One of the many problems of agriculture is over-fertilization of
agricultural fields. Excess phosphorus from fertilized fields finds its way
into nearby rivers and lakes, resulting in increased aquatic plant growth.
When this happens, oxygen levels in the water plunge, leading to fish
die-offs and other harmful effects.
Researchers from Boyce Thompson Institute (BTI) have uncovered the function
of a pair of plant genes that could help improve phosphate capture and
potentially reduce the environmental harm associated with fertilization. The
discovery comes from the research of William H. Crocker Professor at BTI and
Cornell University adjunct professor Maria Harrison on plants' symbiotic
relationships with arbuscular mycorrhizal (AM) fungi.
To discover how plants control the amount of fungal colonization, the
researchers looked at genes that encode short proteins called CLE peptides
in the plants Medicago truncatula and Brachypodium distachyon. They found
two CLE genes that are key modulators of AM fungal symbiosis. One of the
genes, CLE53, reduces colonization rates once the roots have been colonized.
Another gene, CLE33, reduces colonization rates when there is plenty of
phosphate available to the plant.
The CLE peptides act through a receptor protein called SUNN, and two CLE
peptides modulate the plant's synthesis of a compound called strigolactone.
Plant roots exude strigolactone into the soil, stimulating AM fungi to grow
and colonize the root. Once the roots are colonized or there is plenty of
phosphate, the CLE genes suppress the synthesis of strigolactone, thus
reducing any further colonization by the fungi.