Seed-specific expression of the wheat puroindoline genes improves maize wet milling yields

The texture of maize (Zea mays L.) seeds is important to seed processing properties, and soft dent maize is preferred for both wet-milling and livestock feed applications. The puroindoline genes (Pina and Pinb) are the functional components of the wheat (Triticum aestivum L.) Hardness locus and together function to create soft grain texture in wheat. The PINs (PINA and PINB) are believed to act by binding to lipids on the surface of starch granules, preventing tight adhesion between starch granules and the surrounding protein matrix during seed maturation. Here, maize kernel structure and wet milling properties were successfully modified by the endosperm-specific expression of wheat Pins (Pina and Pinb). Pins were introduced into maize under the control of a maize gamma-Zein promoter. Three Pina/Pinb expression positive transgenic lines were evaluated over two growing seasons. Textural analysis of the maize seeds indicated that the expression of PINs decreased adhesion between starch and protein matrix and reduced maize grain hardness significantly. Reduction in pressure required to fracture kernels ranged from 15.65% to 36.86% compared with control seeds. Further, the PINs transgenic maize seeds had increased levels of extractable starch as characterized by a small scale wet milling method. Starch yield was increased by 4.86% on average without negatively impacting starch purity. The development of softer maize hybrids with higher starch extractability would be of value to maize processors.