Scientists uncover the distribution and physiological role of planteose


Date:
January 7, 2022
Source:
Osaka Prefecture University
Summary:
The findings of this study are intended to aid botanists who
specialize in crop protection in better understanding the
distribution of planteose throughout the endosperm, perisperm,
and seed coat of Orobanche minor - - a root parasitic weed, which
is consistent with planteose's role as a storage carbohydrate. The
findings of this work demonstrate unequivocally that the enzyme
OmAGAL2, which is involved in the hydrolysis of planteose, is a
promising molecular target for root parasitic weed control.



FULL STORY ========================================================================== Witchweed (Striga spp.) and broomrapes (Orobanche and Phelipanche
spp.) are root parasitic weeds that inflict major losses in agriculture globally. Being obligate parasitic flowering plants in nature, they
parasitize other autotrophic plants of agricultural importance. The plants
are attached to their host by means of haustoria, which transfer nutrients
from the host to the parasite. Weeds reduce crop yield by competing for resources (nutrients, water and photosynthetically active radiation),
by allelopathic effects, and they reduce food, feed, and fiber quality.


========================================================================== According to a review by Chris Parker; based on rigorous sampling, there
are no reliable global figures for the total area affected by Orobanche
or Striga.

However, an estimated 16 million hectares were 'at risk' of Orobanche
attack in the Mediterranean and West Asia region. The corresponding
figure for Striga in Africa was 44 million hectares, while the total
loss of revenue from maize, pearl millet and sorghum are almost USD 2.9 billion. More recent figures suggest that 50 million hectares and 300
million farmers are affected by Striga species in Africa, with losses
amounting to USD 7 billion.

It is difficult to control parasitic weeds because they are obligate
parasites.

One potential method of control is the use of growth modulators which
are specific to root parasitic weeds. Understanding the physiological mechanisms that occur during the life cycles of root parasitic weeds is
crucial for identifying specific growth modulator targets.

Planteose (a storage carbohydrate) metabolism is a possible target
for root parasitic weed control. In a previous research Associate
Professor Atsushi Okazawa and his collaborators revealed that planteose metabolism was activated after perception of strigolactones (a class
of plant hormones that stimulate branching in plants and the growth
of symbiotic arbuscular mycorrhizal fungi) in germinating seeds of
Orobanche minor. Nojirimycin (a potent inhibitor of a- glycosidase)
inhibited planteose metabolism and impeded seed germination of Orobanche
minor, indicating that planteose metabolism is a possible target for
root parasitic weed control.

In a more recent study, this team of scientists based at Osaka Prefecture University, investigated a-galactosidases (AGALs) activities during seed germination of Orobanche minor. They also studied planteose distribution
in the dry seeds using matrix-assisted laser desorption/ionization-mass spectrometry imaging.

Planteose was found in tissues surrounding the embryo but not within it, indicating that it may have a role as a storage carbohydrate. Biochemical experiments and molecular characterization of a a-galactosidase family
member, OmAGAL2, indicated the enzyme is involved in planteose hydrolysis
in the apoplast around the embryo after the perception of strigolactones
to provide the embryo with essential hexoses for germination. These
results indicated that OmAGAL2 is a potential molecular target for root parasitic weed control.

Mass spectrometry images obtained for two fragment ions were almost
identical, indicating that these fragment ions were all generated
from a single source, planteose. The authors also provided visual aids demonstrating that planteose is distributed in the endosperm, perisperm
and seed coat in the dry seeds of Orobanche minor, which coincides with
its role as a storage carbohydrate.

In summary, the discovery of this study elucidates that (i) planteose
is distributed in Orobanche minor dry seeds and its physiological role
is elusive, (ii) during seed germination of root parasitic weeds,
planteose is rapidly hydrolyzed after perception of strigolactones
(SLs), which is indicative of its role as a storage carbohydrate (iii)
tissues surrounding the embryo, namely the endosperm, perisperm, and seed
coat, play roles in nutrient supply in root parasitic weeds. Moreover,
the novelty of this study lies in the fact that; for the first time,
the authors visualized the distribution of the storage carbohydrate
(planteose) in seeds of a root parasitic weed.

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


========================================================================== Journal Reference:
1. Atsushi Okazawa, Atsuya Baba, Hikaru Okano, Tomoya Tokunaga, Tsubasa
Nakaue, Takumi Ogawa, Shuichi Shimma, Yukihiro Sugimoto, Daisaku
Ohta.

Involvement of a-galactosidase OmAGAL2 in planteose hydrolysis
during seed germination of Orobanche minor. Journal of Experimental
Botany, 2021; DOI: 10.1093/jxb/erab527 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220107084420.htm
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