Abstract
Shading in the intercropping system is a major abiotic factor which influences soybean growth and development, while soybean mosaic virus (SMV) is a biotic factor that limits the yield and quality of soybean. However, little is known about the defense response of soybean to SMV in the shade. Thus, in the current study, both intensity and quality (red:far-red, R:FR) of the light were changed to simulate the shaded environment and comparative transcriptome analysis was performed. Morphologically, plant growth was inhibited by SMV, which decreased 35.93% of plant height and 8.97% of stem diameter in the shade. A total of 3548 and 4319 differentially expressed genes (DEGs) were identified in soybean plants infected with SMV under normal light and in the shade. Enrichment analysis showed that the plant defense-related genes were upregulated under normal light but downregulated in the shade. Pathways that were repressed include plant-pathogen interaction, secondary metabolism, sugar metabolism, and vitamin metabolism. In addition, genes associated with signaling pathways such as salicylic acid (SA), jasmonic acid (JA), and ethylene (ETH) were also downregulated in the shade. A qRT-PCR assay of 15 DEGs was performed to confirm transcriptome results. According to our knowledge, this is the first report on soybean response to dual stress factors. These results provide insights into the molecular mechanisms in which soybean plants were infected with SMV in the shade.
Highlights
Due to the advantages of interspecific complementation, nutrient exchange, marginal effects, and high biodiversity, maize-soybean strip intercropping has become the main cultivation model for soybean in southwestern China [1,2,3]
NS and NC refer to Soybean mosaic virus (SMV) infection and control, respectively, under normal light, while LS and LC refer to SMV infection and control, respectively, in the shade
To further confirm the gene expression pattern obtained from RNA-Seq, 15 differentially expressed genes (DEGs) were selected for qRT-PCR, including Phytochrome kinase substrate 1 (GLYMA_01G046600), A-ARR (GLYMA_04G247800), BAK1 (GLYMA_05G119500), AUX1 (GLYMA_12G030900), PIF4 (GLYMA_14G032200), pathogenesis-related 1 (PR1) (GLYMA_15G062400, GLYMA_15G062500, and GLYMA_15G062700), PhyB (GLYMA_15G140000), JAR1 (GLYMA_16G026900), HSP70 (GLYMA_17G072400), WRKY62 (GLYMA_18G056600), PhyA (GLYMA_20G090000), DELLA (GLYMA_20G200500), and ERF1 (GLYMA_20G203700)
Summary
Due to the advantages of interspecific complementation, nutrient exchange, marginal effects, and high biodiversity, maize-soybean strip intercropping has become the main cultivation model for soybean in southwestern China [1,2,3]. By studying the soybean V1 leaves (the first trifoliate leaf) after infection with SMV at 7, 14, and 21 days post-inoculation (dpi), it was found that the defense response to the virus was activated at later stage, which helped the virus to establish a systemic infection [14]. This is consistent with the study by Zhao et al [15]. In the case of reduced light intensity and light quality, the defense response of soybean to SMV, especially at the transcriptional level, has not been studied yet. To the best of our knowledge, this is the first transcriptome study on light-regulated soybean response to virus infection
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