Auxin Profiling and GmPIN Expression in Phytophthora sojae−Soybean Root Interactions

Abstract

Auxin (indole-3-acetic acid, IAA) has been implicated as a susceptibility factor in both beneficial and pathogenic molecular plant-microbe interactions. Previous studies have identified a large number of auxin-related genes underlying quantitative disease resistance loci (QDRLs) for Phytophthora sojae. Thus, we hypothesized that auxin may be involved the P. sojae-soybean interaction. The levels of IAA and related metabolites were measured in mycelia and media supernatant as well as in mock and inoculated soybean roots in a time course assay. The expression of eleven soybean Pin-formed (GmPIN) auxin efflux transporter genes was also examined. Tryptophan, an auxin precursor, was detected in the P. sojae mycelia and media supernatant. During colonization of roots, levels of IAA and related metabolites were significantly higher in both moderately resistant Conrad and moderately susceptible Sloan inoculated roots compared to mock controls at 48 hours post inoculation (hpi) in one experiment and at 72 hpi in a second, with Sloan accumulating higher levels of the auxin catabolite IAA-Ala than Conrad. Additionally, one GmPIN at 24 hpi, one at 48 hpi, and three at 72 hpi had higher expression in inoculated compared to the mock control roots in Conrad. The ability of resistant cultivars to cope with auxin accumulation may play an important role in quantitative disease resistance. Levels of jasmonic acid (JA), another plant hormone associated with defense responses, were also higher in inoculated roots at these same time points, suggesting that JA also plays a role during the later stages of infection.

Identification of Candidate Genes for a Major Quantitative Disease Resistance Locus From Soybean PI 427105B for Resistance to Phytophthora sojae

“…We found specific and significant increase in JA accumulation in the inoculated treatment of susceptible NILs at 24 hai. It is unclear whether the accumulation of JA is due to the successful colonization of P. sojae or if, like some of our earlier studies (Stasko et al, 2020 ), increased JA aids in successful colonization by P. sojae . While our data do not show a concomitant response in SA accumulation, the clear increase in JA in response to inoculation in susceptible NILs combined with the known antagonistic relation could implicate QDRL-18 as a negative regulator of plant immunity.…”

“…Indeed, SA, rather than JA, is generally the phytohormone associated with contributing resistance to hemibiotrophic pathogens (Robert-Seilaniantz et al, 2007 ; Pan et al, 2016 ). However, a cultivar with high levels of quantitative resistance was not affected by high levels of auxin nor its precursors; JA was proposed as playing a role in the later stages of infection (Stasko et al, 2020 ).…”

Comparative transcriptome profiling identifies maize line specificity of fungal effectors in the maize–Ustilago maydis interaction

“…Previous studies have identified a large number of auxin‐related genes that underlie QDR. For example, in the soybean– Phytophthora sojae interaction, auxin catabolite accumulation differed between a relatively resistant and a more susceptible soybean cultivar, and the ability of resistant cultivars to cope with auxin accumulation was suggested to play an important role in QDR in this pathosystem (Stasko et al ., 2020). In maize, cloning of the causal gene of the Gibberella stalk rot resistance QTL qRfg2 identified ZmAuxRP1, which encodes a plastid stroma‐localised auxin‐regulated protein, presumably modulating auxin biosynthesis (Ye et al ., 2019).…”

Transcriptome analysis in the maize-Ustilago maydisinteraction identifies maize-line-specific activity of fungal effectors

“…Previous studies have identified a large number of auxin-related genes that underlie QDR. For example in the soybean- Phytophthora sojae interaction, auxin catabolite accumulation differed between a relatively resistant and a more susceptible soybean cultivar, and the ability of resistant cultivars to cope with auxin accumulation was suggested to play an important role in QDR in this pathosystem (Stasko et al 2020). In maize, cloning of the causal gene of the Giberella stalk rot resistance QTL qRfg2 identified ZmAuxRP1, which encodes a plastid stroma-localised auxin-regulated protein, presumably modulating auxin biosynthesis (Ye et al 2019).…”