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.Key Message Piezoelectric ultrasound (PE-US) constitutes a nonfatal abiotic stress to in vitro potato. A notable discovery was the expression of 17 heat shock proteins in response to this abiotic stress.Electronic supplementary material The online version of this article (https://doi.

Main conclusion Studies on the tissue culture of apple have allowed for molecular, biotechnological and applied breeding research to advance. In the past 8 years, over 100 papers advancing basic biology, genetic transformation and cryobiology have emerged. Apple (Malus × domestica Borkh.; Rosaceae) is an important fruit crop grown mainly in temperate regions of the world. In vitro tissue culture is a biotechnological technique that has been used to genetically improve cultivars (scions) and rootstocks. This updated review presents a synthesis of findings related to the tissue culture of apple and other Malus spp. between 2010 and 2018. Increasingly complex molecular studies that are examining the apple genome, for example, in a bid to identify the cause of epigenetic mutations and the role of transposable elements in this process would benefit from genetically stable source material, which can be produced in vitro. Several notable or curious in vitro culture methods have been reported to improve shoot regeneration and induce the production of tetraploids in apple cultivars and rootstocks. Existing studies have revealed the molecular mechanism underlying the inhibition of adventitious roots by cytokinin. The use of the plant growth correction factor allows hypothetical shoot production from leaf-derived thin cell layers relative to conventional leaf explants to be determined. This updated review will allow novices and established researchers to advance apple and Malus biotechnology and breeding programs.

Key message In response to an ultrasound pulse, several hundred DEGs, including in response to stress, were up- or down-regulated in in vitro potato plantlets. Despite this abiotic stress, plantlets survived. Abstract Ultrasound (US) can influence plant growth and development. To better understand the genetic mechanism underlying the physiological response of potato to US, single-node segments of four-week-old in vitro plantlets were subjected to US at 35 kHz for 20 min. Following mRNA purification, 10 cDNA libraries were assessed by RNA-seq. Significantly differentially expressed genes (DEGs) were categorized by gene ontology or Kyoto Encyclopedia of Genes and Genomes identifiers. The expression intensity of 40,430 genes was studied. Several hundred DEGs associated with biosynthesis, carbohydrate metabolism and catabolism, cellular protein modification, and response to stress, and which were expressed mainly in the extracellular region, nucleus, and plasma membrane, were either up- or down-regulated in response to US. RT-qPCR was used to validate RNA-seq data of 10 highly up- or down-regulated DEGs, and both Spearman and Pearson correlations between SeqMonk LFC and RT-qPCR LFC were highly positive (0.97). This study examines how some processes evolved over time (0 h, 24 h, 48 h, 1 week and 4 weeks) after an abiotic stress (US) was imposed on in vitro potato explants, and provides clues to the temporal dynamics in DEG-based enzyme functions in response to this stress. Despite this abiotic stress, plantlets survived. Electronic supplementary material The online version of this article (10.1007/s11103-019-00876-0) contains supplementary material, which is available to authorized users.