Krupinska Karin, Frank Susann, Boschian Luca, Saeid Nia Monireh, Braun Susanne, Schäfer Anke, Voigt Ulrike, Niewiadomska Ewa, Hause Bettina, Hensel Götz, Bilger Wolfgang
Institute of Botany, Christian-Albrechts-University (CAU), Kiel, Germany.
The Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Niezapominajek 21, 30-239, Krakow, Poland.
Planta. 2025 Jun 17;262(2):32. doi: 10.1007/s00425-025-04736-8.
The DNA-binding protein WHIRLY1, sharing structural similarities with ferritin, plays a role in the formation of iron cofactor proteins within chloroplasts. Previous studies indicated that barley plants with a knockdown of HvWHIRLY1 containing a minimal amount of the protein are compromised in chloroplast development and photosynthesis, and get chlorotic leaves when grown at high irradiance. Thereby, the leaves display signs of iron deficiency. Metal determination revealed, however, that leaves of WHIRLY1-deficient plants had a regular iron content. Nevertheless, WHIRLY1-deficiency affected the functionality of photosystem II less than that of photosystem I, which has a higher demand for iron. Immunological analyses revealed that components of both photosystems had reduced levels. Additionally, the levels of other chloroplast proteins containing different classes of iron cofactors were lower in the WHIRLY1-deficient plants compared to the wild type. In contrast, the level of the iron sequestering protein ferritin increased in WHIRLY1-deficient lines, whereby high irradiance intensified this effect. RNA analyses showed that the upregulation of ferritin coincided with an enhanced expression of the corresponding gene, reflecting an apparent overload of chloroplasts with free iron. Ferritin and WHIRLY proteins are known to share the same oligomeric structure. Therefore, the high abundance of ferritin in WHIRLY1-deficient plants might be a compensation for the reduced abundance of WHIRLY1. Enhanced expression levels of genes encoding photosynthesis proteins and iron cofactor proteins indicate a demand for protein formation or assembly of protein complexes. The results support a general role of WHIRLY1 in assembly and/or stabilization of chloroplast proteins and, moreover, suggest a specific function in sequestering and supply of iron in chloroplasts.
DNA结合蛋白WHIRLY1与铁蛋白在结构上有相似之处，在叶绿体中铁辅因子蛋白的形成过程中发挥作用。先前的研究表明，HvWHIRLY1基因敲低的大麦植株中该蛋白含量极少，其叶绿体发育和光合作用受到损害，在高光照条件下生长时叶片会出现黄化现象。因此，叶片表现出缺铁的迹象。然而，金属含量测定显示，缺乏WHIRLY1的植株叶片铁含量正常。尽管如此，WHIRLY1的缺乏对光系统II功能的影响小于对光系统I的影响，因为光系统I对铁的需求更高。免疫分析表明，两个光系统的组分水平都有所降低。此外，与野生型相比，缺乏WHIRLY1的植株中其他含有不同类铁辅因子的叶绿体蛋白水平较低。相反，在缺乏WHIRLY1的株系中，铁螯合蛋白铁蛋白的水平升高，高光照会增强这种效应。RNA分析表明，铁蛋白的上调与相应基因表达的增强同时出现，这反映出叶绿体中游离铁明显过量。已知铁蛋白和WHIRLY蛋白具有相同的寡聚结构。因此，缺乏WHIRLY1的植株中铁蛋白含量高可能是对WHIRLY1含量降低的一种补偿。编码光合作用蛋白和铁辅因子蛋白的基因表达水平提高，表明对蛋白质形成或蛋白质复合物组装有需求。这些结果支持了WHIRLY1在叶绿体蛋白组装和/或稳定中的普遍作用，此外，还表明其在叶绿体中铁的螯合和供应方面具有特定功能。
