Variation in Gene Expression between Two Sorghum bicolor Lines Differing in Innate Immunity Response

Abstract

Microbe associated molecular pattern (MAMPs) triggered immunity (MTI) is a key component of the plant innate immunity response to microbial recognition. However, most of our current knowledge of MTI comes from model plants (i.e., Arabidopsis thaliana) with comparatively less work done using crop plants. In this work, we studied the MAMP triggered oxidative burst (ROS) and the transcriptional response in two Sorghum bicolor genotypes, BTx623 and SC155-14E. SC155-14E is a line that shows high anthracnose resistance and the line BTx623 is susceptible to anthracnose. Our results revealed a clear variation in gene expression and ROS in response to either flagellin (flg22) or chitin elicitation between the two lines. While the transcriptional response to each MAMP and in each line was unique there was a considerable degree of overlap, and we were able to define a core set of genes associated with the sorghum MAMP transcriptional response. The GO term and KEGG pathway enrichment analysis discovered more immunity and pathogen resistance related DEGs in MAMP treated SC155-14E samples than in BTx623 with the same treatment. The results provide a baseline for future studies to investigate innate immunity pathways in sorghum, including efforts to enhance disease resistance.

Characterization of a foxtail mosaic virus vector for gene silencing and analysis of innate immune responses in Sorghum bicolor

“…The publication and improved annotation of the sorghum reference genome (Mace et al, 2013 ; Mullet et al, 2014 ; Xin et al, 2021 ) have facilitated the identification of genes regulating traits of interest to sorghum growers. Numerous candidate genes for improved disease resistance have been identified, largely through differential expression analysis using susceptible and resistant genotypes (Cui et al, 2021 ; Lo et al, 1999 ; Wang et al, 2020 ). However, most sorghum genotypes are recalcitrant to standard transformation methods, presenting a major challenge for gene function validation.…”

“…BTx623 was selected for immune assays because of the robust gene silencing we observed with PDS and Ub (Figure 1 ) and its susceptibility to bacterial and fungal pathogens (Cui et al, 2021 ; Patil et al, 2017 ). Approximately 280–300 bp sequences were selected for VIGS of individual subgroup 8 RLCKs (Table S1 ) using the Sol Genomics Network VIGS Tool ( https://vigs.solgenomics.net/ ) and cloned into FoMV at MCSI in the antisense orientation (Figure 1b ).…”

“…ROS serve as antimicrobial molecules as well as short and long‐distance immune signals from sites of pathogen attack (Lee et al, 2020 ; Sun & Zhang, 2021 ). We therefore monitored ROS production in response to the MAMP flg22, corresponding to a 22 amino acid epitope of bacterial flagellin, known to elicit immune signalling in diverse plants including Arabidopsis, rice, soybean, and sorghum (Chinchilla et al, 2006 ; Cui et al, 2021 ; Takai et al, 2008 ; Wei et al, 2020 ). Silencing of RLCK1 alone, using the FoMV::RLCK1 silencing vector, significantly reduced flg22‐elicited ROS production compared to FoMV‐treated controls (Figure 2c ).…”

“…The greatest reduction in ROS production was observed using the FoMV::RLCK3 construct or when all three VIGS constructs were coinfected (Figure 2c ). Some RLCKs display specificity for PRR complex activation (Rao et al, 2018 ), therefore we additionally monitored ROS production in response to elicitation with chitin, a component of fungal cell walls and a known MAMP in sorghum (Cui et al, 2021 ; Nida et al, 2021 ; Samira et al, 2020 ). Chitin elicited a more robust ROS burst than flg22 (Figure 2c,d ), in line with previous observations in this species (Cui et al, 2021 ).…”

“…Some RLCKs display specificity for PRR complex activation (Rao et al, 2018 ), therefore we additionally monitored ROS production in response to elicitation with chitin, a component of fungal cell walls and a known MAMP in sorghum (Cui et al, 2021 ; Nida et al, 2021 ; Samira et al, 2020 ). Chitin elicited a more robust ROS burst than flg22 (Figure 2c,d ), in line with previous observations in this species (Cui et al, 2021 ). Silencing of RLCK1 alone resulted in a significant reduction in chitin‐elicited ROS production (Figure 2d ).…”