The dual benefit of arbuscular mycorrhizal fungi under soil zinc deficiency and toxicity: linking plant physiology and gene expression
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Background and aims
Colonisation of roots by arbuscular mycorrhizal fungi (AMF) can increase plant biomass and nutrition under soil zinc (Zn) deficiency and toxicity conditions, but the genes and transporters involved in these processes are unknown. The aim here was to determine whether there is a ZIP (Zrt-, Irt-like protein) transporter gene that is differentially-regulated by mycorrhizal colonisation that may be involved in mycorrhizal Zn uptake.
We grew Medicago truncatula plants at soil Zn concentrations ranging from deficient to toxic, with and without inoculation of the AMF Rhizophagus irregularis, and measured plant dry weight, shoot nutrient concentrations and the expression of phosphate, aquaporin and ZIP genes in the roots.
At low and high soil Zn concentrations, there were positive biomass responses to AMF colonisation. Furthermore, at low soil Zn concentrations, MtZIP6 was highly up-regulated in the mycorrhizal plants. With increasing soil Zn concentration, expression of the AMF-induced phosphate transporter gene MtPT4 increased, and mycorrhizal colonisation was maintained.
We have identified two different mechanisms by which AMF colonisation can increase plant biomass under low and high Zn stress: first, up-regulation of MtZIP6 at low soil Zn to supplement Zn uptake from the rhizosphere; and second, persistence of mycorrhizal colonisation and expression of MtPT4, which at high Zn could promote increased plant biomass and reduced tissue Zn concentration.
KeywordsAquaporin Arbuscular mycorrhizal fungi Medicago truncatula Phosphate transporter Rhizophagus irregularis Zinc ZIP transporter
SJWW wishes to acknowledge support from the University of Adelaide Ramsay Fellowship. SJWW and SDT acknowledge support from the Australian Research Council Centre of Excellence in Plant Energy Biology (Grant number: CE140100008). We thank Prof. Mike McLaughlin for access to the ICP-AES, Mr. Antonio Coccina for comments on an earlier version of the manuscript, and Ms. Bogumila Tomczack, Ms. Wendy Sullivan, Ms. Rebecca Stonor and Mr. Antonio Coccina for technical assistance.
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