Molecular mechanisms underlying the action of strigolactones involved in grapevine root development by interacting with other phytohormone signaling

Strigolactones (SLs) are vital rhizosphere signals that act as phytohormones modulating plant root growth and development. After treatment for 12 days, the synthetic SLs analog GR24 significantly increased the number and density of fine root. The data indicated that different concentrations of GR24 exerted opposite effects on lateral root (LR) initiation. High concentration (10 μM) of GR24, similar to 10 μM TIS108 (a triazole-type inhibitor of SLs), acted as a positive regulator for LR initiation, whereas the treatment with a low concentration (0.1 μM) of GR24 markedly reduced LR density. In addition, root length and surface area were markedly increased by the treatment with 10 μΜ GR24, compared with those of the controls. In root samples treated with 0.1 μM GR24, 10 μM GR24, and 10 μM TIS108, 4534, 5022, and 3803 differentially expressed genes (DEGs) were identified compared to the control, respectively. The results of RNA-Seq highlighted several DEGs, such as ARF, EBF, ERF, CYCA1, and LOB, which play critical roles in hormone signaling, cell cycle, and root growth and development in grapevines. UPLC-MS analysis further demonstrated that SLs application remarkably altered the levels of endogenous hormones. In particular, indole-3-acetic acid (IAA) content in grapevine roots treated with 10 μΜ TIS108 was approximately 4.78 times higher than that in the control, whereas it was the opposite following the 0.1 μΜ or 10 μΜ GR24 treatment. Our study provides the first comprehensive description of the effect of SLs on grapevine root development caused by interacting with other phytohormone signaling, and lays a solid theoretical basis for using SLs to regulate root growth and development in grapevines.