Browsing by Author "Dou, Daolong"

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    Copy Number Variation and Transcriptional Polymorphisms of Phytophthora sojae RXLR Effector Genes Avr1a and Avr3a
    Qutob, Dinah; Tedman-Jones, Jennifer; Dong, Suomeng; Kuflu, Kuflom; Pham, Hai; Wang, Yuanchao; Dou, Daolong; Kale, Shiv D.; Arredondo, Felipe D.; Tyler, Brett M.; Gijzen, Mark (Public Library of Science, 2009-04-03)
    The importance of segmental duplications and copy number variants as a source of genetic and phenotypic variation is gaining greater appreciation, in a variety of organisms. Now, we have identified the Phytophthora sojae avirulence genes Avr1a and Avr3a and demonstrate how each of these Avr genes display copy number variation in different strains of P. sojae. The Avr1a locus is a tandem array of four near-identical copies of a 5.2 kb DNA segment. Two copies encoding Avr1a are deleted in some P. sojae strains, causing changes in virulence. In other P. sojae strains, differences in transcription of Avr1a result in gain of virulence. For Avr3a, there are four copies or one copy of this gene, depending on the P. sojae strain. In P. sojae strains with multiple copies of Avr3a, this gene occurs within a 10.8 kb segmental duplication that includes four other genes. Transcriptional differences of the Avr3a gene among P. sojae strains cause changes in virulence. To determine the extent of duplication within the superfamily of secreted proteins that includes Avr1a and Avr3a, predicted RXLR effector enes from the P. sojae and the P. ramorum genomes were compared by counting trace file matches from whole genome shotgun sequences. The results indicate that multiple, near-identical copies of RXLR effector genes are prevalent in oomycete genomes. We propose that multiple copies of particular RXLR effectors may contribute to pathogen fitness. However, recognition of these effectors by plant immune systems results in selection for pathogen strains with deleted or transcriptionally silenced gene copies.
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    Phytophthora sojae Avirulence Effector Avr3b is a Secreted NADH and ADP-ribose Pyrophosphorylase that Modulates Plant Immunity
    Dong, Suomeng; Yin, Weixiao; Kong, Guanghui; Yang, Xinyu; Qutob, Dinah; Chen, Qinghe; Kale, Shiv D.; Sui, Yangyang; Zhang, Zhengguang; Dou, Daolong; Zheng, Xiaobo; Gijzen, Mark; Tyler, Brett M.; Wang, Yuanchao (PLOS Pathogens, 2011-11-10)
    Plants have evolved pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) to protect themselves from infection by diverse pathogens. Avirulence (Avr) effectors that trigger plant ETI as a result of recognition by plant resistance (R) gene products have been identified in many plant pathogenic oomycetes and fungi. However, the virulence functions of oomycete and fungal Avr effectors remain largely unknown. Here, we combined bioinformatics and genetics to identify Avr3b, a new Avr gene from Phytophthora sojae, an oomycete pathogen that causes soybean root rot. Avr3b encodes a secreted protein with the RXLR host-targeting motif and C-terminal W and Nudix hydrolase motifs. Some isolates of P. sojae evade perception by the soybean R gene Rps3b through sequence mutation in Avr3b and lowered transcript accumulation. Transient expression of Avr3b in Nicotiana benthamiana increased susceptibility to P. capsici and P. parasitica, with significantly reduced accumulation of reactive oxygen species (ROS) around invasion sites. Biochemical assays confirmed that Avr3b is an ADP-ribose/NADH pyrophosphorylase, as predicted from the Nudix motif. Deletion of the Nudix motif of Avr3b abolished enzyme activity. Mutation of key residues in Nudix motif significantly impaired Avr3b virulence function but not the avirulence activity. Some Nudix hydrolases act as negative regulators of plant immunity, and thus Avr3b might be delivered into host cells as a Nudix hydrolase to impair host immunity. Avr3b homologues are present in several sequenced Phytophthora genomes, suggesting that Phytophthora pathogens might share similar strategies to suppress plant immunity.