PHOTO: NIGEL CATTLIN/MINDEN PICTURES
SCIENCE science.orgBy G. Wilma van EsseC
ereals, such as barley and wheat, are
vital crops for both food and feed.
Modern cultivars emerge, grow, flower,
and mature uniformly, and they carry
more and bigger seeds that do not
shatter compared with their wild rela-
tives ( 1 ). Modification of plant architecture is
a key driver for further improving crop yield
but is challenging because different factors
that affect yield are often negatively cor-
related ( 2 ). On page 180 of this
issue, Zhang et al. ( 3 ) describe
the identification in common
wheat (Triticum aestivum) of
CONSTANS-like B5 (TaCOL-B5)
that affects plant architecture
by increasing both the number
of tillers [seed head (spike)–
bearing stems] and seeds per
spike, which enhances yield po-
tential by ~12%. TaCOL-B5 is a
transcriptional regulator that is
closely related to the flowering
time gene CONSTANS ( 3 , 4 ). The
discovery of TaCOL-B5 is a mile-
stone toward enhancing yield
in cereals because it improves
our understanding of molecular
mechanisms that control yield-
related architectural traits.
Agriculture is disproportion-
ally affected by climate change,
which affects plant growth
owing to changing growing
temperatures (including heat
waves), water availability, and
disease and pest pressures ( 5 ).
In combination with a rapidly
growing human population ( 6 ), there is a
need for crop varieties that produce high
yields with limited inputs of artificial fer-
tilizers and pesticides and that are resilient
to unpredictable weather. Optimizing yield
in cereals involves modulating the delicate
balance between key yield-related traits,
such as seed size, seed number, and tiller
number, as well as the timing of the transi-
tion from the vegetative to generative phase(flowering time). Variation in the gene net-
works that control these factors leads to dif-
ferent balances in plant development and
architecture ( 7 ). This offers opportunities
to use genetic variation to select or engi-
neer cereal plants that can adapt to specific
growing environments and be resilient to
changing conditions.
Yield potential in wheat and barley is
determined by flowering time, number of
tillers, number of seeds per spike, and seed
weight. The trade-off between individualcomponents, such as seed weight and num-
ber, is a major bottleneck for further yield
improvement ( 2 ). The identification of
genes that control yield-related architec-
tural traits in wheat is not trivial because
common wheat has a large (16 giga–base
pairs) and complex hexaploid genome. An
added complexity is that the wheat genome
contains >80% of repetitive DNA ( 8 )—with
so many similar genomic pieces, it is hard to
assemble the sequence jigsaw. Additionally,
transformation efficiencies are genotype de-
pendent, which limits routine genetic modi-fication to only a subset of cultivars ( 9 ). The
release of a fully annotated wheat genome
and the use of speed-breeding technology
has accelerated research in wheat ( 8 – 10 ).
Zhang et al. made shrewd use of these re-
sources to identify TaCol-B5 as a major reg-
ulator of yield.
The authors identified TaCol-B5 through
map-based cloning in a population derived
from two common wheat cultivars, Cltr17600
and Yangmai18. They found that the domi-
nant TaCol-B5 allele from Cltr17600 has a
positive yield effect. To fast-
track the functional evalua-
tion of TaCol-B5 in wheat, they
expressed the TaCol-B5 allele
from Cltr17600 in Yangmai18,
which increased tiller number
and seeds per spike under field
conditions. Notably, there was
no negative effect on seed size,
which indicates that breaking
negative correlations between
yield components is possible.
Although world cereal pro-
duction increased annually by
1.9% between 1961 and 2007,
this growth rate is projected
to reduce to a 0.9% annual in-
crease between 2007 and 2050
( 6 ). Considering this, a poten-
tial yield increase of ~12%, as
shown by Zhang et al., is a leap
forward. The TaCol-B5 allele
from Cltr17600 is not commonly
used in cultivated germ plasm.
It is therefore important to test
the effect of allelic variation in
TaCol-B5 in wheat grown in mul-
tiple environments, as well as in
other genetic backgrounds, to get a more ac-
curate assessment of the potential yield in-
creases. In addition, these results might be
translatable to other key cereal crops, such
as rice, barley, and rye.
Zhang et al. also provide a detailed analy-
sis of the mechanism by which the TaCOL-B5
transcription factor functions. They found that
a single amino acid substitution (Ser^269 Gly)
in TaCOL-B5 from Cltr1700 resulted in dif-
ferential protein phosphorylation by TAK4,
a serine-threonine protein kinase that they
identified as a key protein-protein interac-Cluster of Plant Developmental Biology, Laboratory of
Molecular Biology, Wageningen University and Research,
Wageningen, Netherlands. Email: [email protected]PLANT BIOLOGYThe quest for optimal plant architecture
Changes in plant architecture can improve cereal crop yield
PERSPECTIVES
Wheat yield is a complex trait that is determined by factors such as the number of
spike-bearing tillers per unit area, the number of seeds per spike, and seed weight.8 APRIL 2022 • VOL 376 ISSUE 6589 133