May/June 2022 - 13

LEAFY GREENS
RESEARCH
Getting rid of that gritty feeling
RESEARCHERS WORK TO CREATIVE
LESS GRITTY SPINACH VARIETIES
By Michael J. Haas
Boyce Thompson Institute
MOST OF US ARE FAMILIAR with
" spinach teeth, " the harmless but
gritty-chalky mouthfeel caused by
the vegetable.
A team of researchers from Boyce
Thompson Institute (BTI) and six
Chinese universities has identified genes
in spinach that regulate its concentration
of oxalate, which is responsible for
spinach teeth, as well as genes that
help the plant combat downy mildew,
a major disease of commercial crops.
The findings, described in a paper
published in Nature Communications
recently, could allow breeders to
produce disease-resistant varieties of
spinach with more consumer appeal.
" I think more consumers would be
willing to buy spinach that has less
oxalate, " said BTI faculty member
Zhangjun Fei, who co-led the study
and is a co-corresponding author of the
paper. " Dietary oxalate can interfere
with mineral absorption and may lead
to kidney stones, and less oxalate would
also make spinach more palatable to a
wider market. "
The research included contributors
from BTI, Cornell University, the U.S.
Department of Agriculture, Shanghai
Normal University, Zhejiang University,
Zhejiang A&F University, Qinghai
University, Qingdao Agricultural
University and Harbin Normal University.
The study compared the genomes of
cultivated spinach (Spinacia oleracea)
and two of its wild relatives (S.
turkestanica and S. tetranda) to identify
genes linked to traits of interest to plant
breeders, farmers and consumers.
" Our results provide rich resources
for the spinach community, especially
those working on increasing downy
mildew resistance, improving leaf
texture and reducing oxalate content, "
said co-corresponding author Chen
Jiao, a former postdoctoral researcher
in Fei's group who is now a professor
in the College of Agriculture and
Biotechnology at Zhejiang University.
Improving on the draft
In 2017, Fei's lab reported a draft
spinach genome, whose quality was
not high due to technical limitations
in the assembly process. The new study
used the Monoe-Viroflay cultivated
variety of spinach, which is highly
inbred, combined with the advanced
sequencing and assembly technologies,
making the assembly of its genome
much easier and of higher quality than
the varieties used in the earlier study.
The team also sequenced the
genomes of 295 cultivated varieties
of S. oleracea and 10 accessions of
the two wild relatives. Next, they
conducted comparative genomic
analyses and genome-wide association
studies (GWAS) to probe the plant's
evolutionary history and look for genes
associated with specific traits.
Most of the genetic differences
between wild and cultivated spinach
result from the plant's adaptation to
new environments as it spread from
its origins in Persia (modern-day
Iran) across Asia and Europe, with
other variations reflecting the local
preferences for traits such as flat or
wrinkled leaves.
" I think our most interesting finding
is that the genetic diversity between
Asian and European spinach is higher
than it is between cultivated and wild
spinaches, which is not very common in
other crops, " Jiao said. " This increases
our knowledge of how human selection
diversifies crop plants. "
The GWAS confirmed the known role
for the NBR-LRR family of genes in
spinach downy mildew resistance. It also
identified other locations on the genome
with lesser but still important roles in
resistance, such as a promoter region in
WSD6, which encodes an enzyme that
may reinforce the physical barrier of
spinach upon pathogen invasion.
" Like most plants, disease resistance
in spinach is controlled by a network
of genetic regions, " said Fei, who is
also an adjunct professor in Cornell's
School of Integrative Plant Science. " If
you can 'stack' disease-resistant gene
variants into one variety, then you will
get better resistance than with just one
gene variant. "
Down with oxalates
The team also found two genes
encoding metal and metal ion
transporters that may regulate oxalates
in spinach. Although more research is
needed to understand their full function,
modulating these genes to reduce
oxalates could help boost the market with
cultivars that are better for human health
and appeal to consumers who dislike
the vegetable because of spinach teeth.
However, oxalates probably play
important roles in spinach survival,
such as warding off pests and pathogens,
Fei said. If so, reducing oxalates would
also require identifying and modifying
other genes to maintain the plant's
protective mechanisms.
" Plants usually depend on networks
of genetic factors to defend themselves;
removing one means finding the right
balance among the others, " Fei said.
PRODUCE PROCESS ING
13
May/June 2022

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