Transgene expression and agronomic improvement of rice

A reliable system for transformation and regeneration of rice protoplasts yielding fertile transgenic plants has been established. After co-electroporation of DNAs encoding a selectable marker and the gene of interest, protoplasts are regenerated to yield fertile plants. To date more than 70 different genes of interest have been successfully introduced and their patterns of expression are being studied. As in the case of dicot plants transformed by the Ti-plasm id vector approach, integration and expression appear to be stable in the transgenic monocots over several generations. Detailed com parative studies on gene expression in rice are underway using promoters for triosephosphate isomerase, a ubiquitously expressed gene encoding a cytosolic enzyme vital in the glycolytic cycle, two genes encoding members of the cyclophilin family, peptidyl-prolyl cis-trans -isomerases that are abundant in meristematic regions and are thought to participate in the correct folding of nascent proteins, and a gene encoding a tissue (root)- specific protein. Initial analyses suggest that the spatial expression of these genes in transgenic plants, using GUS reporter constructs, appears to be very sensitive to the nature of the 39 flanking region present in the gene construct. Constructs containing a coding region for arcelin, a bean seed protein with putative anti-insecticidal properties, and others containing viral sequences that may provide novel approaches for protection against tungro and other viral infections have been introduced into rice plants.