Shaikh Kashif Mohd, Walker Charlotte E, Tóth Dávid, Kuntam Soujanya, Polgár Tamás F, Petrova Nia Z, Garland Herbie, Mackinder Luke C M, Tóth Szilvia Z, Spetea Cornelia
Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg 40530, Sweden.
Institute of Plant Biology, HUN-REN Biological Research Centre, Szeged, Szeged H-6726, Hungary.
Plant Physiol. 2025 Apr 30;198(1). doi: 10.1093/plphys/kiaf158.
Phosphate (Pi) is essential for photosynthesis in the chloroplast of algae and plants. Pi homeostasis in the chloroplast is maintained by transporters from several families, whose identities in algae are largely unknown as compared with land plants. Here, we assess the role of the putative PHOSPHATE TRANSPORTER 4-9 from Chlamydomonas reinhardtii (CrPHT4-9) in maintaining chloroplast Pi homeostasis and modulating photosynthesis. Based on phylogenetic analyses and heterologous expression in a yeast (Saccharomyces cerevisiae) strain lacking Pi transporters, we demonstrate that CrPHT4-9 is a Pi transporter closely related to the chloroplast members of the PHT4 family in Arabidopsis (Arabidopsis thaliana). CrPHT4-9 is localized within the chloroplast, more specifically in the thylakoid membrane network and the tubules traversing the CO2-fixing pyrenoid. Two mutants lacking CrPHT4-9 (Crpht4-9) exhibit defective photoautotrophic growth, altered cell morphology and chloroplast ultrastructure under CO2-limiting conditions. In the Crpht4-9 mutants, we further show an increased proton motive force across the thylakoid membrane, enhanced energy- and state-transition-dependent non-photochemical quenching of chlorophyll a fluorescence, and diminished photosynthetic electron transport and ATP synthase activity. The Crpht4-9 mutants exhibit reduced affinity to inorganic carbon, indicating an impaired carbon-concentrating mechanism. These phenotypes are largely recovered by genetic complementation as well as by ample CO2 supply and, interestingly, by Pi deprivation. Therefore, we conclude that the thylakoid- and pyrenoid-localized CrPHT4-9 maintains Pi homeostasis within the chloroplast and is essential for photosynthesis and growth.
磷酸盐（Pi）对于藻类和植物叶绿体中的光合作用至关重要。叶绿体中的Pi稳态由几个家族的转运蛋白维持，与陆地植物相比，藻类中这些转运蛋白的身份在很大程度上尚不清楚。在这里，我们评估莱茵衣藻（Chlamydomonas reinhardtii）中假定的磷酸盐转运蛋白4-9（CrPHT4-9）在维持叶绿体Pi稳态和调节光合作用中的作用。基于系统发育分析以及在缺乏Pi转运蛋白的酵母（Saccharomyces cerevisiae）菌株中的异源表达，我们证明CrPHT4-9是一种与拟南芥（Arabidopsis thaliana）中PHT4家族的叶绿体成员密切相关的Pi转运蛋白。CrPHT4-9定位于叶绿体内，更具体地说是在类囊体膜网络和穿过固定CO2的淀粉核的小管中。两个缺乏CrPHT4-9（Crpht4-9）的突变体在CO2限制条件下表现出光合自养生长缺陷、细胞形态改变和叶绿体超微结构改变。在Crpht4-9突变体中，我们进一步表明跨类囊体膜的质子动力增加、叶绿素a荧光的能量和状态转换依赖性非光化学猝灭增强，以及光合电子传递和ATP合酶活性降低。Crpht4-9突变体对无机碳的亲和力降低，表明碳浓缩机制受损。这些表型在很大程度上通过遗传互补、充足的CO2供应以及有趣的是通过Pi剥夺得以恢复。因此，我们得出结论，定位于类囊体和淀粉核的CrPHT4-9维持叶绿体内的Pi稳态，并且对于光合作用和生长至关重要。
