Os12g0476200
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Xa25(Os01g0136400) is a new dominant gene for bacterial blight resistance in rice, which conferred resistance to Philippine race 9 (PXO339) of X.
Contents
Annotated Information
Function
The xa25, localized in the centromeric region of chromosome 12(see Fig. 1), mediates race-specific resistance to Xoo strain PXO339 at both seedling and adult stages by inhibiting Xoo growth[1]. This gene conferred resistance to Philippine race 9 (PXO339) of X. oryzae pv. oryzae in both seedling and adult stages[2]. It encodes a protein of the MtN3/saliva family, which is prevalent in eukaryotes, including mammals. Transgenic plants carrying dominant Xa25 was analysed for its responses to other Xoo strains at both seedling and adult stages. In seedling stage, the wild-type Minghui 63 carrying dominant Xa3/Xa26 and recessive xa25 was resistant to PXO339 and susceptible to PXO61, PXO341 and PXO99. The transgenic plants showed significantly increased susceptibility (P < 0.01) to PXO339 as compared with the wild-type and the susceptible control plants (Zhenshan 97) and had the same level of susceptibility to PXO61, PXO341 and PXO99 (see Fig. 2)[1]. In the adult stage, the wild-type Minghui 63 was resistant to PXO339, moderately resistant to PXO61 and PXO341, and susceptible to PXO99 . Similar to the seedling stage, the transgenic plants only showed significantly increased susceptibility (P < 0.01) to PXO339 but not Xoo strains PXO61, PXO341 and PXO99 as compared with wild-type plants at adult stage (see Fig. 2). These results suggest that the recessive xa25 confers race-specific resistance to PXO339 at both seedling and adult stages.
Expression
Transformation of the dominant Xa25 into a resistant rice line carrying the recessive xa25 abolished its resistance to PXO339. The encoding proteins of recessive xa25 and its dominant allele Xa25 have eight amino acid differences. The expression of dominant Xa25 but not recessive xa25 was rapidly induced by PXO339 but not other Xoo strain infections. The nature of xa25-encoding protein and its expression pattern in comparison with its susceptible allele in rice–Xoo interaction indicate that the mechanism of xa25-mediated resistance appears to be different from that conferred by most of the characterized R proteins.
Ⅰ Dominant Xa25 but not recessive xa25 is specifically induced by PXO339
Xoo strain PXO339 induced the expression of dominant Xa25 in Zhenshan 97 but not recessive xa25 in Minghui 63 in seedling stage (Fig. 3a)[1].Other Xoo strains (PXO61,PXO99 and PXO341) did not influence the expression of xa25 and Xa25 nor did PXO339 induce the recessive xa25 in resistant Zhonghua 11, Mudanjiang 8 and Nipponbare (Fig. 3b). PXO339 also induced dominant Xa25 but not recessive xa25 in adult stage (Fig. 3c).The consistency of PXO339-regulated race-specific susceptibility and PXO339-induced Xa25 expression suggests that the activation of dominant Xa25 may be associated with susceptibility. The Xa25 promoter (approximately 1.11 kb upstream of the transcription initiation site) from susceptible rice variety Zhenshan 97 was different from xa25 promoters from resistant rice varieties Minghui 63, Zhonghua 11, Nipponbare and Mudanjiang 8 because of nucleotide substitutions, insertions and deletions. The xa25 promoters from Nipponbare and Mudanjiang 8 had identical sequence but different from the xa25 promoters from Minghui 63 and Zhonghua 11. In addition, the xa25 promoters from Minghui 63 and Zhonghua 11 are also different from each other. However, seven polymorphic sites, -1117 (T/C), -1075 (T/C), -663 (deletion/T), -248 (A/G), -56 (C/G), -40 (G/T) and -28 (A/deletion) according to the nucleotide position in Minghui 63, between the promoters of recessive xa25 from the four resistant rice varieties and dominant Xa25 from susceptible Zhenshan 97, were identified. This result suggests that the differential expression of dominant Xa25 and recessive xa25 in response to PXO339 infection may be associated with their promoter difference.
Ⅱ Recessive xa25 and dominant Xa25 encode different proteins
the coding regions of the recessive and dominant alleles were interrupted by five introns . The recessive xa25 alleles in Minghui 63, Zhonghua 11, Mudanjiang 8 and Nipponbare putatively encode identical protein consisting of 296 amino acids.The dominant Xa25 putatively encodes proteins consisting of 293 amino acids. In addition to the size difference, the two proteins have five-residue substitutions . These results suggest that the different functions of recessive xa25 and dominant Xa25 may also be associated with the differences in their encoding proteins.
Ⅲ Developmental stage influences xa25-mediated resistance
There is a report that xa25/Xa25(t) dominantly regulated resistance to Xoo strain PXO339 in a mapping population at adult stage,but the present results reveal that xa25 recessively regulate resistance to PXO339 in a similar mapping population at seedling stage[3].
Evolution
Ⅰ Recessive xa25 belongs to the MtN3/saliva family
the Os12g29220 allele in resistant Minghui 63 is the recessive xa25.The xa25 confers resistance by inhibiting Xoo growth. Because the resistance of Minghui 63 to Xoo strain PXO339 was compromised by expression of dominant Xa25,the previously named R gene Xa25(t) that dominantly conferred Minghui 63 resistance to PXO339[3] should be the same gene as the recessive xa25.
Ⅱ The recessive xa25 is the same as Xa25(t)
xa25 is a recessive R gene at both seedling (Figs 2 & 3) and adult (Fig. 2) stages. The recessive xa25 is the same gene as previously named Xa25(t)[3]. However, xa25 was recessively regulated at seedling stage but dominantly regulated at adult stage [thus named Xa25(t) in Chen et al. 2002]. The inconsistent results of the genetic analyses may have the following explanations. Firstly, the recessive xa25 may be an R gene with the characteristics of dominance reversal. Rice plants carrying xa25/Xa25(t) have the same characteristic as the rice varieties carrying R genes with the nature of dominance reversal reported previously [4] [5]. Secondly, development-associated minor resistance quantitative trait loci (QTLs) may influence the function of the recessive xa25.This hypothesis is supported by the characteristic of another rice R gene Xa3/Xa26 for Xoo resistance. Xa3/Xa26 has a dosage effect that is regulated by rice development; this dosage effect is associated with enhanced expression of defence-responsive genes OsWRKY13 and NH1 [6]. OsWRKY13 and NH1 function as minor resistance QTLs in rice–pathogen interactions [7][8] .
Ⅲ MtN3/saliva-type proteins may have different biochemical functions
The recessive xa25 belongs to the MtN3/saliva gene family. The only known structure of xa25/Xa25 proteins are MtN3/saliva domain. MtN3/saliva family proteins are prevalent in eukaryotes including mammals [9], suggesting that they may have important roles in the physiological and developmental activities of eukaryotes. Rice susceptible protein Xa13 interacts with rice copper transporter 1 (COPT1) and COPT5 to remove copper from xylem vessels in the rice-Xoo interaction. The removal of copper from xylem may be associated with transporting copper into cells, because only the coexpression of the three plasma membrane proteins could complement the phenotype of yeast mutant that lacked the functions of copper transporters for copper uptake [10]. The Xa13 (also named OsSWEET11) functions as a low-affinity glucose transporter in mammalian cells and oocytes [11]. These results suggest that MtN3/saliva-type proteins may have different biochemical functions. The rice MtN3/saliva gene family consists of at least 23 paralogs [11].The encoding proteins of xa25/Xa25 are most closely related to OsSWEET14 (also named Os11N3) based on the phylogenetic analysis (Fig. 4). The OsSWEET14/Os11N3 functions as a low-affinity transporter to mediate glucose efflux in mammalian cells and oocytes; it is suggested that this function of OsSWEET14/Os11N3 may be used by pathogens for nutritional gain [11]. Further study is required to elucidate whether xa25/Xa25 is also involved in sugar transporter in rice-Xoo interaction.
Labs working on this gene
1.National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China
2.National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
3.National Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China
4. College of Life and Environment Sciences, Shanghai Normal University, Shanghai 200234, China
References
- ↑ 1.0 1.1 1.2 Qingsong Liu, Meng Yuan, Yan Zhou, Xxianghua Li, Jinghua Xiao, Shiping Wang.(2011) A paralog of the MtN3/saliva family recessively confers race-specific resistance to Xanthomonas oryzae in rice. Plant, Cell & Environment 34(11): 1958-1969.
- ↑ Huilan Chen, Shiping Wang, Qifa Zhang(2002). New Gene for Bacterial Blight Resistance in Rice Located on Chromosome 12 Identified from Minghui 63, an Elite Restorer Line. Phytopathology, 92(7): 750-754.
- ↑ 3.0 3.1 3.2 Chen H.,Wang S. and Zhang Q. (2002) . New gene for bacterial blight resistance in rice located on chromosome 12 identified from Minghui 63, an elite restorer line. Phytopathology ,92: 750–754.
- ↑ Sidhu G.S. And Khush G.S. (1978) Dominant reversal of a bacterial blight resistance gene in some rice cultivars. Phytopathology 68:461–463.
- ↑ Zhao X.P., Zhang D.P. And Xie Y.F.(1986) Study of dominance reversal of rice bacterial blight resistance genes.Hereditas 8: 5–9.
- ↑ Cao Y., Ding X., Cai M., Zhao J., Lin Y., Li X., Xu C. and Wang S.(2007) The expression pattern of a rice disease resistance gene Xa3/Xa26 is differentially regulated by the genetic backgrounds and developmental stages that influence its function. Genetics 177: 523–533.
- ↑ Hu K., Qiu D., Shen X., Li X. & Wang S. (2008) Isolation and manipulation of quantitative trait loci for disease resistance in rice using a candidate gene approach. Molecular Plant 1: 786–793.
- ↑ Kou Y., Li X., Xiao J. and Wang S. (2010) Identification of genes contributing to quantitative disease resistance in rice. Science China Life Sciences 53: 1263–1273.
- ↑ Guan Y.F., Huang X.Y., Zhu J., Gao J.F., Zhang H.X. and Yang Z.N.(2008) RUPTURED POLLEN GRAIN1, a member of the MtN3/saliva gene family, is crucial for exine pattern formation and cell integrity of microspores in Arabidopsis. Plant Physiology 147: 852–863.
- ↑ Yuan M., Chu Z., Li X., Xu C. & Wang S. (2010) The bacterial pathogen Xanthomonas oryzae overcomes rice defenses by regulating host copper redistribution. The Plant Cell 22: 3164–3176.
- ↑ 11.0 11.1 11.2 Chen L.Q., Hou B.H., Lalonde S., et al. (2010) Sugar transporters for intercellular exchange and nutrition of pathogens. Nature 468, 527–532.
