Page 178 - PC2019 Program & Proceedings

PLANT CANADA 2019

S141. Increasing soybean oil yield through targeted gene silencing and overexpression
Fedosejevs, E.; Y. Ye; E. Myers; J. Thelen
University of Missouri

Soybean oil content is lower than most oilseed crops at 16-22% of dry weight. We are developing
soybean germplasm with improved oil content and seed yield through rational metabolic engineering. To
do this, we are primarily targeting the enzyme acetyl-CoA carboxylase (ACCase), which catalyzes the
entry point into fatty acid biosynthesis, carboxylating acetyl-CoA to malonyl-CoA. Increasing ACCase
activity provides a “push” of fatty acids into FA biosynthesis, resulting in increased oil production. We
have developed and are testing soybean lines 1) that incorporate a gene silencing cassette that reduces
expression of a family of negative regulators of fatty acid biosynthesis called biotin/lipoyl attachment
domain containing-proteins (BADCs) or 2) that overexpress a modified form of the limiting subunit of
heteromeric ACCase, α-carboxyltransferase (α-CT). These strategies have demonstrably increased oil
content in the model organisms Arabidopsis thaliana and Camelina sativa. We are also pursuing further
strategies to improve soybean seed yield and oil content, including by repressing α-CT interactor protein
(CTI), a new ACCase interactor that our lab recently discovered (Ye et al., unpublished), and by boosting
seed sink strength through overexpression of an engineered form of sucrose synthase (SUS). Additional
novel regulators of FA biosynthesis are being identified through traditional biochemical techniques and
via co-expression meta-analyses of massive RNA-seq data sets with a software tool that we are
developing (RNA-see).

Eric Fedosejevs (fedosejevse@missouri.edu)

S142. A compensatory mutation in the GmNFR5α gene restores soybean-rhizobia symbiosis fitness
Torkamaneh, D.; F. Chalifour; C. Beauchamp; H. Maaroufi; F. Belzile
Université Laval

In soybean, NFR5α is a key regulator of root-hair curling in response to Nod factors (NFs) released by
rhizobacteria and plays an essential role in the initiation of symbiosis. Sequencing of the entire
transcribed region of NFR5α in 297 African soybean lines revealed two non-synonymous (E345K and
M490V) mutations defining three alleles. Each of these exhibited a distinct phenotype, with one mutation
(E345K) causing a severe decrease (35%) in symbiotic-nitrogen fixation (SNF) activity while the second
mutation (M490V) partially compensated (60% restoration) for this decrease. As all three alleles are
expressed equally (in terms of mRNA abundance), we hypothesized that the uncovered mutations have a
structural impact on protein function. We found that the substitution E345K introduces a positively
charged amino acid residue that would be expected to cause a repulsion between the NFR5α and ROP6
proteins, this interaction being essential for root-hair curling. The predicted NFR5α-ROP6 binding
affinity was decreased in the E345K mutant allele while, in the double mutant (E345K + M490V), the
predicted binding affinity was increased, a form of epistasis. However, although all three alleles were
frequently present in wild soybeans (G. soja), we found evidence of purifying selection, during soybean
domestication, against the unfavorable allele (E345K) in cultivated soybeans (G. max). This study
provides fundamental insights into NFR5α and its essential role in the initiation of SNF in soybean.

Davoud Torkamaneh (davoud.torkamaneh.1@ulaval.ca)

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