Shedding Light On A Sneaky Soil Parasite

An interdisciplinary team of researchers has developed a fluorescent molecule that can visualize germination of the parasitic plant, witchweed.

AsianScientist (Aug. 25, 2015) – Researchers have developed a fluorescent molecule that glows green in the presence of germinating witchweed (Striga hermonthica). Their findings, published in Science, could lead to better control over the parasitic plant which can cause complete crop failure.

Striga is a major threat for food crops, such as rice and corn. Striga infests the host crop plant through its roots, depriving them of nutrients and water. The host plant eventually withers, leading to yield losses in approximately 40 million hectares of land, worth over US$10 billion.

The main reason for why the Striga problem has been so difficult to overcome arises from its 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.

Striga is known to detect host crop plants by a class of plant hormones called strigolactones. Strigolactones are known to control shoot branching and attract mycorrhizal fungi that supply the plant with nutrients. When malnourished, plants increase strigolactone synthesis to restrain their growth and gain nutrients from fungi. However, strigolactones also trigger Striga germination, leading to further deprivation of nutrients.

“I figured that there must be a protein receptor in Striga that can detect minute amounts of strigolactone produced by the host plant,” says Dr. Yuichiro Tsuchiya, a plant biologist at the Institute of Transformative Bio-Molecules (ITbM) at Nagoya University.

“I was screening commercially available strigolactone derivatives with hope to find molecules that can identify the strigolactone receptor responsible for germination in Striga.”

Tsuchiya joined Nagoya University in 2013 and coincidentally came across graduate student Masahiko Yoshimura, a synthetic chemist, in a communal analytical laboratory. Upon passing each other several times, Tsuchiya started to talk about his research with Yoshimura, who quickly expressed an interest in Tsuchiya’s research. Together with Shinya Hagihara, an associate professor at ITbM who is also a chemist, Yoshimura designed a strigolactone-like molecule, which he synthesized in two days.

“I was really surprised how quickly Yoshimura-kun synthesized the probe molecule,” said Tsuchiya. “We named the molecule ‘Yoshimulactone (YLG)’, which is designed to generate green fluorescence upon reacting and being decomposed by protein receptors detecting strigolactones in Striga.”

Yoshimura first treated a model Arabidopsis plant with Yoshimulactone and found that it controls shoot branching in the same way as strigolactones does, indicating that it exhibits a similar bioactivity. When Striga seeds were treated with Yoshimulactone, the team observed seed germination along with green fluorescence.

“Our investigations show that Striga seeds possess strigolactone protein receptors,” say Tsuchiya and Hagihara. “We were also able to identify the actual proteins responsible for seed germination in Striga with the observation of green fluorescence, which appeared upon treatment with Yoshimulactone.”

Further analysis revealed that Striga‘s parasitizing mechanism is likely to work by initial recognition of a nearby host plant by detection of strigolactones and their derivatives. This point of recognition eventually becomes the root tip of Striga and triggers the awakening of the entire Striga seed, which then stimulates root growth towards the host plant.

Striga is known to wither and die if they are unable to find a host after germination. Therefore, molecules that can artificially induce Striga germination would be a promising agrochemical to control Striga germination and thus prevent parasitism towards crops.

ITbM’s research team is currently working on developing new molecules to control Striga germination and prevent parasitism towards crop plants.

The article can be found at: Tsuchiya et al. (2015) Probing Strigolactone Receptors in Striga hermonthica with Fluorescence.


Source: ITbM.
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