When deficient in mineral nutrients, plant roots exude strigolactones (SLs) into the rhizosphere to encourage the symbiosis with arbuscular mycorrhizal (AM) fungi. Chemically classified as a butenolides with a four-carbon heterocyclic lactone moiety, SLs also serve as plant hormones to regulate shoot branching by inhibiting axillary bud outgrowth. Two related α/β-hydrolases encoded in plant genomes are implicated in butenolide perception: DWARF14 (D14) is the SL receptor, whereas KARRIKIN INSENSITIVE2 (KAI2) is required for response to butenolide compounds from smoke and is a likely receptor for a hypothetical butenolide ligand termed KL. The ligand(s) and function of a third α/β-hydrolase found in seed plants, D14-LIKE2 (DLK2), are unknown.
KAI2 positively regulates the expression of DLK2 and is necessary for arbuscular mycorrhizal (AM) symbiosis (1,2). Meanwhile, DLK2 negatively regulates AMF arbuscule branching and the expression of AM-responsive genes in tomato (3). Thus, we hypothesise that KAI2 is a positive regulator of AM symbiosis, whereas DLK2 limits AMF colonisation by regulating the availability of KAI2 substrates such as KL. Due to the genetic tractability and agricultural importance of barley (Hordeum vulgare), this project aims to to isolate loss-of-function mutations in DLK2 and other genes in barley via CRISPR/Cas9 mutagenesis, and to characterise their impacts on AM symbiosis and plant morphology. we also characterised the enzymatic properties and ligand preferences of two DLK2 homologues from barley. Our study will increase our knowledge about AM symbiosis, which may provide new approaches to reducing fertiliser use in agriculture.