GSE137263
A Transcriptional Regulatory Network of Rsv3-mediated Extreme Resistance Against Soybean Mosaic Virus
Resistance (R) genes are very effective for disease control in plants. Current research shows that R genes predominantly function by inducing a hypersensitive reaction (HR), which results in localized cell death thought to restrict pathogen spread. Some R genes elicit a more atypical response where resistance is not associated with HR or the associated gene expression changes, termed extreme resistance (ER). The molecular regulatory mechanism underlying ER is largely unexplored. One of the few known, naturally occurring, instances of ER is resistance derived from the soybean Rsv3 gene, which confers resistance against the most virulent strains of soybean mosaic virus (SMV). To discern the regulatory mechanism underlying the Rsv3-mediated ER reaction, we generated a gene regulatory network using transcriptomic data from a time course comparison of SMV-G7-infected resistant (L29, Rsv3-genotype) and susceptible (Williams82, rsv3-genotype) soybean cultivars. We identified putative interactions between transcription factors (TFs) regulating gene expression in hormone regulatory pathways, such as abscisic acid (ABA) and jasmonic acid (JA). This is consistent with the demonstrated involvement of these pathways in Rsv3-mediated resistance. We found significant enrichment for the G-box motif (“CACGTG”) among genes implicated in ABA- and JA-related activities. This motif is specifically recognized by MYC2, which is a master regulator of ABA and JA signaling. Our network identified a MYC2 TF encoded by Glyma.07G051500 as a putative transcriptional regulator whose expression was significantly down-regulated in L29. This correlated with the down-regulation of expression of genes involved in ABA and JA processes. Our results suggest an important function for Glyma.07G051500 in ABA and JA derived defense signaling. Additionally, our regulatory network found other putative TFs with differential expression, such as MYBs and ERFs, which may also be involved in regulating ABA and JA signaling for defense. The regulatory network presented here offers new insights into the regulation of the molecular defense mechanism underlying Rsv3-mediated ER against SMV. Overall design: The soybean cultivars 'L29' (Rsv3-genotype; resistant) and 'Williams82' (rsv3-genotype; susceptible) were used in this study. The Rsv3-genotype confers ER to the most virulent strains of SMV. Thus the goal of this study was to investigate the regulation of the Rsv3-mediated ER molecular defense mechanism against SMV. Plants were grown in controlled greenhouse conditions and inoculated at first, fully, expanded trifoliolate stage with SMV strain G7 (SMV-G7). Unifoliolate leaves were dusted with carborundum powder and rubbed with SMV-G7 inoculum. The inoculated unifoliolate leaves were collected at 0, 2, 4, 6, and 8 hours post inoculation (hpi) and stored at -80°C until RNA extraction. High-quality total RNA (RNA >7.0) was extracted from frozen samples using RNeasy Plant Mini Kit (QIAGEN, Hilden, Germany) with on-column DNase digestion (QIAGEN, Hilden, Germany). A total of 20 mRNA libraries (= 2 cultivars x 5 time-points x 2 biological replicates) were prepared from duplicate RNA samples of each line at each time point and sequenced as 150PE with Illumina HiSeq4000 (Illumina, San Diego, CA) at Novogene, Sacramento, CA.