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 11 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 with mock controls at 48 h postinoculation (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 with 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.

生长素（吲哚-3-乙酸，IAA）被认为是有益和致病分子植物与微生物相互作用的易感因子。先前的研究已经鉴定出大豆疫霉定量抗病位点（QDRL）的大量生长素相关基因。因此，我们假设生长素可能参与酱油-大豆相互作用。通过时程测定，测量了菌丝体和培养基上清液以及模拟和接种的大豆根中 IAA 和相关代谢物的水平。还检测了 11 个大豆Pin 型( GmPIN ) 生长素外排转运蛋白基因的表达。在酱油菌丝体和培养基上清液中检测到色氨酸，一种生长素前体。在根定植过程中，与模拟对照相比，中度抗性 Conrad 和中度易感 Sloan 接种的根中 IAA 和相关代谢物的水平在一次实验中接种后 48 小时 (hpi) 和第二次接种后 72 hpi 时均显着升高，其中 Sloan 积累生长素分解代谢物 IAA-Ala 的水平高于 Conrad。此外，与 Conrad 中的模拟对照根相比，接种后 24 hpi 的 1 个GmPIN 、48 hpi 的 1 个和 72 hpi 的 3 个 GmPIN 的表达量更高。抗性品种应对生长素积累的能力可能在定量抗病性中发挥重要作用。在同一时间点，接种的根中茉莉酸（JA）的水平也较高，茉莉酸（JA）是另一种与防御反应相关的植物激素，这表明 JA 在感染的后期也发挥了作用。