Transgenic rice: A valuable monocot system for crop improvement and gene research

Since the first fertile transgenic rice was obtained during the late 1980s, studies on rice transformation have undergone rapid strides. Several physi cal methods of gene delivery, including Agrobacterium, have been employed t o produce transgenic rice. Up to now, about 50 rice cultivars have been tra nsformed that include many japonica and also a few indica cultivars. Conseq uent to the availability of an efficient transformation system in rice, the expression of monocot genes is better understood because expression of sev eral genes and regulatory elements from rice and other related cereals such as wheat has been studied in rice. Genes of agronomic importance for herbi cide, insect, virus, and fungal resistance have been introduced in rice, an d some of the transgenics have already completed a few years of field trial s. In this context, rice is being looked on as a model monocot plant to stu dy gene expression and to introduce agronomically useful genes. While this progress is expected to supplement conventional breeding program of rice im provement in the near future, some impediments in the successful implementa tion of transgene technology, such as gene silencing, the presence of undes irable selection/marker genes, high cost, and constitutive vs. targeted/opt imal expression of genes, are addressed.