Inoculation with arbuscular mycorrhizal fungi increase calcium uptake in Malus robusta

Utilization of plants-microbe's interactions to remediate calcium1 (Ca) deficiency soils is effective and practical. A greenhouse pot experiment was conducted to evaluate the effect of arbuscular mycorrhizal fungi2 (AMF) inoculation and the synergy of AMF and Ca fertilizer on physiological and transcriptomic responses in apple rootstock (Malus robusta) roots. AMF and Ca fertilizer synergistically served to elongate root length, surface area, average stem diameter and biomass, such extended the surface area in contact with soil nutrients and water. Symbiosis of AMF with apple seedlings made significantly higher levels of Ca in root tissue and promoted Ca translocation from roots to shoot tissue. GO and KEGG pathway analysis disclosed that gene expression varies in several critical gene families, such as auxin response (MdAux/IAAs, MdGH3 and MdSAUR), TCA cycles (MdCS, MdMDH and MdACO), phosphate transporters (MdPHT1;1, MdPHT1;10 and MdPHT1;3) and Ca2+ signal transduction pathways (MdCa2+/ATPase, MdCML, MdTPC1 and MdCDPK), indicating that apple regulates the expression of genes related to auxin synthesis, organic acid secretion, and calcium transporters and channels, thereby increased the growth of apple roots and promoted the secretion of organic acids, resulting in the increase of calcium effectiveness in soil. AMF promoted the accumulation and utilization of Ca in plants by regulating the expression levels of genes related to these pathways. These results contribute to a better understanding of AMF symbiosis mechanism behind the Ca uptake of apple seedlings under exogenous Ca treatment.