SLC, SPX-VTC, and SPX-MFS proteins were present in the common ancestor of green plants (Viridiplantae). The SPX-SLC and SPX-VTC proteins are conserved among species that store phosphorus as vacuolar polyP and absent from genomes of plants that store phosphorus as vacuolar Pi. By contrast, SPX-MFS genes are present in the genomes of streptophytes that store phosphorus as Pi in the vacuoles. These results suggest that loss of SPX-SLC and SPX-VTC genes and functional conservation of SPX-MFS proteins during the evolution of streptophytes accompanied the change from ancestral polyP storage to Pi storage.

磷是植物必需的营养元素。它作为无机磷酸盐 (Pi) 储存在陆生植物的液泡中，但作为无机多磷酸盐 (polyP) 储存在叶绿藻中。尽管已经认识到 SPX 主要促进剂超家族 (MFS) 和 VPE 蛋白分别负责通过陆地植物液泡膜的 Pi 流入和流出，但在进化过程中构成 polyP 稳态和磷储存形式转变的机制绿色植物的数量仍不清楚。在这项研究中，我们展示了CrPTC1编码的蛋白质，该蛋白质具有用于 Pi 转运的 SPX 和 SLC（通透酶溶质载体 13）结构域，以及CrVTC4，编码具有用于 polyP 合成的 SPX 和液泡转运蛋白伴侣 (VTC) 域的蛋白质，是叶绿体莱茵衣藻中液泡 polyP 积累所必需的. 系统发育分析表明，SPX-SLC、SPX-VTC 和 SPX-MFS 蛋白存在于绿色植物（Viridiplantae）的共同祖先中。SPX-SLC 和 SPX-VTC 蛋白在将磷储存为液泡聚磷的物种中是保守的，而在将磷储存为液泡聚磷的植物基因组中不存在。相比之下，SPX-MFS 基因存在于将磷作为 Pi 储存在液泡中的链霉菌基因组中。这些结果表明，在链霉菌进化过程中，SPX-SLC 和 SPX-VTC 基因的丢失和 SPX-MFS 蛋白的功能保守性伴随着从祖先 polyP 储存到 Pi 储存的变化。