The Endophytic Fungus Phomopsis liquidambaris Promotes Phosphorus Uptake by Arachis hypogaea L. by Regulating Host Auxin, Gibberellins, and Cytokinins Signaling Pathways

Phosphorus (P) is an important limiting element for the growth and yield of peanut (Arachis hypogeae L.). Mutualistic fungus Phomopsis liquidambaris (B3) effectively increases host P accumulation, but the underlying mechanism is poorly understood, and this study aimed to illustrate how and the mechanism by which B3 increase P accumulation of peanut under P limitation from the perspective of phytohormone crosstalk. In this study, greenhouse pot experiments were performed to investigate the effects of B3 colonization on the phytohormone auxin (IAA), gibberellins (GAs), and cytokinins (CKs) signaling pathways of peanut under different P levels (trace P, low P, and normal P). The results revealed that B3 is capable of significantly increasing the concentrations of IAA, GAs, and CKs in peanut under low P conditions. Complementation and functional inhibition experiments demonstrated that IAA and CKs may be upstream signaling molecules of GAs and function in B3-induced expression of the AhPTH1;3 and AhPTH1;4 genes, leading to increased levels of P in peanut and consequently promoting growth. Furthermore, the improved signal transduction of phytohormones should also be important for root system architecture (RSA) establishment, which is further helpful in enhancing P absorption in peanut. Our study suggests that the endophytic fungus B3-regulated crosstalk of phytohormone signaling pathways is an important factor for increasing P accumulation in peanuts.