Strain Specific Factors Control Effector Gene Silencing in Phytophthora sojae

Area of Science:

• Plant Pathology
• Molecular Genetics
• Agronomy

Background:

• Phytophthora sojae is a major soybean pathogen.
• The Avr3a effector gene in P. sojae triggers immunity in soybean plants with the Rps3a resistance gene.
• Avr3a expression determines P. sojae virulence or avirulence on Rps3a soybean plants.

Purpose of the Study:

• To investigate the inheritance of Avr3a gene expression and its associated avirulence trait in Phytophthora sojae.
• To understand the mechanisms underlying transgenerational gene silencing of Avr3a.

Main Methods:

• Genetic crosses and self-fertilizations of Phytophthora sojae strains.
• Analysis of small RNA in parental strains and hybrid progeny.
• Phenotypic assessment of virulence and avirulence traits in progeny.

Main Results:

• A cross between P. sojae strains ACR10 and P7076 induced meiotically stable transgenerational gene silencing of Avr3a, persisting to the F5 generation.
• Test-crosses of F1 progeny with P6497 released the Avr3a silencing, leading to variable gene expression and trait penetrance.
• Small RNA presence was necessary but not sufficient for Avr3a gene silencing, and inheritance patterns could not be explained by parental imprinting or heterozygosity.

Conclusions:

• Inheritance of the Avr3a gene silenced phenotype in P. sojae is dependent on strain-variable factors.
• The study highlights complex epigenetic regulation influencing pathogen virulence and host-pathogen interactions.