The C24-methyl/ethyl sterol ratio is increased by Rhizophagus irregularis colonization

Area of Science:

• Plant biology
• Mycology
• Biochemistry

Background:

• Plant-microorganism interactions are crucial for ecosystem functions, notably plant nutrition via mutualisms like arbuscular mycorrhizal (AM) symbiosis.
• Lipids, especially sterols, are implicated in AM symbiosis signaling, but their precise roles remain unclear.

Purpose of the Study:

• To investigate the impact of AM symbiosis on root sterol content and composition across eleven diverse plant species.
• To analyze the differential expression of genes involved in sterol biosynthesis (SMT1 and SMT2) in response to AM fungal colonization.

Main Methods:

• Sterol content and composition were analyzed in roots of eleven model plants (banana, barrelclover, flax, grapevine, maize, pea, poplar, potato, rice, sorghum, tomato) with and without colonization by Rhizophagus irregularis.
• Transcript levels of SMT1 and SMT2 genes were quantified in colonized versus non-colonized roots.
• Phylogenetic analysis of SMT1 and SMT2 gene families was performed across a wide range of plant and fungal genomes.

Main Results:

• A consistent increase in C24-methyl sterols was observed in colonized roots compared to non-colonized roots across all studied plants.
• SMT1 and SMT2 gene transcripts showed differential accumulation in colonized roots, but without a common regulatory pattern among species.
• Phylogenetic analysis identified distinct clades for SMT1 and SMT2 family members.

Conclusions:

• Arbuscular mycorrhizal symbiosis induces a conserved regulation of root sterol composition in angiosperms, specifically elevating C24-methyl sterols.
• Plant-specific variations in gene regulation highlight the nuanced nature of this symbiotic interaction.
• Sterols likely play a significant, conserved role in the signaling pathways of arbuscular mycorrhizal symbiosis.