<p>Sorghum
[<i>Sorghum bicolor</i> (L.) Moench] is a
staple food for millions of people in Africa and South Asia. It is mainly
consumed for its starch. The starch composition and structure in the seed
endosperm determines cooking properties, processing quality, and starch digestibility.
</p>
<p>An
assay to measure the alkali spreading value (ASV) of sorghum is described. The
assay was used to identify sorghum EMS mutants with variation in starch
composition. The ASV mutants (ASV+) exhibited a range of starch thermal
properties with starch gelatinization temperatures (GT) being lower or higher
than samples from Tx623 or Sepon82. The ASV+ phenotypes were found to be
correlated with starch related traits such as enthalpy (r = −0.53)
and range of starch GT (T<sub>c</sub>-T<sub>o</sub>) (r = 0.60). </p>
<p>Genes controling the ASV phenotype of sorghum and
their impact on starch quality traits are described. Whole genome re-sequencing
of sorghum EMS mutants exhibiting an ASV+ phenotype was used to identify single
nucleotide polymorphisms (SNPs) in candidate genes <i>Sobic.004G163700</i> and <i>Sobic.010G093400</i>.
The two genes were identified as a <i>SbeIIb</i>,
a putative sorghum homolog of <i>amylose
extender,</i> and as a <i>SSIIa</i>, respectively. Linkage analysis
showed that the mutations in <i>Sobic.010G093400</i>
and <i>Sobic.004G163700</i> co-segregated
with the ASV phenotype. The <i>ssIIa</i>-mutants
exhibited normal amylose values, lower starch GT and lower final viscosity than
the wild type. The <i>sbeIIb</i>-mutants
exhibited higher amylose content, higher starch GT and lower peak and final viscosity
with poor gel consistency compared to the
wild type and <i>ssIIa</i>-mutants. An
allele dosage test indicated that the <i>sbeIIb</i>-mutants
had an allele dosage dependent effect on
amylose content. Double mutants of <i>sbeIIb</i>
and <i>ssIIa</i> showed that amylose
content, starch thermal properties and paste viscosity profiles resemble the <i>sbeIIb</i> parent. </p>
<p>A study of ASV phenotypes in a panel of more than 750 sorghum
conversion lines revealed genetic variation for the ASV phenotype. A few
SC-lines exhibiting stable expression of the ASV+ phenotype over two growing
seasons. Most of these lines were described as belonging to the working group Nandyal,
durra types from India described as producing ‘glutinous grains’. Whole genome
resequencing discovered common SNPs in genes associated with starch
biosynthesis. A genome wide association study (GWAS) identified a significant SNP
that
could be associated with the starch biosynthesis gene <i>Sobic.010G273800</i>, and with candidate genes <i>Sobic.010G274800</i> and <i>Sobic.010G275001</i>
both annotated as glucosyltransferases. Grain samples from SC489, SC491, SC587
and SC589 exhibited a consistent ASV+ phenotype with lower or similar starch
GT, similar amylose content, and similar high viscosity and gel consistency compared
to controls.</p>
<p> </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8038949 |
| Date | 14 May 2019 |
| Creators | Stefanie Griebel (6632264) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/IDENTIFICATION_AND_CHARACTERIZATION_OF_GENES_CONTROLLING_THE_ALKALI_SPREADING_PHENOTYPE_IN_SORGHUM_AND_THEIR_IMPACT_ON_STARCH_QUALITY/8038949 |
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