EXPRESSION OF THE PEA ALBUMIN-1 GENE IN TRANSGENIC WHITE CLOVER AND TOBACCO

In order to improve the quality of pasture protein for ruminant animal nutrition, we are introducing genes encoding rumen-protected proteins , rich in essential amino acids, into white clover (Trifolium repens L .). We have introduced a chimaeric gene transcribed from the 358 CaMV promoter, and encoding the pea albumin 1 (PA1) protein, rich in sulphu r amino acids, into the white clover genotype WR8 by Agrobacterium-med iated transformation. A transgenic plant with high levels of PA1 mRNA was crossed with a commercial genotype from cv. Regal Ladino and both the parent and progeny plants were analyzed for expression and accumul ation of PAI gene products. Steady-state mRNA levels and transcript si zes in transgenic parent and progeny were comparable. The abundance an d stability of the PA1 protein in transgenic white clover plants was e xamined by immunoselection of in vivo [S-35]Na2SO4-labelled plant prot eins. Evidence is presented here, that the 11 kDa PA1 proprotein precu rsor is processed correctly in petiole tissues of newly regenerated wh ite clover plantlets but only the 6 kDa PA1a subunit accumulates in le aflets of tissue-culture-grown and older glasshouse-grown clover plant s. Attempts to enhance PA1 abundance by altering its subcellular targe t in transgenic tobacco plants suggest that the endomembrane system is a relatively stable environment compared with the cytoplasm or chloro plast, for the accumulation of PA1, despite its low abundance there (< 0.001% total cell protein).