cDNA transcriptome of Arabidopsis reveals various defense priming induced by a broad-spectrum biocontrol agent Burkholderia sp. SSG

Authors: KONG, PING - Virginia Tech; LI, XIAOPING - Virginia Tech; Gouker, Fred; HONG, CHUANXUE - Virginia Tech

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2022
Publication Date: 3/15/2022
Citation: Kong, P., Li, X., Gouker, F.E., Hong, C. 2022. cDNA transcriptome of Arabidopsis reveals various defense priming induced by a broad-spectrum biocontrol agent Burkholderia sp. SSG. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms23063151.
DOI: https://doi.org/10.3390/ijms23063151

Interpretive Summary: Plant diseases, caused by harmful fungal and bacterial pathogens, are significant threats to plant health and food security. Chemical treatments are primarily used for plant disease management but are costly and have associated environmental and safety concerns. Additionally, pathogens can become resistant to chemical treatments over time rendering them ineffective and leaving plants vulnerable to disease. An alternative disease management strategy is the use of living organisms referred to as biological controls for treatment. Biological controls work by directly killing or suppressing disease infection caused by the harmful pathogens and/or by boosting the plants defense system, allowing plants to fight the disease themselves. A promising biocontrol bacterium, Burkholderia, originally found in boxwood leaves, has been shown to suppress several plant diseases, but it is unknown if it also boosts the plants defense system. In this study, Arabidopsis thaliana plants treated with the biological control Burkolderia were compared to untreated Arabidopsis thaliana plants six and twenty-four hours after treatment to determine if Burkholderia boosted the Arabidopsis thaliana defense system. Results indicate that Burkholderia does indeed boost the plant defense system by triggering an internal plant response that is sustained long after treatment. These findings help us better understand how biocontrols boost plant defenses and how plants fight diseases.

Technical Abstract: Plants applied with a biocontrol agent Burkholderia sp. SSG at a lead time of one week or longer before pathogen inoculation are moderately resistant against a broad spectrum of pathogens, but the resistance mechanism is unclear. Here, we treated Arabidopsis Col-0 and mutant plants, eds16-1, npr1-1, and pad4-1 with and without SSG to determine whether SSG triggers defense priming leading to the protection. Only eds16-1 leaves with SSG became purplish, suggesting the involvement of salicylic acid (SA) in SSG-induced priming. cDNA sequencing Col-0 plants with Oxford Nanopore Technology and differential gene expression analysis showed 120 and 119 differentially expressed genes (DEGs) at 6 and 24 hours post-treatment (hpt) with SSG. Gene set enrichment analysis showed that most of these DEGs encoded responses to biotic, abiotic stimulus or stress. Four of such DEGs had more than two isoforms. Twenty-three DEGs were shared at 6 and 24 hpt, showing four regulation patterns. Functional categorization of these shared DEGs and 44 very significantly upregulated DEGs revealed that SSG triggered various defense priming mechanisms, including phosphate or iron deficiency, modulation of defense-linked SA, jasmonic acid, ethylene, and abscisic acid pathways, defense-related gene regulation, and chromatin modification. The data supports that SSG is an induced systemic resistance (ISR) trigger conferring plant protection upon pathogen encounter.