Expression of natural antimicrobial human lysozyme in rice grains

In the present study, we explored the expression of human lysozyme in maturing rice grains. Particle bombardment-mediated transformation was utilized to deliver the codon-optimized structural gene for human lysozyme to the callus of rice cultivar Taipei 309. Lysozyme expression is controlled by the promoter and signal peptide sequence for rice storage protein Glutelin 1. A total of 33 fertile plants were regenerated from independent transformation events and 12 of them with significant expression levels of lysozyme were advanced to further generations. The transgenes were characterized by PCR and Southern blot analysis. Segregation analysis indicated a typical Mendelian 3: 1 inheritance, suggesting a single locus or closely linked loci of gene insertion. The expression levels of lysozyme reached 0.6% of the brown rice weight or 45% of soluble proteins. Seven transgenic breeding lines have been selected and followed over six generations. Lysozyme expression levels were maintained in all generations. Biochemical, biophysical and functional comparisons of native and recombinant human lysozyme revealed identical N-terminal sequence, molecular weight, pI and specific activity. Similar thermal and pH stability was observed for lysozyme from two sources. Furthermore, similar bactericidal activity was displayed towards a laboratory strain of E. coli. The possibility of improving medical and nutritional quality of infant formulas and baby foods with rice flour or rice extract containing recombinant human lysozyme is discussed.