Genetics and biochemistry of starch accumulation modifiers in the endosperm of sugary1 maize

Understanding biosynthetic mechanisms of starch synthesis in the developing maize (Zea mays L.) endosperm has the potential to enhance uses of modified starches and identify additional genetic modifiers for increasing flavor characteristics of sweet corn. The sugary1-ref ( su1-ref ) allele of maize has been used to understand the function of starch debranching enzymes in starch biosynthesis and is the genetic basis for much of the commercial sweet corn in the United States. The primary effect of su1-ref is decreased concentration of starch in the endosperm and the accumulation of large quantities of water-soluble polysaccharides (WSP).;Pseudostarchy maize inbreds (su1-ref/su1-ref) accumulate near wild-type levels of starch in the kernels even though the su1-ref allele is present. Evaluation of polysaccharide concentrations in immature kernels determined that starch and WSP accumulates in pseudostarchy inbreds at the same level as wild type maize kernels without su1-ref. In mature kernel tissue, amylose to amylopectin ratio was similar among pseudostarchy and wild-type maize kernels indicating that the increased starch production is not due to greater levels of amylose. A complex mating design was used in two locations in 2012 and one location in 2013 to produce inbred, F1, F2, and BC1 seed of 151 genetic entries when three pseudostarchy and four extreme sugary inbreds were crossed together. The material was evaluated with a novel Near Infrared Transmittance Spectroscopy equation to measure polysaccharide concentrations. Generation means and a genetic model for triploid endosperm traits demonstrated that the primary genetic affect controlling starch accumulation in pseudostarchy inbreds is additive endosperm effects.;To determine if genetic variation of another starch debranching enzyme gene, Isa2, could be useful for modifying carbohydrate concentrations in su1-ref kernels, a population was created where the isa2-339 and su1-ref alleles were segregating. When double mutant progeny were compared to the su1-ref, isa2-339 parent it was shown that isa2-339 decreases starch and increases sugar concentration in su1-ref kernels. The isa2-339 allele is a potential source of genetic variation useful for attempting to increase flavor characteristics of sweet corn.