EXPRESSION OF A MUTANT ALPHA-ZEIN CREATES THE FLOURY2 PHENOTYPE IN TRANSGENIC MAIZE

The maize floury2 mutation results in the formation of a soft, starchy Endosperm with a reduced amount of prolamin (zein) proteins and twice the lysine content of the wild type, The mutation is semidominant and is associated with small, irregularly shaped protein bodies, elevated levels of a 7O-kDa chaperone in the endoplasmic reticulum, and a nove l 24-kDa polypeptide in the zein fraction, The 24-kDa polypeptide is a precursor of a 22-kDa alpha-zein protein that is mot properly process ed, The defect is due to an alanine-to-valine substitution at the C-te rminal position of the signal peptide, which causes the protein to be anchored to the endoplasmic reticulum, We postulated that the phenotyp e associated with the floury2 mutation is caused by the accumulation o f the 24-kDa alpha-zein protein, To test this hypothesis, we created t ransgenic maize plants that produce the mutant protein. We found that endosperm in seeds of these plants manifests the floury2 phenotype, th ereby confirming that the mutant alpha-zein is the molecular basis of this mutation.