Grass Rhizome Proteomics Reveals Convergent Freezing-Tolerance Strategies

Area of Science:

• Plant Science
• Molecular Biology
• Evolutionary Biology

Background:

• Elite maize lacks the cold tolerance necessary for early planting in temperate regions.
• Extending the maize growing season could enhance productivity and nutrient use efficiency.
• Wild PACMAD grasses have convergently evolved freezing tolerance in their rhizomes.

Purpose of the Study:

• To uncover the molecular basis of convergent evolution of freezing tolerance in wild PACMAD grasses.
• To identify conserved protein-level adaptations associated with winter dormancy and frost tolerance.
• To explore potential targets for improving cold tolerance in maize.

Main Methods:

• Proteomic analysis using tandem mass tag labeling and shotgun mass spectrometry on rhizome tissues.
• Comparison of protein abundance during winter dormancy and summer activity across five grass species.
• Bioinformatic analysis of protein families, functional enrichment, and structural properties.

Main Results:

• 330 protein families were consistently upregulated in winter across all five species.
• Three protein families—late embryogenesis abundant 3 (LEA3), aldose reductase, and phosphatidylethanolamine-binding protein (PEBP)—were universally upregulated.
• Conserved hydrophobicity patterns in LEA3 proteins were observed in cold-tolerant species but altered in maize.
• Functional enrichment revealed recurrent use of cryoprotectants like lipid transfer proteins and heat shock proteins.

Conclusions:

• Independent evolution of rhizome frost tolerance in PACMAD grasses is governed by similar mechanisms.
• Expression-level changes complemented by protein structural adaptations are key drivers of freezing tolerance.
• Conserved signatures in rhizome proteomic responses resemble seedling leaves, highlighting shoot-derived identity.
• Identified conserved proteins and pathways offer candidate targets for enhancing freezing tolerance in maize.