Abstract
Phytophthora sansomeana
was detected in several soybean root rot surveys in the United States, alongside another well-studied oomycete,
P. sojae
. We compared the transcriptomic responses among three
P. sansomeana
isolates that differed in aggressiveness and
P. sojae
isolate OH25 with the most aggressive
P. sansomeana
isolate in a moderately susceptible soybean using dual host-pathogen RNA-Seq. At each time point, the relative pathogen read abundance was higher following inoculation with
P. sojae
than
P. sansomeana.
Differentially expressed genes (DEGs) relative to mycelial samples were more pronounced for
P. sojae
than for
P. sansomeana
. More than a hundred genes were significantly upregulated across all three
P. sansomeana
isolates for all three time points. These included genes associated with cell wall degradation, jacalin-like lectin, NmrA-like family, one RxLR, and amino acid auxin permease family. For
P. sansomeana
, more genes annotated as crinkling- and necrosis-inducing were downregulated, and fewer necrosis-inducing peptides were upregulated compared with
P. sojae
, which could explain in part the difference in necrosis symptom development between the two species. Additionally,
P. sojae
had more DEGs associated with pathogenicity than the most aggressive
P. sansomeana
isolate. Several key defense pathways were upregulated in soybean earlier in response to the three
P. sansomeana
isolates than to
P. sojae
, including glucosinolate and glutathione biosynthesis, sulfur and tropane, and piperidine and pyridine alkaloid metabolism, which may also explain the reduced lesion sizes. These results provide a framework for using effector screening to select for effective host resistance against populations of both
P. sansomeana
and
P. sojae
.