Abstract
Transcriptomic studies provide valuable insights into the molecular mechanisms underlying plant responses to various stimuli, including phytohormones such as salicylic acid (SA) and jasmonic acid (JA), which are produced in response to attack by biotrophic and necrotrophic pathogens, respectively. Interactions between SA and JA signaling pathways are complex and context dependent; sometimes they are antagonistic, and sometimes they are synergistic. In this study, RNA sequencing was employed to investigate the transcriptomic changes induced by SA treatment, JA treatment and SA + JA treatment in cell suspension cultures of Andrographis paniculata, a medicinal plant with pharmacological properties; untreated cultures served as controls. Differential gene expression analysis revealed significant alterations in the transcriptomes in each treatment group. Gene Ontology enrichment analysis highlighted the modulation of biological processes related to defense response, secondary metabolism, and signal transduction. Notably, unique sets of genes were found to be differentially expressed in response to SA, JA and SA + JA, suggesting the activation of distinct signaling cascades. Furthermore, in the combination treatment, SA + JA, SA was shown to suppress the effect of JA on the overall transcriptome. A correlation of 0.932 was detected between the transcriptomes of SA-treated cells and SA + JA-treated cells. Several key transcripts associated with the enzymes involved in andrographolide biosynthesis, were both significantly overexpressed and significantly underexpressed in all the treatment groups, suggesting the need for proteomics studies for definitive validation. The findings lay the groundwork for further elucidation of mechanisms underlying defense responses against both biotrophic and necrotrophic pathogens, and hold promise for their exploitation in improving the medicinal value of A. paniculata.