Two AMP-Binding Domain Proteins from Rhizophagus irregularis Involved in Import of Exogenous Fatty Acids.

Arbuscular mycorrhizal fungi (AMF) colonize roots, where they provide nutrients in exchange for sugars and lipids. Because AMF lack genes for cytosolic fatty acid de novo synthase (FAS), they depend on host-derived fatty acids. AMF colonization is accompanied by expression of specific lipid genes and synthesis of sn -2 monoacylglycerols (MAGs). It is unknown how host-derived fatty acids are taken up by AMF. We describe the characterization of two AMP-binding domain protein genes from Rhizophagus irregularis , RiFAT1 and RiFAT2 , with sequence similarity to Saccharomyces cerevisiae fatty acid transporter 1 ( FAT1 ). Uptake of 13 C-myristic acid (14:0) and, to a lesser extent, 13 C-palmitic acid (16:0) was enhanced after expression of RiFAT1 or RiFAT2 in S. cerevisiae Δ fat1 cells. The uptake of 2 H-labeled fatty acids from 2 H-myristoylglycerol or 2 H-palmitoylglycerol was also increased after RiFAT1 and RiFAT2 expression in Δ fat , but intact 2 H-MAGs were not detected. RiFAT1 and RiFAT2 expression was induced in colonized roots compared with extraradical mycelium. 13 C-label in the AMF-specific palmitvaccenic acid (16:1Δ11) and eicosatrienoic acid (20:3) were detected in colonized roots only when 13 C 2 -acetate was supplemented but not 13 C-fatty acids, demonstrating that de novo synthesized, host-derived fatty acids are rapidly taken up by R. irregularis from the roots. The results show that RiFAT1 and RiFAT2 are involved in the uptake of myristic acid (14:0) and palmitic acid (16:0), while fatty acids from MAGs are only taken up after hydrolysis. Therefore, the two proteins might be involved in fatty acid import into the fungal arbuscules in colonized roots.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.