Sl‐IAA27 regulates strigolactone biosynthesis and mycorrhization in tomato (var. MicroTom )

Summary Root colonization by arbuscular mycorrhizal ( AM ) fungi is a complex and finely tuned process. Previous studies have shown that, among other plant hormones, auxin plays a role in this process but the specific involvement of Aux/ IAA s, the key regulators of auxin responses, is still unknown. In this study, we addressed the role of the tomato Sl‐IAA27 during AM symbiosis by using Sl‐IAA27‐RNAi and pSL‐IAA27 :: GUS stable tomato lines. The data show that Sl‐IAA27 expression is up‐regulated by the AM fungus and that silencing of Sl‐IAA27 has a negative impact on AM colonization. Sl‐IAA27 ‐silencing resulted in down‐regulation of three genes involved in strigolactone synthesis, NSP1, D27 and MAX1 , and treatment of Sl‐IAA27 ‐silenced plants with the strigolactone analog GR24 complemented their mycorrhizal defect phenotype. Overall, the study identified an Aux/ IAA gene as a new component of the signaling pathway controlling AM fungal colonization in tomato. This gene is proposed to control strigolactone biosynthesis via the regulation of NSP1 .