Modification of plant height via RNAi suppression of OsGA20ox2 gene in rice

GA 20-oxidase (GA20ox) is a regulatory enzyme for the syntheses of biologically active GAs in plants. The loss-of-function mutations in OsGA20ox2 of rice (Oryza sativa L.) generate the well-known Green Revolution gene sd-1, which cause the semi-dwarfism phenotype. In our present investigation, semi-dwarf plants were generated from a taller rice variety QX1 by RNAi suppression on the expression of OsGA20ox2. The 531bp-fragment of OsGA20ox2 was amplified by PCR from genomic DNA of QX1 and used to construct the hairpin RNAi vector pCQK2. The wild type QX1 was transformed with pCQK2 by Agrobacterium-mediated transformation and some independent transgenic RNAi lines exhibited semi-dwarfism. RT-PCR and Northern blot analyses showed that the expression of OsGA20ox2 was specifically suppressed in the RNAi semi-dwarf lines. Endogenous GA assays revealed that the contents of the GA20ox2-catalyzed products GA19, GA20 and the down-stream biologically active GA1 were drastically reduced in the RNAi semi-dwarf lines. We further showed that the RNAi semi-dwarf lines could be restored to normal plant height by applying exogenous GA3. The results indicated that the semi-dwarfism of the RNAi semi-dwarf lines was associated with the decreased expression of OsGA20ox2 gene and the reduced content of endogenous biologically active GA1. Analyses of panicle length, seeds per panicle and 1000-grain weight suggested that the RNAi semi-dwarf lines showed stable grain yield compared with the wild type plants. It is demonstrated that the RNAi approach could be useful for plant breeding purposes in the future.