Transcriptomic analysis of seed germination improvement of Andrographis paniculata responding to air plasma treatment

Abstract

The plasma seed treatment is effective for promoting seed germination in many crops. However, the biological mechanism remains unclear. Therefore, mRNA sequencing was used to screen differentially expressed genes in the germination process of Andrographis paniculata seeds treated with air plasma (power density = 8.99 J/cm 3 ). Following plasma treatment, the germination percentages were significantly higher than those of the control, they were 3.5±0.6% vs . 0 at 28 hours after sowing (HAS) and 50.3±2.6% vs . 37.3±1.7% at 48 HAS. After unigenes were assembled and annotated, 125 differentially expressed genes (DEGs) were detected at 28 HAS, compared with nine DEGs at 48 HAS, but no DEGs were detected at 0 HAS, indicating that air plasma treatment mainly changed the gene expression of A . paniculata seeds at 28 HAS. The NCED5 expression level of the treated group was less than one-fifth of the control, and the expressions of three ethylene response factors were significantly higher than the control at 28 HAS, indicating that lower abscisic acid levels play an important role and ethylene signal transduction also participates in radicle protrusion. ACO , NRT1 and PRP3 expressions were significantly higher than in the control at 48 HAS, suggesting that higher ethylene levels cause the endosperm cap to weaken and start to grow root hairs and lateral roots earlier. These findings reveal that plasma promotes seed germination mainly by regulating the expression of hormone-related genes. And the possible signal transduction of related hormones was discussed.

RNA Sequencing of Arabidopsis thaliana Seedlings after Non-Thermal Plasma-Seed Treatment Reveals Upregulation in Plant Stress and Defense Pathways

“…Three studies, including ours, show a similar general pattern of predominantly downregulated genes [ 26 , 28 ]. However, this is not the case for other studies [ 25 , 27 ]. These differences may be due to physiological differences between different organisms but also to the plasma conditions or the selected RNA-seq approach.…”

“…The aim of our study was to look at the long-term memory effect of the plasma treatment by using 6-day-old seedlings rather than 1–2-day-old seeds because both the root and stem would have emerged from the seed, and this would ensure that there would be transcriptional changes that could be absent if the extraction is performed too soon; this was the case in the Andrographis study [ 25 ]. Moreover, it is common practice to use young seedlings because they are more sensitive to stress, and therefore, it would be possible to observe acute stress.…”

“…Based on our gene enrichment analysis in Figure 7 A,C,D, our main findings were an increased defense response, specifically of the glucosinolate pathway with an 80 s plasma treatment time several days after observing accelerated germination. The production of secondary metabolites involved in plant defense has been reported previously as well as changes in glutathione, an antioxidant involved in detoxification, particularly of reactive oxygen and nitrogen species during stress in living organisms [ 25 , 26 , 28 ]. Our data in Figure 5 , Figure 6 , Figure 7 and Figure 8 suggest that the plant may still be responding to the stress even 6 days after the initial treatment where a continuous cascade of programs has been triggered, which affects both primary and secondary metabolisms.…”

“…To verify whether our interpretations are valid, the most relevant comparison can be made with the results available in another study using A. thaliana and, where appropriate, other transcriptomic studies [ 25 , 26 , 27 , 28 ]. A detailed comparison between our experimental setup and that of Cui and co-authors is shown in Table S3 .…”

“…Although the plant choice is well justified based on local or global economic importance, there is often only one or a few studies of each plant type, which makes it difficult to compare the results and find commonalities. However, there are a few studies published recently using transcriptomics that provide a global overview of changes in gene expression after plasma treatment [ 25 , 26 , 27 , 28 ].…”