COORDINATED REGULATION OF THE GENES PARTICIPATING IN STARCH BIOSYNTHESIS BY THE RICE FLOURY-2 LOCUS

The recessive floury-2 (flo-2) locus of rice (Oryza sativa L.), which is located on chromosome 4, causes a strong reduction in expression of the gene encoding an isoform of branching enzyme RBE1 in immature see ds 10 d after flowering. Mapping of the RBE1 gene demonstrated the loc alization on rice chromosome 6, suggesting that the wild-type Floury-2 (Flo-2) gene regulates RBE1 gene expression in trans. However, reduce d expression of the genes encoding some other starch-synthesizing enzy mes, including another isoform of branching enzyme RBE3 and granule-bo und starch synthase, was also found in the flo-2 seeds. In spite of th e low level of RBE1 gene expression in the immature seeds of the flo-2 mutants, the RBE1 gene was equally expressed in the leaves of the wil d type and flo-2 mutants. Thus, these results imply that the Flo-2 gen e may co-regulate expression of some of the genes participating in sta rch synthesis possibly in a developing seed-specific manner.