A genetically validated approach for detecting inorganic polyphosphates in plants.

Area of Science:

• Cell Biology
• Biochemistry
• Plant Science

Background:

• Inorganic polyphosphates (polyPs) are essential phosphate and energy stores found in many organisms.
• Previous methods for detecting polyPs in plants were prone to artifacts.
• The presence and role of polyPs in plants remained unclear.

Purpose of the Study:

• To develop and validate a reliable method for detecting inorganic polyphosphates (polyPs) in plant and algal cells.
• To investigate the presence and cellular localization of polyPs in various plant tissues and in algae.
• To assess the potential toxicity of polyP accumulation in plant cells.

Main Methods:

• Heterologous expression of Escherichia coli polyphosphate kinase 1 (PPK1) to induce polyP granules in Nicotiana benthamiana and Arabidopsis.
• Utilized a polyP-specific dye (JC-D7) and a polyP-binding domain (PPX1c) for detection.
• Transmission electron microscopy (TEM) to visualize polyP granules.
• Screened polyP presence in various plant organs and tissues, and in Chlamydomonas reinhardtii.

Main Results:

• Overexpression of PPK1 in plants led to growth defects, indicating cytosolic polyP accumulation is toxic.
• Successfully visualized polyP granules using JC-D7 staining and PPX1c co-localization.
• PolyP granules were not detected in higher plants.
• PolyP-rich acidocalcisomes were visualized in the green alga Chlamydomonas reinhardtii.

Conclusions:

• A robust method for polyP detection in plant and algal cells was established.
• Cytosolic polyP accumulation is detrimental to plant cell growth.
• Higher plants do not appear to store polyPs in detectable granular forms, unlike algae.