Transcriptomic Response of In Vitro Potato ( Solanum tuberosum L.) to Piezoelectric Ultrasound

As part of a wider project to assess the impact of ultrasound on in vitro plant growth, this paper aimed to determine whether the application of piezoelectric ultrasound (PE-US) would induce changes to the transcriptome of in vitro potato (Solanum tuberosum L.). After exposing explants (single-node segments with a single leaf) to PE-US (35 kHz; 70 W) for 20 min, the effect of this stressor was determined at 0 h, 24 h, 48 h, 1 week, and 4 weeks to assess the possible immediate and residual effects of PE-US on the potato transcriptome. After mRNA was isolated, bioinformatic processing and analysis of RNA-seq datasets, KEGG analysis revealed that 24% of up-regulated biological processes were a response to stress immediately after the application of PE-US (reducing to 11% and 9% at 48 h and 4 weeks, respectively). After assessing a total of 40,430 genes for expression intensity at these five time intervals, it was found that 138, 72, 18, 5, and 59 differentially expressed genes (DEGs), respectively, were significantly up-regulated, while 6, 82, 96, 172, and 107 DEGs, respectively, were down-regulated. DEGs coding for universal stress protein, chitinase, catalase, zinc finger proteins, 21 transcription factors, glutathione S-transferase, and 17 heat shock proteins, mainly Hsp70, Hsp20, and Hsp90 proteins, and possibly the first of such discovery in US-based plant stress research, was detected. Following the validation of RNA-seq data by RT-qPCR, between SeqMonk LFC and RT-qPCR LFC, the Spearman and Pearson correlation coefficients were 0.86 and 0.90, respectively. Plantlets exposed to PE-US had significantly shorter shoots but significantly longer roots as well as higher shoot and root fresh weight, while chl b and total chl were significantly lower but the chl a/b ratio was significantly higher in plantlets exposed to PE-US. PE-US thus constituted an acute abiotic stress, but by 4 weeks, in vitro potato plantlets managed to mitigate the stress through the production of antioxidant enzyme systems and other functional metabolic changes.