The detection of endogenous 2’-deoxymugineic acid in olives (Olea europaea L.) indicates the biosynthesis of mugineic acid family phytosiderophores in non-graminaceous plants

Abstract

To acquire iron (Fe), graminaceous plants secrete mugineic acid family phytosiderophores (MAs) from their roots into the rhizosphere. MAs are biosynthesized from methionine via nicotianamine (NA). It is thought that only graminaceous plants synthesize MAs, whereas non-graminaceous plants synthesize NA which is involved in translocation of Fe within plants. In this report, using liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS), we detected 2ʹ-deoxymugineic acid (DMA), and NA in xylem sap from olive (Olea europaea L.), which is a non-graminaceous dicot plant. High-performance liquid chromatography (HPLC) confirmed the presence of these compounds in olive leaves. A transcriptome analysis of young leaves revealed several contigs encoding the putative enzymes of NA synthase, NA aminotransferase and aldo-keto reductase, which are thought to catalyze the sequential synthesis of DMA from S-adenosyl methionine. Additionally, five contigs encoding YSL (yellow stripe 1 like) transporters were identified in olive leaves. Based on these results, we propose that both NA and DMA are synthesized in olive plants and contribute to maintaining Fe homeostasis in olive trees.