Abstract
Phytophthora root and stem rot, a destructive disease of soybean [Glycine max (L.) Merr.], is caused by the oomycete Phytophthora sojae. However, how the disease resistance mechanisms of soybean respond to P. sojae infection remains unclear. Previously, we showed that GmWRKY31, which interacts with a sucrose non-fermenting-1(SNF1)-related protein kinase (SnRK), enhances resistance to P. sojae in soybean. Here, we report that the membrane-localized SnRK GmSnRK1.1 is involved in the soybean host response to P. sojae. The overexpression of GmSnRK1.1 (GmSnRK1.1-OE) increased soybean resistance to P. sojae, and the RNA interference (RNAi)-mediated silencing of GmSnRK1.1 (GmSnRK1.1-R) reduced resistance to P. sojae. Moreover, the activities and transcript levels of the antioxidant enzymes superoxide dismutase and peroxidase were markedly higher in the GmSnRK1.1-OE transgenic soybean plants than in the wild type (WT), but were reduced in the GmSnRK1.1-R plants. Several isoflavonoid phytoalexins related genes GmPAL, GmIFR, Gm4CL and GmCHS were significantly higher in “Suinong 10” and GmSnRK1.1-OE lines than these in “Dongnong 50,” and were significantly lower in GmSnRK1.1-R lines. In addition, the accumulation of salicylic acid (SA) and the expression level of the SA biosynthesis-related gene were significantly higher in the GmSnRK1.1-OE plants than in the WT and GmSnRK1.1-R plants, moreover, SA biosynthesis inhibitor treated GmSnRK1.1-R lines plants displayed clearly increased pathogen biomass compared with H2O-treated plants after 24 h post-inoculation. These results showed that GmSnRK1.1 positively regulates soybean resistance to P. sojae, potentially functioning via effects on the expression of SA-related genes and increased accumulation of SA.
Highlights
The sucrose non-fermenting-1(SNF1)-related protein kinases (SnRKs) are key factors in the regulation of energy metabolism, sugar signaling, seed germination, and seedling growth in plants, in addition to stress signaling in a diverse array of eukaryotes (Halford and Hey, 2009; Hey et al, 2010; Coello et al, 2011; Tsai and Gazzarrini, 2014)
Using yeast two-hybrid assays, GmWRKY31 was found to interact with GmSnRK1.1 (Figure 1A), which was further confirmed using a Bimolecular Fluorescence Complementation (BiFC) assay demonstrating that GmSnRK1.1 can interact with GmWRKY31 in the nuclei of Arabidopsis protoplast cells (Figure 1C)
Phylogenetic tree and alignment analyses revealed that GmSnRK1.1 shares 67.91–93.02% identity in overall amino acid sequence with its other plant species homologs, including Lotus japonicus LjSnRK (BAD95888), Manihot esculenta MeSnRK (XP_021604368), Fragaria vesca FvSnRK (XP_004304271), Cucumis sativus CsSnRK (XP_004145003), Vitis vinifera VvSnRK (XM_002283963.1), Cucumis melo CmSnRK (XP_008460108), Pyrus bretschneideri PbSnRK (XP_009360590), Populus trichocarpa PtSnRK (XP_002306053), Morus notabilis MnSnRK (XP_024016886), Vicia faba VfSnRK (AJ971809.1), Pisum sativum PsSnRK (CAI96819.1), Nicotiana attenuate NaSnRK (AAS18877), Populus euphratica PeSnRK (XP_011010304), Arabidopsis thaliana AtSnRK (M93023.1), Daucus carota DcSnRK (XP_017242374), Sorghum bicolor SbSnRK (EF544393.1), Zea mays ZmSnRK (AY486125.1), Solanum tuberosum StSnRK (CAA65244.1), Solanum lycopersicum SlSnRK (NP_001234325.1), and GmSnRK1.1 has the highest similarity with LjSnRK (Supplementary Figures S1B,C)
Summary
The sucrose non-fermenting-1(SNF1)-related protein kinases (SnRKs) are key factors in the regulation of energy metabolism, sugar signaling, seed germination, and seedling growth in plants, in addition to stress signaling in a diverse array of eukaryotes (Halford and Hey, 2009; Hey et al, 2010; Coello et al, 2011; Tsai and Gazzarrini, 2014). Under low-sugar conditions, Arabidopsis SnRK1 was triggered to phosphorylate and inactivate the INDETERMINATE DOMAIN (IDD)-containing transcription factor IDD8, thereby leading to delayed flowering (Jeong et al, 2015) These discoveries show that SnRK1 coordinates the responses to a wide array of abiotic stresses (Baena-González et al, 2007; Lee et al, 2009; Cho et al, 2012; Jeong et al, 2015). No systematic research on the disease-related roles of SnRK1 in another major crop species, soybean (Glycine max), has been reported
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