Characterization of a Sugary1 maize (Zea mays L.) population that underwent divergent recurrent selection for endosperm starchiness

The starch accumulated in the endosperm of cereal crops is an energy source for the germinating seedling until it is photosynthetically competent, and serves as the main energy source in the diets of both humans and livestock. Consequently, understanding the genetics of starch synthesis is of great interest. The Sugary1 (Su1) locus in the maize starch pathway encodes a starch debranching enzyme which allows for the efficient packing of amylopectin into the starch granule. A lesion at this locus results in an increase in sugars and the water soluble polysaccharide phytoglycogen, at the expense of amylopectin.;Seven cycles of divergent recurrent selection for endosperm starchiness were implemented in a homozygous su1 population and revealed significant variation for several kernel and endosperm traits, including kernel weight and germination. A microarray using the RNA from individuals in the cycle six extreme sugary and cycle six pseudostarchy populations collected from 2 to 18 days after pollination (DAP) allowed unique time-course transcriptional profiles involving starch and protein synthesis to be resolved. When averaged over DAP microarray features encoding zeins were significantly up-regulated in pseudostarchy endosperm. HPLC analysis confirmed the accumulation of several zeins changed over cycles of selection, suggesting it was an indirect effect of selection.;A mapping population originating from a cross between cycle six extreme sugary and cycle six pseudostarchy was created to detect QTL associated with visual endosperm starchiness and biochemical composition. Three QTL for visual endosperm starchiness were observed in chromosome bins 6.02, 7.03, and 8.06, with QTL detected for starch, oil, and sucrose coincident with the visual endosperm starchiness QTL found in chromosome bin 6.02. Single nucleotide polymorphism (SNP) markers flanking the three QTL for visual endosperm starchiness were used to detect divergent allele frequencies of esu and psu populations in three replicate populations for QTL validation.;A diallel of three cycle six extreme sugary and four cycle six pseudostarchy inbreds was used to characterize the inheritance patterns of the pseudostarchy phenotype. Significant endosperm additive and maternal additive variance components were detected for endosperm starchiness and kernel wrinkling ratings, as well as kernel weight.