EXPRESSION OF A SULFUR-RICH MAIZE SEED STORAGE PROTEIN, DELTA-ZEIN, IN WHITE CLOVER (TRIFOLIUM-REPENS) TO IMPROVE FORAGE QUALITY

A modified gene encoding a sulfur-rich maize seed storage protein, del ta-zein, was introduced into white clover plants by Agrobacterium-medi ated transformation. Expression of the gene was under the control of t he double 35S promoter of cauliflower mosaic virus and the nopaline sy nthase gene transcription terminator. All of the transgenic plants exp ressing transgene-specific mRNA also accumulated delta-zein in their l eaves. Levels of the HA epitope tagged delta-zein in the first fully e xpanded young leaves of different transgenic plants varied from 0.06 t o 0.3% of total water-soluble protein. Expression of the protein was a lso detected in petioles, nodes, internodes, roots and seeds of the tr ansgenic plants. N-terminal sequencing of the modified delta-zein from transgenic plants revealed that the protein is processed in white clo ver leaves as in maize seeds. All the transgenic plants expressing the delta-zein showed monogenic inheritance of the linked nptII gene conf erring kanamycin resistance. The epitope tagged delta- zein is relativ ely stable in white clover leaves and in the highest expressing plants , its accumulation increased with increasing leaf age from 0.3 (younge st leaves) to 1.3% (oldest leaves) of total water-soluble protein. The se results open up the possibility of using sulfur-rich and rumen-prot ected delta-zein to improve white clover forage quality.