Identification Of The Blast Resistance Genes In Three Elite Restorer Lines Of Hybrid Rice

Rice is an important cereal crop,and rice blast is one of the major diseases that affect rice production worldwide.Development and use of resistant varieties have been the most effective method to control this disease.More than 100 blast resistance（R）genes have been identified,of which over 40 R genes have already been cloned.Hybrid rice has the advantage of pyramid multiple resistance（R）genes because a hybrid rice cultivar is developed from the cross of a sterile line with a restorer line that can harbor different R genes.Thus,knowing the R genes in an elite line will help the combination of different R genes into a hybrid rice cultivar.Here,we identified the blast R genes in Shu Hui 548（SH548）,Shu Hui 882（SH882）,and Wu Shan Si Miao（WSSM）,three elite restorer lines of hybrid rice that showed resistance to the rice blast in the disease nurseries.The important results of the present study are summarized as follows.1.At controlled laboratory conditions,the three elite restorer lines exhibited resistance to seven blast isolates collected from the Sichuan Basin,and 24 China Rice Blast strains that harbor varieties of different avirulence genes,indicating the broad-spectrum resistance to blast disease.2.The transcripts of multiple known blast R genes were detected by reverse-transcription PCR（RT-PCR）.Sequencing of the expressed R genes indicated that all three accessions harbor broad-spectrum blast resistance genes.SH548 contains Pi2,Pid2,and Ptr,SH882 contains Pikm and Pid2 whereas,WSSM contains Pid2 and Pi9-Type5,a novel functional allele of Pi9.3.This study indicated that upon infection by Magnaporthe oryzae,strong immune responses were boosted in all the three accessions such as increased H₂O₂accumulation,upregulation of WRKY genes,PTI,SA,JA,and mi RNA signaling pathway genes.SH548 showed a differential expression pattern of Os KS4 and Os4g10010 with WSSM.A higher expression pattern of NPR1,AOS2,and PBZ1 in SH548 was observed.PTI pathway was activated in the SH548 and SH882 with the up-regulation of Os CERK1and Os CEBi P in response to chitin treatment.Differential expression pattern of AGO1 genes with up-regulation of AGO1a in SH548 and AGO1b in SH882 and WSSM was observed.In summary,SH548,SH882,and WSSM exhibited a broad-spectrum of blast resistance and contain functional broad-spectrum resistance genes as well.Therefore,they can be exploited in combination with the sterile lines containing the other R genes,and can be used as blast resistance donors in disease-resistance breeding programs.