Minimal requirements and evolution of polar membrane targeting in the land plant SOSEKI protein family

A 25-amino-acid polarity fragment in Arabidopsis thaliana SOSEKI1 (SOK1) is minimal and sufficient for stable polar targeting, with both polar and apolar faces required for membrane association.

• Why it matters: Polar protein positioning is essential for plant cell function, yet the molecular rules for polar targeting in plants remain unclear.
• What they did: The authors used extensive mutagenesis and truncation mapping to define the minimal polarity fragment, then used phylogenetics plus cross-species expression and localization to infer ancestral SOK polar pattern and its evolution.
• The result: The minimal targeting region is reconstructed as remarkably conserved across land plants, but diversifies after gene duplication, identifying a plant polar targeting peptide and mechanism for this protein family.

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