The Phytophthora sojae Avirulence Locus Avr3c Encodes a Multi-Copy RXLR Effector with Sequence Polymorphisms among Pathogen Strains

Abstract

Root and stem rot disease of soybean is caused by the oomycete Phytophthora sojae. The avirulence (Avr) genes of P. sojae control race-cultivar compatibility. In this study, we identify the P. sojae Avr3c gene and show that it encodes a predicted RXLR effector protein of 220 amino acids. Sequence and transcriptional data were compared for predicted RXLR effectors occurring in the vicinity of Avr4/6, as genetic linkage of Avr3c and Avr4/6 was previously suggested. Mapping of DNA markers in a F2 population was performed to determine whether selected RXLR effector genes co-segregate with the Avr3c phenotype. The results pointed to one RXLR candidate gene as likely to encode Avr3c. This was verified by testing selected genes by a co-bombardment assay on soybean plants with Rps3c, thus demonstrating functionality and confirming the identity of Avr3c. The Avr3c gene together with eight other predicted genes are part of a repetitive segment of 33.7 kb. Three near-identical copies of this segment occur in a tandem array. In P. sojae strain P6497, two identical copies of Avr3c occur within the repeated segments whereas the third copy of this RXLR effector has diverged in sequence. The Avr3c gene is expressed during the early stages of infection in all P. sojae strains examined. Virulent alleles of Avr3c that differ in amino acid sequence were identified in other strains of P. sojae. Gain of virulence was acquired through mutation and subsequent sequence exchanges between the two copies of Avr3c. The results illustrate the importance of segmental duplications and RXLR effector evolution in the control of race-cultivar compatibility in the P. sojae and soybean interaction.

Isolation and characterization of Bacillus altitudinis JSCX-1 as a new potential biocontrol agent against Phytophthora sojae in soybean [Glycine max (L.) Merr.]

“…To test the antagonistic effects of JSCX-1 in vivo, the experiments were performed on mature soybean leaves and etiolated seedlings (Dong et al 2009). JSCX-1 was inoculated as above, soybean leaves and etiolated seedlings were fully submerged in cell suspensions of JSCX-1 (OD 600 = 1) or sterile water for 1 min, then the center of a G. max leaf or etiolated seedling was infected with a small piece of P. sojae mycelial disk from the edge of a 5-day-old colony, mycelial-side down.…”

Two Host Cytoplasmic Effectors Are Required for Pathogenesis of Phytophthora sojae by Suppression of Host Defenses

“…To examine the pathogenicity of the silenced transformants, we inoculated etiolated soybean seedlings (Dong et al, 2009) of cv Williams, which is susceptible to most strains of P. sojae, including P6497. The expression deficiency of these two CRN effectors resulted in a significant reduction of virulence (Fig.…”

“…The pathogenicity phenotypes of selected transformants were determined by inoculation of etiolated soybean (Glycine max) seedlings (Dong et al, 2009) and by hypocotyl inoculation (Tyler et al, 1995). For inoculation of etiolated soybean seedlings, cv Williams (rps) was used.…”

Transcriptional Programming and Functional Interactions within the Phytophthora sojae RXLR Effector Repertoire

“…Thus, presence of the RXLR-dEER motifs in the Avh proteins makes them all candidate effectors. The importance of the Avh proteins is underlined by the finding that 10 recently cloned oomycete Avr genes all encode RXLR-dEER proteins, including Avr1a, Avr3a, Avr3c, and Avr4/6 from P. sojae (Shan et al, 2004;Dong et al, 2009;Qutob et al, 2009;Dou et al, 2010), Avr2, Avr4, Avr-blb1, and Avr-blb2 from P. infestans van Poppel et al, 2008;Vleeshouwers et al, 2008;Oh et al, 2009), and ATR1 and ATR13 from H. arabidopsidis (Allen et al, 2004;Rehmany et al, 2005). Due to selection pressure from the hosts, the avirulence genes show extensive variations, including amino acid changes indicative of strong positive selection, gene truncations and deletions, and transcriptional silencing (Jiang et al, 2008;Qutob et al, 2009).…”