|The pink flowers in this field are Striga. (Image: Nagoya University)|
A molecular approach, a fluorescence turn-on probe called Yoshimulactone Green (YLG), has been used to identify the protein responsible for germination of Striga seeds.1Striga, a parasitic plant known as witchweed, has seriously affected millions of hectares of crop fields (in particular, rice and corn) in sub-Saharan Africa, infesting the host crop plant through its roots by depriving them of their nutrients and water.
Striga poses a major threat to food security; nevertheless, the exact mechanism on how Striga seeds detect host crops had not been fully clear up to now. In the study, scientists at Nagoya University (Nagoya, Japan) and the University of Toronto (Toronto, ON, Canada) developed a new fluorescent visualizing molecule to examine the process of Striga germination. The outcome of this study is expected to accelerate research to control Striga growth and to prevent crop losses of billions of U.S. dollars every year.
Striga detects host crop plants from a class of plant hormones called strigolactones released by plants. Strigolactones are known to be responsible for controlling shoot branching and to attract mycorrhizal fungi present in the soil, which supplies the plant with nutrients. Plants increase strigolactone synthesis when they are in a malnutrition state to restrain their growth and gain nutrients from fungi. However, strigolactones also trigger Striga germination, which actually leads to further deprivation of nutrients from infestation instead of escaping malnutrition.
YLG shows how Striga seeds are activated
The new turn-on probe generates green fluorescence upon reacting with and being decomposed by protein receptors detecting strigolactones in Striga, says Shinya Hagihara, one of the researchers. The probe was used in live-imaging experiments, showing that a wavelike propagation of strigolactone perception wakes up Striga seeds.
The main reason that the Striga problem has been so difficult to overcome arises from Striga's unique survival strategy. Striga seeds are small in size (about 0.3 mm) and are easily scattered by the wind. In addition, Striga seeds remain dormant in the soil for decades until it finds a host plant. Upon sensing the host plant in close proximity, the parasitic seeds germinate and infest the host plant. After absorbing the nutrients and water from the host plant, the Striga plant flowers and generates more seeds. This snowball effect makes it extremely difficult to exterminate Striga once a crop field is affected by it, and may lead to total crop failure in severe cases.
A research team at the Institute of Transformative Bio-Molecules (ITbM) at Nagoya University is currently working on developing new molecules to control Striga germination and prevent parasitism towards crop plants.
1. Yuichiro Tsuchiya et al., Science (2015); doi: 10.1126/science.aab3831