Engineering Resistance To Rice Blast Disease By Transgenic Approach

Rice blast is one of the most serious diseases in rice. Rice blast, bacterial leaf blight and rice sheath blight are listed as the three main diseases in rice. Currently, many rice blast resistance genes have been cloned and characterized most of which belong to NBS-LRR family. Moreover, a part of these genes are multiple alleles and they confer race-specific resistance with narrow spectrums. Because of the fast variation of dominant races in nature, it is easy for blast fungus to escape from the recognition of resistance genes. Thus, the application of cloned resistance genes is limited. Therefore, looking for broad-spectrum and durable resistance resources and utilization of heterologous resistance genes are important research directions of exploring new strategies for the disease control. In the present study, we tested ectopic expression of RPW8.1 and RPW8.2, siRNA that targeting MoAPl, miR160a and miR398b in rice to engineer resistance against blast disease in rice and obtained the corresponding transgenic rice lines as described below.RPW8 locus is obtained from the Arabidopsis MS-0 through map-based cloning. It contains two closely linked genes, RPW8.1 and RPW8.2, both confer broad-spectrum resistance to powdery mildew. Upon powdery mildew infection in Arabidopsis, RPW8.2 is specifically targeted to and integrated in the extra-haustorial membrane (EHM). On the contrast, how RPW8.1 activates resistance against powdery mildew is largely unclear, although transgenic Arabidopsis liens are resistant to powdery mildew. To test whether heterologous resistance genes can initiate resistance, we introduced the construct expressing RPW8.1 and RPW8.2 into rice. Our data demonstrate that transgenic line expressing RPW8.1 and RPW8.2 were resistance to rice blast. The expression of defense-related genes PR10 and PBZ1 were highly induced. By Laser Scanning confocal microscopy, we found that a lot of appressoria were formed at 12 hours, then a large number of invasive hyphae were generated in the control lines. By the contrast, the formation of appressoria and invasive hyphae were reduced and delayed in the transgenic lines expressing RPW8.1. Thus, it is possible to engineer resistance by ectopic expression of RPW8.1 and RPW8.2 in rice.miRNA is indispensable in regulating plant growth and defense.We identified some miRNAs that were up-regulated upon blast fungal infection.We obtained transgenic lines over-expressing two miRNAs,miR160a and miR398b,and found that the transgenic plants expressing these two miRNAs were resistance to the blast disease.RNA interference is a technique widely used in functional analysis of interested genes. During blast.fungal infection rice plant,a transcription factor,MoAP1,plays an indispensable role for pathogenesis.We designed small interfering RNA(siRNA)targeting MoAP1 and introduced into rice through Agrobacterium-mediated transformation.The transgenic plants expressing these siRNAs exhibited enhanced resistance to the blast disease.Taken.together,our data demonstrate that transgenic approach is a powerful biotechnology in engineering disease resistance in rice.By this approach,resistance genes from other plant species or siRNA and miRNA can all be exploited in engineering resistance against the blast disease.