Fig 9. L. japonicus KAI2a and KAI2b display organ-specific redundancy and differ in their ligand-binding specificity.

(A) LjKAI2a is required to mediate inhibition of hypocotyl growth in response to KAR₁ and KAR₂. In roots LjKAI2a and LjKAI2b redundantly promote postembryonic root density, but only in response to KAR₁ treatment. (B) In the Arabidopsis kai2-2 background LjKAI2a mediates hypocotyl growth inhibition in response to KAR₁, KAR₂ and GR24^ent-5DS. In the same background, LjKAI2b mediates a stronger response to KAR₁ than to KAR₂ and no response to GR24^ent-5DS (indicated by a red cross). Three divergent amino acids at the binding pocket are indicated in white. (C) Swapping the three divergent amino acids in the binding pocket reconstitutes GR24^ent-5DS activity through LjKAI2b and abolishes GR24^ent-5DS activity through LjKAI2a. Among the three amino acids F157/W158 are decisive for GR24^ent-5DS binding (strong colors), while L160/M161 and S190/L191 play a weaker role (pale colors). Amino acids from LjKAI2a have a red/pale red and amino acids from LjKAI2b a violet/pale background.