The adaptation strategy of Astragalus mongholicus shoots to the root Fe2+ deficiency and its strong stimulating effect on glucoliquiritin apioside accumulation.

Iron is an essential micronutrient. However, nearly 40 % of arable land worldwide suffers from iron deficiency. In this study, the adaptation of shoots to root Fe2+ deficiency was investigated using hydroponically grown Astragalus mongholicus, a widely cultivated medicinal plant. The root Fe2+ deficiency significantly inhibited the plants' growth and the contents of Fe, Mo, as well as 10 metabolites, including -isorhamnetin-3-O-glucoside, and nepitrin, which have reported anti-inflammatory activities. The root Fe2+ deficiency promoted the contents of Ca, Mg, K, Zn, Mn, and 12 metabolites, among which the glucoliquiritin apioside, an anti-infection flavonoid, strikingly increased by 2480.6 times. Transcriptome analysis revealed that Fe2+ deficiency could impair cellular energy metabolism by inhibiting the expression of ATPase and other essential enzymes for the tricarboxylic acid cycle. The plants adapted to the stress by enhancing the expression of transcripts encoding V-type H+-ATPases, Ca2+ and Mg2+ transporting ATPases, Fe2+ storage protein ferritins, as well as receptor like kinase and phytohormone-related transcription factors. In the transcriptome, a transcript encoding a functional Fe2+ passive transporter was identified by complementing Fe2+/Zn2+ uptake defective yeast mutants. The adaptation strategy of Astragalus mongholicus to the Fe2+ deficiency and the potential for increasing glucoliquiritin apioside contents in the shoots by occasionally applying Fe2+ chelators to the cultivating soils were discussed.