How eriophyid mites shape metal metabolism in leaf galls on <i>Tilia cordata</i>

Metal metabolism in plant-galler interactions is largely unknown. We hypothesise that the mites manipulate metal distribution by sequestration of excessive levels and differential regulation of metalloproteins to support the main functions of gall-nutrition, protection and microenvironment. Using the Tilia cordata-eriophyid mites system, we aimed to reveal the role of metals in galls by investigating their distribution, speciation, gene expression and metabolome profiling. Complementary spectroscopy techniques (μXRF and μXANES tomographies, electron paramagnetic resonance), histochemical, metabolomic and transcriptomic analyses were employed. Mn was the most abundant micronutrient in the galls. Differential cell-specific Mn accumulation (idioblasts vs nutritive tissue) and speciation are essential for its homeostasis. Mn(II)-aquo complex, co-localised with Ca, sequestered in idioblasts, while Mn bound to stronger ligands including enzymes accumulated in the nutritive tissue. Zn, Cu and Fe predominately accumulated in the nutritive tissue to support intensive metabolic processes such as secondary and lipid metabolism, protein N-glycosylation and redox regulation. The slower rate of redox-sensitive spin probes' decay in the galls indicated a lower amount of antioxidants than in the leaf. We reveal essential functions of micronutrients in the galls, supporting the developmental and chemical changes in the host plant, and the nutrition of the galler.