Multiple effects of the starch synthase II mutation in developing wheat endosperm

Area of Science:

• Plant Biochemistry
• Molecular Genetics
• Grain Development

Background:

• Starch synthase II (SSII), also known as SGP-1, plays a role in wheat grain development.
• A previously reported wheat line (sgp-1) lacks SSII expression.

Purpose of the Study:

• To investigate the effects of SSII deficiency on starch granule morphology and composition in wheat.
• To identify the impact of the SGP-1 mutation on other starch-modifying enzymes.

Main Methods:

• Developed doubled haploid lines from a cross between an SGP-1 mutant and a wild-type cultivar.
• Analyzed starch granule morphology and starch branching patterns at various developmental stages.
• Quantified the levels of starch branching enzymes (SBEIIa, SBEIIb) and starch synthase I (SSI) in granule-bound and soluble phases.

Main Results:

• Mutant wheat lines exhibited distorted starch granules from 15 days postanthesis.
• Increased proportion of short starch chains (DP 6-10) was observed in mutant lines, becoming pronounced at 15 days postanthesis and persisting.
• Significant reduction in granule-bound SBEII (SBEIIa and SBEIIb) and SSI was found in mutant lines.
• Soluble SBEIIb, SBEIIa, and SSI protein levels showed minimal changes.

Conclusions:

• Loss of SSII specifically leads to the depletion of granule-bound SBEIIb, SBEIIa, and SSI.
• The phenotypic effects of the SGP-1 mutation are evident from the mid-stage of wheat endosperm development.