SPIRE-a software tool for bicontinuous phase recognition: application for plastid cubic membranes

Area of Science:

• Cell biology
• Nanotechnology
• Structural biology

Background:

• Bicontinuous membranes in organelles create complex nanostructures.
• Transmission electron microscopy (TEM) is crucial for analyzing these structures.
• The prolamellar body (PLB) in plant etioplasts has a key role in chloroplast biogenesis but its structure is not fully understood.

Purpose of the Study:

• To develop a tool for identifying and analyzing bicontinuous membrane structures in TEM images.
• To determine the dominant geometry of the PLB in angiosperm etioplasts.
• To gain insights into PLB structure-function relationships.

Main Methods:

• Development of the Surface Projection Image Recognition Environment (SPIRE) tool.
• Interactive identification of bicontinuous structures by comparing TEM images to mathematical models.
• Quantitative analysis of PLB geometry in etioplast TEM sections.

Main Results:

• SPIRE enabled robust identification of bicontinuous membrane structures.
• The diamond surface was identified as the dominant PLB geometry in angiosperm etioplasts, challenging previous assumptions.
• Insights into PLB membrane storage capacity and the limited role of plastid ribosome localization were provided.

Conclusions:

• The SPIRE tool is effective for analyzing complex bicontinuous membrane nanostructures.
• The diamond surface is the primary PLB geometry in angiosperm etioplasts.
• This study advances the understanding of PLB structure and its role in chloroplast biogenesis.