AI Article Synopsis

  • Karrikins (KARs) are smoke-derived chemicals that enhance the germination of many plants, with specific attention to lettuce which is responsive to karrikinolide (KAR1) but less so to other forms.
  • The study revealed that lettuce has two KARRIKIN INSENSITIVE2 (KAI2) genes, with LsKAI2b showing higher expression and conferring sensitivity to KAR1, implying it is the primary receptor for this response in lettuce.
  • Analysis of KAI2 proteins across different species indicated key residues (96, 124, 139, and 161) influence ligand specificity, suggesting that fine-tuning at these locations via mutations contributes to the varied responses to KARs observed

Article Abstract

Karrikins (KARs) are chemicals in smoke that can enhance germination of many plants. Lettuce (Lactuca sativa) cv. Grand Rapids germinates in response to nanomolar karrikinolide (KAR1). Lettuce is much less responsive to KAR2 or a mixture of synthetic strigolactone analogs, rac-GR24. We investigated the molecular basis of selective and sensitive KAR1 perception in lettuce. The lettuce genome contains two copies of KARRIKIN INSENSITIVE2 (KAI2), which in Arabidopsis (Arabidopsis thaliana) encodes a receptor that is required for KAR responses. LsKAI2b is more highly expressed than LsKAI2a in dry achenes and during early stages of imbibition. Through cross-species complementation assays in Arabidopsis, we found that an LsKAI2b transgene confers robust responses to KAR1, but LsKAI2a does not. Therefore, LsKAI2b likely mediates KAR1 responses in lettuce. We compared homology models of KAI2 proteins from lettuce and a fire-follower, whispering bells (Emmenanthe penduliflora). This identified pocket residues 96, 124, 139, and 161 as candidates that influence the ligand specificity of KAI2. Further support for the importance of these residues was found through a broader comparison of pocket residues among 281 KAI2 proteins from 184 asterid species. Almost all KAI2 proteins had either Tyr or Phe identity at position 124. Genes encoding Y124-type KAI2 are more broadly distributed in asterids than in F124-type KAI2. Substitutions at residues 96, 124, 139, and 161 in Arabidopsis KAI2 produced a broad array of responses to KAR1, KAR2, and rac-GR24. This suggests that the diverse ligand preferences observed among KAI2 proteins in plants could have evolved through relatively few mutations.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9516758PMC
http://dx.doi.org/10.1093/plphys/kiac328DOI Listing

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