The Innovation Team of Soil-Plant Interactions at the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) has developed an efficient visualization technique to detect inorganic orthophosphate (Pi) in plant cells. They have also revealed a novel mechanism for regulating the distribution of Pi in plant cells. The research has been published in "Nature Plants".

Phosphorus (P) is an essential nutrient for plant growth and development. An adequate supply of P nutrients is essential for maintaining high productivity in various ecosystems, including forests, grasslands, and agricultural soils. However, P limitation is a widespread problem in different ecosystems worldwide, which has a major impact on global food security and ecological safety. Therefore, an important topic in vegetation ecology and plant nutrition is to understand the strategies and regulatory mechanisms for maintaining high plant productivity under P-limited conditions.

The primary P form absorbed by plant roots is Pi, which is also the major form that is recycled and utilized in plant cells. When P is sufficient, Pi can account for about 80% of the total P content in plants. Therefore, studying the cell distribution patterns, signal transduction, and homeostatic regulation of Pi in plants is crucial for understanding the mechanisms that maintain high productivity under P limitation. However, the distribution and storage of Pi between cells in plant tissues remains obscure, mainly due to the lack of efficient visualization techniques for Pi.

The IARRP team established an efficient visualization technique for the detection of Pi in plant cells, namely the Inorganic Orthophosphate Staining Assay (IOSA). Compared to existing techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for in situ distribution analysis of total phosphorus in plant tissues and Fluorescence Imaging Plate Reader Assay (FLIPPi) for the detection of cellular Pi using fluorescent protein-labeled laser scanning confocal microscopy, IOSA has numerous advantages. These include low cost, short processing time, simplicity, and no limitations regarding plant species or tissue forms. Using the IOSA technique, the researchers showed that Pi is mainly distributed in leaf mesophyll cells, root epidermis, exodermis, cortical sclerenchymatous cells, cortical parenchymal cells close to the endodermis, and endodermal cells in rice and Arabidopsis thaliana.

The study also revealed new functions of known P master regulatory factors, such as PHRs, PHO2, PHO1, and PHF1, in regulating the Pi distribution in plant cells. Using the IOSA technique, the research team screened a series of rice mutants with altered Pi intracellular distribution and cloned a gene of HPA1/OsPHO1;1, which regulates the uneven distribution of Pi from the leaf tip to the leaf base. This gene is highly expressed in the leaf companion cells of the vascular bundle and gradually decreases from the leaf tip to the leaf base. It mainly regulates the transport of Pi from the leaf tip cells to the leaf base through the phloem, effectively promoting the output and reuse of P in the leaf. In conclusion, this study opens new avenues for understanding the regulatory mechanisms of efficient P utilization by establishing an efficient technique for visualizing Pi in plant cells and exploring its potential applications.

The co-first authors of the paper are Dr. Meina-Guo (currently an associate professor at the College of Biological Sciences and Technology of Beijing Forestry University), Ph.D. Wenyuan-Ruan Ruili-Li, and Lei-Xu. Ph.D. Qianqian-Zhang and master student Jianhao-Ren also participated in the research. Professors Keke-Yi and Wenyuan-Ruan are the corresponding authors of the paper.

Paper link: https://www.nature.com/articles/s41477-023-01612-9 

Figure 1. Flowchart of the Inorganic Orthophosphate Staining Assay (IOSA).

Figure 2. Screening and cloning of novel cellular Pi distribution regulators of leaf using the IOSA method.