An international team of scientists found that sorghum crops planted in
areas where the parasitic plant witchweed is present were likely to have
genetically adapted to fight off the parasite.

The scientists initially wanted to find out if plants have the ability to
adapt to biotic stress factors like a parasite, much like how it can adapt
to abiotic factors like drought and salinity. Particularly, they wanted to
find out if sorghum plants found in areas where the parasitic plant called
witchweed is prevalent have evolved by having LGS1 mutations. LGS1 stands
for Low Germination Stimulant 1, and is a gene, that when mutated, affects
the crop's hormones and makes it harder for parasites to find in the soil.



They observed that LGS1 mutations were found in sorghums across Africa where
parasites were very common but were nearly absent outside of parasite-prone
regions. This led them to think that the mutations may be beneficial to the
crop. The researchers then turned to using CRISPR-Cas9 gene editing
technology to replicate the LGS1 mutations under laboratory conditions. The
loss of LGS1 function showed a relation to witchweed resistance, as the
germination rate of the parasite was found to be low or even zero. This may
suggest that the parasite was not able to find the sorghum. According to the
scientists, LGS1 mutations are known to affect strigolactone, a plant
hormone that the sorghum releases from the roots. Parasites use this hormone
to find sorghum. LGS1 mutations altering the strigolactone made the sorghum
invisible to parasites.

Further investigation is needed for this new discovery as LGS1 mutations are
also known to affect a plant's growth. The scientists noted that
strigolactones play an important role in how plants communicate with
mycorrhizal fungi, thus affects the plant's ability to acquire nutrients
from the soil. They dubbed this as a trade-off since the plant becomes
resistant to parasites but also becomes less productive. With that, the
researchers plan to study mutations in other genes that are related to
parasite-resistance such as cell-wall strengthening. They hope that their
investigations will be able to demonstrate long-term maintenance of
diversity in host resistance genes in small agroecosystems which can be used
as a comparison to both farming systems and natural communities.

[www.pnas.org]