Constitutive expression of the defense-related Rir1b gene in transgenic rice plants confers enhanced resistance to the rice blast fungus Magnaporthe grisea

The Rir1b gene of rice (Oryza sativa) is one of a set of putative defense g enes whose transcripts accumulate upon inoculation of rice with the non-hos t pathogen Pseudomonas syringae pv. syringae. It belongs to a family of gen es encoding small extracellular proteins so far only identified in cereals. To assess the function of the Rir1b gene in rice blast resistance, it was placed under the control of the CaMV 35S promoter and transferred into rice plants of the japonica variety Taipei 309 by biolistic transformation of i mmature embryos. Two out of 12 hygromycin-resistant regenerated plants (OE1 and OE3) were fertile. DNA gel blot analysis suggested that these two T-0 plants were independent transformants, each of which had stably incorporate d one complete copy of the transgene into the genome. In addition, the OE1 plant appeared also a contain a rearranged copy or incomplete copy. T-1 pla nts homozygous for the transgene were identified by DNA gel blot analysis o f individual T-2 progeny and further propagated. Expression analysis of the transgene showed that the transgene was active both in T-1 plants and homo zygous decendants. Challenge inoculation of homozygous transgenic plants wi th Magnaporthe grisea, the causal agent of rice blast disease, revealed tha t both independent transgenic lines were more resistant than the untransfor med wild type, suggesting that over-expression of the Rir1b gene confers pa rtial resistance against this important pathogen.