Identification and Expression Pattern Analysis of Bacterial Blight Resistance Genes in Oryza officinalis Wall ex Watt Under Xanthomonas oryzae Pv. oryzae Stress

Abstract

Background Bacterial blight (BB) caused by Xanthomonas oryzae Pv. oryzae (Xoo) is one of the most serious diseases of rice worldwide. Oryza officinalis Wall ex Watt, harboring abundant genetic diversity and disease resistance features, are important resources of exploring resistance genes with broad-spectrum resistance to BB. However, the molecular mechanisms and genes of BB resistance in O. officinalis have been rarely explored. Results Here, the BB resistance of four different origin O. officinalis populations in Yunnan were identified by seven representative hypervirulent Xoo races, which exhibited different BB resistance among four populations, in which the BB resistance of the Gengma_Lincang population was the strongest. In addition, the pathogenetic ability of seven Xoo races to O. officinalis was different in that the pathogenicity of PXO99 was stronger than that of C5. There were no remarkable differences in leaf microstructures among four O. officinalis populations, revealing the differences in resistance of four O. officinalis to BB are caused by the endogenous resistance genes. Furthermore, our results proved that there were no nine cloned BB resistance genes in four populations but possessed dominant Xa5, dominant Xa13, and recessive xa3/xa26 homologous alleles of xa5, xa13, and Xa3/Xa26 resistance genes. These three homologous genes were isolated and cloned from four populations and named OoXa5, OoXa13, and Ooxa3/xa26. The expression profile revealed that the expression levels of OoXa13 and Ooxa3/xa26 were significantly down-regulated under PXO99 and C5 stress, especially in the Gengma_Lincang population, suggesting the O. officinalis might enhance BB resistance by down-regulating the expression level of OoXa13 and Ooxa3/xa26. Conclusion The BB resistance genes of O. officinalis had its own characteristics by expression pattern and BLAST analysis of OoXa5, OoXa13, and Ooxa3/xa26, which indicated that there might be new genes or molecular mechanism of BB resistance in O. officinalis. Our studies provided a solid foundation and reference for revealing the molecular mechanism of BB resistance in O. officinalis.

Identification of bacterial blight resistance genes in rice landraces from Yunnan Province, China

“…Some previous studies have reported phenotypic resistance to BB in rice by the leaf-clipping method (Fred et al 2016;Jiang et al 2019). Molecular markers can greatly facilitate the development of new disease resistant materials, and effectively detect the presence of BB resistance genes in rice (Ullah et al 2012;Hur et al 2013).…”

“…All strains were cultured on Nutrient Agar medium by 28℃ for 48 h, then resuspended in double distilled water, and diluted to OD 600 nm = 0.8 for inoculation by using the NanoDrop2000. Each rice accession at booting stage (panicle development) was respectively inoculated with Xoo strains by the leafclipping method at 15:00 ~ 17:00 (Jiang et al 2019). Three replicates (three individual plants) for each accession were designed for each Xoo strain with five leaves inoculated per plant.…”

“…Molecular markers within closely linked to the target genes can be used to identify germplasm with one or more resistance genes (Perumalsamy et al 2010). The application of gene-linked/specific molecular markers should be complemented by gene homologous cloning method and sequences analysis to effectively analyze the type of resistance genes (Jiang et al 2019).…”

The barley leaf rust resistance gene Rph3 encodes a putative executor protein

“…The inducible expression of Rph3. Most cloned disease resistance genes are expressed constitutively 60,61 . Constitutive expression was observed in genes conferring resistance to various pathogens, including bacteria [62][63][64] and fungi [65][66][67][68] .…”

OrMKK3 Influences Morphology and Grain Size in Rice

“…Recent studies have isolated and characterized several genes for disease resistance from O. officinalis Wall. ex Watt (Jiang et al 2019 ), however, the identities of genes for grain size and plant architecture are unknown.…”