Pi1
Contents
Annotated Information
Introduction
Rice blast caused by Pyricularia grisea (Cooke) Sacc., the anamorphous state of Magnaporthe grisea (T.T. Hebert) Barr, is the most limiting biotic factor for rice production in the world. The blast resistance gene Pi-1(t), originally identified in the cultivar LAC23, an upland cultivar from Liberia within the subspecific isozyme group IV according to Glaszmann’s classification, confers complete resistance to several blast populations from Latin America when combined with the blast resistance genes Pi-2(t) and Pi-33(t). The Pi-1(t) gene confers resistance to all races present in one of the most predominant genetic lineages (SRL-4) from Colombia, while the other two genes confer resistance to all races within two other predominant lineages (SRL-5 and SRL-6), respectively. [2]
The differential reactions to the various blast isolates showed that Pi1 is distinct from other Pik alleles (Pik, Pik-p and Pik-m), as well as from R genes at the Pia and Pi2 loci. Pi1 gave a consistent level of resistance in GD throughout the period 1998–2008, suggesting that it is durable (Fig. 1a). The gene also conferred resistance to a broad range of blast isolates from across China, although it was ineffective against some blast isolates collected from the JL Province (Fig. 1b). [1]
The Pi1 nucleotide sequence has been deposited in GenBank as accession HQ606329. [1]
Location
The location of Pi1 was confined to a region delimited by CRG11-7 and K28, equivalent to a 277-kb stretch of chromosome 11, overlapping with the location of the Pik locus. (Fig. 2).
The K- and N-haplotypes surrounding Pik differ by a large InDel, so both the sequences of cv Nipponbare and BAC clones Ts50A13 and Ts18H12 from cv. Tsuyuake were used as a reference to annotate the candidate region (Fig. 2d). This produced a set of six genes having the expected R gene structure (Fig. 2c, d). The presence/ absence analysis applied to genes Pi1-1 to Pi1-4 showed that Pi1-1N to Pi1-4N were all absent in cv. C101LAC, while Pi1-1C to Pi1-4C were all present (Fig. 2). Thus, cv. C101LAC is the K-haplotype. A perfect association was established between SNP genotype and blast reaction among a set of Pi1 carriers and non-carriers for both Pi1-5C and Pi1-6C (Table 1), promoting these two genes above the four others as candidates for Pi1. Both are orthologs of Pik-m/Pik-p/Pik (Fig. 2d).
Distribution
When the Pi1-5SNP and Pi1-6SNP SNP assays were applied to a large germplasm panel, it was apparent that only the latter was diagnostic for Pi1. The survey of wild rice accessions and indica and japonica landrace and cvs (Tables S2 and S3) showed that Pi1 was only present in two indica cvs (Tetep and C101LAC) and one japonica cv (IRBL1-CL, which was derived from cv. C101LAC). The presence of Pi1 only in the modern cultivar populations suggested that it probably evolved later than Pik-m, Pik-p or Pik. Tetep was bred in SE Asia (Vietnam) and LAC23 (the Pi1 donor to C101LAC and IRBL1-CL) originated in W Africa (Liberia).[1].
Function
The products of major resistance (R) genes recognize and interact with elicitors produced by pathogens, and the proteins encoded by defense-responsive genes initiate signal transduction leading to defense responses of host plants. [3]The Pi1 R gene, derived from the durably resistant West African cv. LAC23, has displayed a high level of durable resistance against blast and was hypothesized to be an allele at the Pik locus.[1].
Through field tests it was found that, on the background of Jin 23B, the pyramided three-gene Pi1 + Pi2 + D12 lines exhibited a higher level of resistance than two-gene lines Pi1 + Pi2, Pi1 + D12, and Pi2 + D12. These two-gene lines also showed a higher level of resistance than single-gene introgression line. Pi1 might be an incomplete dominance gene. Pi1, Pi2, and D12 have great potential for use in hybrid rice breeding. [4]
Evolution
Pi1 is now the fourth cloned and characterized allele at this complex locus. The Pik locus has proven valuable to rice breeders concerned with blast resistance, as most alleles impart broad spectrum and durable resistance. Pi1 has been used in a number of rice breeding programs. For example, it was combined with Pi2 and Pita by IRRI (Hittalmani et al. 2000) for use in both the Philippines and India; by Fuentes et al. (2008) in Latin America; in Europe by Tacconi et al. (2010), and in China it is regarded as having great potential for achieving broad spectrum and durable resistance. The Pi1 allele is effective against many, but not all, isolates collected from the broad range of cropping seasons and regions. The presence of Pi1 only in both modern cultivars suggests that it evolved relatively recently, unlike Pik-p which predates the domestication of rice, and Pik and Pik-m, both of which evolved somewhat after rice domestication. [1].
Labs working on this gene
• State Key Laboratory for Conservation and Utilization of Subtropic Agrobioresources, Laboratory of Plant Resistance and Genetics, College of Natural Resources and Environmental Sciences, South China Agricultural University, Guangzhou 510642, China
• Escuela de Biolog ́ıa, Facultad de Ciencias, Universidad Industrial de Santander (UIS), Apartado Ae ́reo 678, Bucaramanga, Colombia
• National Key Laboratory of Crop Genetic Improvement, National Center of Crop Molecular Breeding, Huazhong Agricultural University, 430070, Wuhan, China
• International Rice Research Institute, P.O. Box 933, Manila, Philippines
• National Institute of Agricultural Science and Technology, Rural Development Administration, Suweon 441-100, Korea
• Department of Plant Breeding & Biometry, Cornell University, Ithaca, NY 14853, U.S.A.
• present address: Department of Agronomy, College of Agriculture, Chungnam National University, Yusong, Taejon 305-764, Korea
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Lixia Hua, Jianzhong Wu, Caixia Chen, Weihuai Wu, Xiuying He, et al. (2012) The isolation of Pi1, an allele at the Pik locus which confers broad spectrum resistance to rice blast. Theor Appl Genet 125:1047–1055.
- ↑ Jorge Luis Fuentes, Fernando Jose ́ Correa-Victoria, Fabio Escobar, Gustavo Prado, Girlena Aricapa, et al. (2008) Identification of microsatellite markers linked to the blast resistance gene Pi-1(t) in rice. Euphytica 160: 295–304.
- ↑ N. Wen, Z. Chu, S. Wang. (2003) Three types of defense-responsive genes are involved in resistance to bacterial blight and fungal blast diseases in rice. Mol Gen Genomics 269: 331–339.
- ↑ Haichao Jiang, Yutao Feng, Liang Bao, Xin Li, Guanjun Gao, et al. (2012) Improving blast resistance of Jin 23B and its hybrid rice by marker-assisted gene pyramiding. Mol Breeding 30: 1679-1688.
