Gibberellin biosynthesis in Lotus japonicus regulates arbuscule distribution, but not overall colonisation by arbuscular mycorrhizal fungi

Gibberellins have been reported to play both positive and negative roles in arbuscular mycorrhizal (AM) symbioses. Despite extensive characterisation of the role of DELLAs in AM colonisation, studies of gibberellin function have largely been restricted to chemical interventions. Few studies have examined how disruption to gibberellin biosynthesis affects AM symbioses. To explore this further, we obtained Lotus japonicus LORE1 transposon insertion mutants in four key gibberellin biosynthetic genes: CPS, KS, KO , and KAO . Through a characterisation of their developmental phenotypes, we determined that for each gene there is a single homolog which has a major role in gibberellin biosynthesis. We name these genes CPS1, KS1, KO1 , and KAO1. Mutations in these genes affect AM colonisation in the overall distribution of arbuscules, but not in total colonisation levels. These results are consistent with previous studies indicating that DELLAs control the number of cortical cell layers, and therefore regulate the number of cells able to accommodate arbuscules.