*Article* **Drought-Induced Regulatory Cascades and TheirE**ff**ects on the Nutritional Quality of Developing Potato Tubers**

### **Letitia Da Ros 1,2, Raed Elferjani 3, Raju Soolanayakanahally 3,\*, Sateesh Kagale 2, Shankar Pahari 3, Manoj Kulkarni 2, Jazeem Wahab 3 and Benoit Bizimungu 4**


Received: 17 June 2020; Accepted: 28 July 2020; Published: 30 July 2020

**Abstract:** Competition for scarce water resources and the continued effects of global warming exacerbate current constraints on potato crop production. While plants' response to drought in above-ground tissues has been well documented, the regulatory cascades and subsequent nutritive changes in developing tubers have been largely unexplored. Using the commercial Canadian cultivar "Vigor", plants were subjected to a gradual drought treatment under high tunnels causing a 4 ◦C increase in the canopy temperature. Tubers were sampled for RNAseq and metabolite analysis. Approximately 2600 genes and 3898 transcripts were differentially expressed by at least 4-fold in drought-stressed potato tubers, with 75% and 69% being down-regulated, respectively. A further 229 small RNAs were implicated in gene regulation during drought. Expression of several small RNA clusters negatively correlated with expression of their six target patatin genes, suggesting involvement in the regulation of storage proteins during drought. The comparison of protein homologues between *Solanum tuberosum* L. and *Arabidopsis thaliana* L. indicated that down-regulated genes were associated with phenylpropanoid and carotenoid biosynthesis. As is indicative of reduced flow through the phenylpropanoid pathway, phenylalanine accumulated in drought-stressed tubers. This suggests that there may be nutritive implications to drought stress occurring during the potato tuber bulking phase in sensitive cultivars.

**Keywords:** crop genetics; *Solanum tuberosum*; abiotic stress; phenylpropanoids; essential amino acid; transcriptome; small RNA; comparative genomics; nutrition
