June 15, 2022
Release Subtitle:
In a recently published study, researchers from Japan identified the DOMINANT AWN INHIBITOR gene in sorghum and its underlying mechanisms
Release Summary Text:
An awn is a needle-like structure seen in grass species, whose presence
or absence in plants is controlled genetically. However, this mechanism
is poorly understood in sorghum, a cereal widely consumed around the
world. Now, researchers from Japan have identified the “DOMINANT AWN INHIBITOR” (or DAI)
gene in sorghum to be responsible for inhibiting awn elongation. Their
findings provide novel insights into common mechanisms of awn inhibition
across various cereal crops.
Full text of release:
Over the years, the domestication of grasses like wheat, rice, barley,
and sorghum for consumption has resulted in certain modifications to
their morphology. One such modification is the partial or complete
elimination of the ‘awns’, which are the bristle- or needle-like
appendages extending from the tip of the lemma in grass spikelets. The
awn protects the grains from animals, promotes seed dispersal, and helps
in photosynthesis in grasses like barley and wheat. However, its
presence also hinders manual harvesting and reduces its value as
livestock feed, explaining its elimination during domestication.
In the past, genetic studies have revealed the mechanism underlying awn
development in crops such as rice and wheat. These indicate the
possibility of the existence of complex and distinct genetic networks
controlling awn formation in a species-specific manner. In fact, the
existence of an awn-inhibiting gene in sorghum was identified in 1921,
but remained uncharacterized thereafter. Now, a group of researchers—led
by Prof. Wataru Sakamoto of Okayama University and including Prof.
Hideki Takanashi of the Graduate School of Agriculture and Life Science,
Tokyo University—has finally shed light on this subject. Their research
was published in Plant & Cell Physiology on 30 May 2022.
Justifying the rationale behind studying awn inhibition in sorghum, Prof. Sakamoto says, “Sorghum
is an important C4 crop for high biomass and bioenergy. It has a high
tolerance to drought, besides being the fifth largest cultivated cereal
crop. Also, it is a morphologically diverse crop with a relatively small
genome size, making it suitable for genetic studies in various
agronomical traits.”
For the purpose of this study, a recombinant inbred population derived
from a cross between “awnless” (BTx623) and “awned” (Takakibi NOG)
sorghum varieties was created. “The prospect of gene hunting in sorghum using the population we generated for the last ten years was motivating”,
comments Prof. Sakamoto. Using next-generation sequencing, the
researchers established a high-density genetic map of this recombinant
cultivar. Next, they performed quantitative trait loci analysis of the
sorghum germplasm to identify the gene controlling awn development. They
also conducted genome-wide association studies to identify the origins
of the awn-inhibiting gene. Lastly, they introduced the awn-inhibiting
gene in an awned rice cultivar to check its functionality in other grass
species.
The researchers observed that approximately half of the recombinant
cultivar population studied did not develop awns, just like their
awnless parent. Moreover, they found a single locus on the cultivar
chromosome to be responsible for regulating the absence as well as
shortening of awns in the cultivars studied. They identified the gene
corresponding to this locus as DOMINANT AWN INHIBITOR, or DAI.
The researchers found that DAI encodes a protein in the ALOG family, which negatively regulates awn formation as a transcription factor. Interestingly, when DAI was introduced into the awned rice cultivar, it suppressed awn formation. In the words of Prof. Sakamoto, “It
was surprising that DAI also inhibits awn elongation in rice grains,
because no such genes have been reported in rice. Thus, eliminating awns
in cereal grains have occurred differently among cereal crops, but the
mechanism can be shared between them.”
In short, this study has established the importance of DAI
for the development of modern awnless cultivars. Also, it points to the
existence of a common mechanism of awn inhibition, despite the
existence of species-specific inhibitors. Going ahead, further analysis
is needed to understand the transcriptional regulation of DAI besides
clarifying the association of DAI with sorghum domestication. As Prof.
Sakamoto points out, “In the long term, the understanding of genetic traits affecting cereals can help us in making new varieties.”
Release URL:
https://www.eurekalert.org/news-releases/955896
Reference:
DOMINANT AWN INHIBITOR Encodes the ALOG Protein Originating from Gene
Duplication and Inhibits AWN Elongation by Suppressing Cell
Proliferation and Elongation in Sorghum
Journal: Plant and Cell Physiology
DOI:10.1093/pcp/pcac057
Contact Person: Wataru Sakamoto
Prof. Wataru Sakamoto is associated with the Institute of Plant Sciences
and Resources at the Okayama University in Japan. Prof. Sakamoto holds a
PhD from the University of Tokyo. With more than 30 years of experience
to his credit, Prof. Sakamoto has developed expertise in areas like
photosynthesis, organelle genome, gene expression and chloroplast
biogenesis, to name a few. Having published more than 120 papers over
the years, he is best known for his pioneering work on leaf variegation
mutants in Arabidopsis.
https://www.okayama-u.ac.jp/eng/research_highlights/index_id162.html
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