Yeast and bacteria together biosynthesize plant hormones for weed
control
Synthetic strigolactones could also improve nutrient uptake in crops


Date:
September 18, 2021
Source:
University of California - Riverside
Summary:
Plants regulate their growth using hormones, including a group
called strigolactones that prevent excessive budding and branching.

Strigolactones also help plant roots form symbiotic relationships
with microorganisms that allow the plant to absorb nutrients from
the soil.

These two factors have led to agricultural interest in using
strigolactones to control the growth of weeds and root parasites,
as well as improving nutrient uptake. These root-extruding compounds
also stimulate germination of witchweeds and broomrapes, which
can cause entire crops of grain to fail, making thorough research
essential prior to commercial development. Now scientists have
synthesized strigolactones from microbes.



FULL STORY ========================================================================== Plants regulate their growth and development using hormones, including
a group called strigolactones that prevent excessive budding and
branching. For the first time, scientists led by UC Riverside have
synthesized strigolactones from microbes. The work is published in the open-access journal, Science Advances.


========================================================================== Strigolactones also help plant roots form symbiotic relationships
with microorganisms that allow the plant to absorb nutrients from the
soil. These two factors have led to agricultural interest in using strigolactones to control the growth of weeds and root parasites, as
well as improving nutrient uptake.

These root-extruding compounds don't come without risks. They also
stimulate germination of witchweeds and broomrapes, which can cause
entire crops of grain to fail, making thorough research essential prior
to commercial development.

Scientists are still learning about the physiological roles played by
this diverse group of hormones in plants. Until recently, manufacturing
pure strigolactones for scientific study has been difficult and too
costly for agricultural use.

"Our work provides a unique platform to investigate strigolactone
biosynthesis and evolution, and it lays the foundation for developing strigolactone microbial bioproduction processes as alternative sourcing,"
said corresponding author Yanran Li, a UC Riverside assistant professor
of chemical and environmental engineering.

Together with co-corresponding author Kang Zhou at National University Singapore, Li directed a group that inserted plant genes associated with strigolactone production into ordinary baker's yeast and nonpathogenic Escherichia colibacteria that together produced a range of strigolactones.

Producing strigolactones from yeast turned out to be very
challenging. Although engineered yeast is known to modify the
strigolactone precursor, called carlactone, it could not synthesize
carlactone with any of the specific genes used by the researchers.



========================================================================== "This project started in early 2018, yet for over 20 months there was
basically no progress. The gatekeeping enzyme DWRF27 is not functional
no matter how we try in yeast," Li said. "Kang developed a microbial
consortium technique to produce a Taxol precursor in 2015 and that
inspired this wonderful collaboration." The team turned toward E. coli,
which had already been shown capable of producing carlactone. The
carlactone it produced, however, was unstable and could not be further
modified by engineered E. coliinto any strigolactones.

Li's group managed to optimize and stabilize the carlactone precursor.

To their delight, when the yeast and bacteria were cultured together
in the same medium, the E. coliand yeast worked as a team: E. colimade carlactone, and the yeast transformed it into various final strigolactone products. The method also produced enough strigolactones to extract and
study. Using this platform, the group identified the function of multiple strigolactone biosynthetic enzymes, showing that sweet orange and grape
have the potential to synthesize orobanchol-type strigolactones.

The team also engineered microbe metabolism to boost strigolactone
production threefold to 47 micrograms per liter, enough for scientific
study. Though commercial production of strigolactones is still a long
way off, the new method for biosynthesizing them from a yeast-bacterium consortium will help scientists learn more about this important group
of plant hormones, especially the enzymes involved.

Enzymes are protein catalysts and are responsible for modification
of carlactone by yeast. Because carlactone is unstable, it cannot be
purchased from commercial sources. As a result, many plant scientists
have difficulty studying new enzymes that may work to transform carlactone
into strigolactones.

"The new yeast-bacterium co-culture provides a convenient way for
scientists to complete such works because the bacterium makes carlactone
in situ," Zhou said.

"With discovery of more enzymes and optimization of the microbial
consortium, we can manufacture strigolactones in quantity in the future."
Li and Zhou were joined in the research by Sheng Wu, Anqi Zhou, and
Alex Valenzuela of UC Riverside; and Xiaoqiang Ma at the Singapore-MIT
Alliance for Research and Technology. The paper, "Establishment of strigolactone-producing bacterium-yeast consortium," is available here.

========================================================================== Story Source: Materials provided by
University_of_California_-_Riverside. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Sheng Wu, Xiaoqiang Ma, Anqi Zhou, Alex Valenzuela, Kang Zhou,
Yanran Li.

Establishment of strigolactone-producing bacterium-yeast consortium.

Science Advances, 2021; 7 (38) DOI: 10.1126/sciadv.abh4048 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210918085833.htm

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