Arbuscular mycorrhizal fungi (AMF), the mutualistic symbionts with most
crops, constitute a research system of human-associated fungi whose
relative simplicity and synchrony are conducive to experimental ecology.
However, little is known about the shifts in adaptive strategies of
sorghum associated AMFs where strong AMF succession replaces initially
ruderal species with competitive ones and where the strongest plant
response to drought is to manage these AMF. First, we hypothesize that,
when irrigation is stopped to mimic drought, competitive AMF species
should be replaced by AMF species tolerant to drought stress. We then,
for the first time, correlate AMF abundance and host plant transcription
to test two novel hypotheses about the mechanisms behind the shift from
ruderal to competitive AMF. Surprisingly, despite imposing drought
stress, we found no stress tolerant AMF. Remarkably, we found strong and
differential correlation between the successional shift from ruderal to
competitive AMF and sorghum genes whose products (i) produce and release
strigolactone signals, (ii) perceive
mycorrhizal-lipochitinoligosaccharide (Myc-LCO) signals, (iii) provide
plant lipid and sugar to AMF and, (iv) import minerals and water
provided by AMF. These novel insights into host gene expression and
succession of AMF show adaptive strategies evolved by AMF and their
hosts and provide a rationale for selecting AMF to reduce inputs and
maximize yield in commercial agriculture. Future research opportunities
include testing the specifics and generality of our hypotheses by
employing genetically modified host plants, and exploring additional
genes underlying the adaptive strategies in natural succession.
Effects of Inoculum Additions in the Presence of a Preestablished Arbuscular Mycorrhizal Fungal Community
