Selection for Visual Starchiness In the Endosperm of a su1 Population Alters Zein Protein Accumulation.

The Sugary1 (Su1) locus encodes for a starch debranching enzyme with isoamylase-type activity.  The homozygous recessive state (su1/su1) results in the accumulation of phytoglycogen at the expense of starch.  Divergent recurrent selection for visual endosperm appearance was implemented in a population that was homozygous su1.  Six cycles of selection for extreme sugary (esu) and extreme starchy (pseudostarchy) (psu) endosperm were performed.  Zein profiles of the base population (cycle 0), and cycles 1-7 of selection for both the esu and psu traits were conducted.  In order to determine whether differences in zein content accompanied visual endosperm selection for endosperm appearance, HPLC analysis was used to detect zein protein absorbance over elution time.  Known peaks were identified for each trace, and the total area under the curve for peaks was calculated.  Selection cycle was significantly different when compared within each of the 18 identified peaks common across all traces.  The peak corresponding to 15 kD beta zein reveals divergent action with an overall decrease in protein accumulation over cycles of esu selection, and an overall increase over cycles of psu selection.  The behavior of the zein proteins in response to endosperm modification in this population reveals remarkable similarity to other well characterized endosperm protein modification genes including Opaque2 and Floury2 which also alter endosperm appearance.