Multiple mode regulation of a cysteine proteinase gene expression in rice

In many plants, cysteine proteinases play essential roles in a variety of developmental and physiological processes. In rice (Oryza sativa), REP-1 is a primary cysteine proteinase responsible for the digestion of seed storage proteins to provide nutrients to support the growth of young seedlings. In the present study, the gene encoding REP-1 was isolated, characterized, and designated as OsEP3A. An OsEP3A-specific DNA probe was used to study the effect of various factors on the expression of OsEP3A in germinating seeds and vegetative tissues of rice. The expression of OsEP3A is hormonally regulated in germinating seeds, spatially and temporally regulated in vegetative tissues, and nitrogen-regulated in suspension-cultured cells. The OsEP3A promoter was linked to the coding sequence of the reporter gene, gusA, which encodes beta-glucuronidase (GUS), and the chimeric gene was introduced into the rice genome. The OsEP3A promoter is sufficient to confer nitrogen regulation of GUS expression in suspension-cultured cells. Histochemical studies also indicate that the OsEP3A promoter is sufficient to confer the hormonal regulation of GUS expression in germinating seeds. These studies demonstrate that in rice the REP-1 protease encoded by OsEP3A may play a role in various physiological responses and processes, and that multiple mechanisms regulate the expression of OsEP3A.