Yeast and bacteria together biosynthesize plant hormones for weed control

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The hormones plants use to regulate their growth and development include strigolactones which prevent branching and excessive budding. Scientists at UC Riverside have created strigolactones using microbes for the first time. Science Advances, an open-access journal, published the work.

Strigolactones are also beneficial for plant roots, allowing them to form symbiotic relationships and absorbing nutrients from the soil. These factors have driven agricultural interest in strigolactones for controlling root parasites and root growth, as well improving nutrient uptake.

There are risks associated with root-extruding chemicals. These compounds can also be used to stimulate the germination witchweeds or broomrapes. This can lead to whole crops of grain being destroyed. Therefore, it is important to conduct thorough research before commercial development. Scientists still don't know enough about the physiological functions of this diverse set of hormones in plants. It was difficult to produce pure strigolactones in a laboratory for scientific research.

Yanran Li (UC Riverside assistant professor in chemical and environmental engineering), said that the work provided a unique platform for studying strigolactone evolution and biosynthesis, and it lays a foundation for developing strigolactone microbial production processes as an alternative source.

Li, along with Kang Zhou (co-corresponding author) at National University Singapore, directed a group that infected plant genes that are associated with strigolactone production to ordinary baker's yeast bacteria and nonpathogenic Escherichiacoli bacteria. Together they produced a variety of strigolactones.

It proved difficult to produce strigolactones using yeast. Engineered yeast can modify strigolactone precursor called carlactone but it cannot synthesize carlactone using any of the genes that were used by researchers.

"While the project was initiated in early 2018, there has been no progress for more than 20 months. Li stated that the gatekeeping enzyme DWRF27 was not functional, no matter what we do in yeast. "Kang created a microbial consortium method to produce a Taxol precursor, which inspired this amazing collaboration.

E. coli was the next option, as it had been demonstrated that it could produce carlactone. However, the carlactone it produced was unstable and couldn't be modified further by engineering E. coli to make strigolactones. The carlactone precursor was stabilized by Li's group.

Their delight was rewarded when they cultivated the yeast and bacteria together in the same medium. E.coli produced carlactone and the yeast made various strigolactone products. This method produced sufficient strigolactones for study and extraction. This platform allowed the group to identify the function of multiple strigolactone biosynthetic enzymes. It showed that sweet oranges and grapes have the potential for synthesise orobanchol-type strigolactones.

Researchers also developed microbe metabolism to increase strigolactone production by threefold to 47 micrograms per Liter. This is enough to allow for scientific research. Although commercial production of strigolactones remains a distant dream, scientists will be able to learn more about this important group, including the enzymes, using the new biosynthetic method from a yeast-bacterium consortium.

Enzymes, which are protein catalysts, are responsible for the modification of carlactone in yeast. Carlactone cannot be bought from the market because it is unstable. Many plant scientists are having difficulty finding new enzymes to convert carlactone into strigolactones.

Zhou stated that the yeast-bacterium coculture is a convenient way to finish such work because the bacteria makes carlactone in situ. We can make strigolactones in large quantities with the optimization of the microbial community and the discovery of more enzymes.

The paper is titled "Establishment of strigolactone-producing bacterium-yeast consortium."

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More information: Sheng Wu et al, Establishment of strigolactone-producing bacterium-yeast consortium, Science Advances (2021). Journal information: Science Advances Sheng Wu et al, Establishment of strigolactone-producing bacterium-yeast consortium,(2021). DOI: 10.1126/sciadv.abh4048