Drought stress is a major threat to sustainable crop production worldwide. Despite the positive role of calcium (Ca²⁺) in improving plant drought tolerance in different crops, little attention has been paid to its role in mitigating drought stress in potatoes. In the present study, we studied the effect of foliar chelated sugar alcohol calcium treatments on two potato cultivars with different drought responses applied 15 and 30 days after limiting soil moisture. The results showed that the foliar application of calcium treatments alleviated the SPAD chlorophyll loss of the drought-sensitive cultivar ‘Atlantic’ (Atl) and reduced the inhibition of photosynthetic parameters, leaf anatomy deformation, and MDA and H₂O₂ content of both cultivars under drought stress. The Ca²⁺ treatments changed the expression of several Calcium-Dependent Protein Kinase (StCDPK) genes involved in calcium sensing and signaling and significantly increased antioxidant enzyme activities, average tuber weight per plant, and tuber quality of both cultivars. We conclude that calcium spray treatments improved the drought tolerance of both potato cultivars and were especially effective for the drought-sensitive cultivar. The present work suggests that the foliar application of calcium is a promising strategy to improve commercial potato yields and the economic efficiency of potato production under drought stress conditions.

Calcium-dependent protein kinases (CDPKs), which are activated by transient changes in the Ca²⁺ concentration in plants, are important for various biological processes, such as growth, development, defense against biotic and abiotic stresses, and others. Mannitol is commonly used as an osmotic regulatory substance in culture medium or nutrient solutions to create water-deficit conditions. Here, we cloned the potato (Solanum tuberosum L.) StCDPK13 gene and generated stable transgenic StCDPK13-overexpression potato plants. To investigate the potential functions of StCDPK13 in response to drought stress, overexpression-transgenic (OE1, OE2, and OE7) and wild-type (WT) potato seedlings were cultured on MS solid media without or with mannitol, representing the control or drought stress, for 20 days; the elevated mannitol concentrations (150 and 200 mM) were the drought stress conditions. The StCDPK13 gene was consistently expressed in different tissues and was induced by drought stress in both OE and WT plants. The phenotypic traits and an analysis of physiological indicators revealed that the transgenic plants exhibited more tolerance to drought stress than the WT plants. The overexpression lines showed an increased plant height, number of leaves, dry shoot weight, root length, root number, root volume, number of root tips, fresh root weight, and dry root weight under drought stress. In addition, the activities of antioxidant enzymes (CAT, SOD, and POD) and the accumulation of proline and neutral sugars were significantly increased, whereas the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂) and O₂^•−, were significantly reduced in the OE lines compared to WT plants under drought stress. Moreover, the stomatal aperture of the leaves and the water loss rate in the leaves of the OE lines were significantly reduced under drought stress compared to the WT plants. In addition, the overexpression of StCDPK13 upregulated the expression levels of stress-related genes under drought stress. Collectively, these results indicate that the StCDPK13 gene plays a positive role in drought tolerance by reducing the stomatal aperture, promoting ROS scavenging, and alleviating oxidative damage under drought stress in potatoes.

Sucrose non-ferment 1-related protein kinase 2 (SnRK2) is a highly conserved protein kinase in plants that plays an important role in regulating plant response to drought stress. Although it has been reported in some plants, the evolutionary relationship of potato SnRK2s and their function in drought resistance have not been systematically analyzed. In this study, molecular characteristic analysis showed that 8 StSnRK2s were distributed on six chromosomes, coding proteins were divided into three subgroups, and StSnRK2s clustered in the same subgroup had similar conserved motifs and domains. In addition, StSnRK2 has a wide range of replication events in some species, making it closer to dicots in the process of evolution. In addition, the average nonsynonymous substitution rate/synonymous substitution rate (Ka/Ks) value of SnRK2s in monocots was higher than that of dicots. The codon usage index showed that SnRK2s prefer to use cytosine 3 (C3s), guanine 3 (G3s) and GC content (GC3s) in monocots, whereas thymine 3 (T3s) and adenine 3 (A3s) are preferred in dicots. Furthermore, stress response analysis showed that the expression of StSnRK2s under different degrees of drought stress significantly correlated with one or more stress-related physiological indices, such as proline and malondialdehyde (MDA) content, superoxide dismutase (SOD) and catalase (CAT) activity, ion leakage (IL) etc. The drought resistance of StSnRK2 transgenic plants was determined to occur in the order of StSnRK2.1/2.8 > StSnRK2.2/2.5 > StSnRK2.4/2.6 > StSnRK2.3 > StSnRK2.7, was attributed to not only lower IL but also higher proline, soluble sugar contents and stress-related genes in transgenic plants compared to wild type (WT). In conclusion, this study provides useful insights into the evolution and function of StSnRK2s and lays a foundation for further study on the molecular mechanism of StSnRK2s regulating potato drought resistance.

The study was conducted with C31 and C80 genotypes of the potato (Solanum tuberosum L.), which are tolerant and susceptible to phosphite (Phi, H₂PO₃), respectively. To decipher the molecular mechanisms underlying tolerance and susceptibility to Phi in the potato, RNA sequencing was used to study the global transcriptional patterns of the two genotypes. Media were prepared with 0.25 and 0.50 mM Phi, No-phosphorus (P), and 1.25 mM (phosphate, Pi as control). The values of fragments per kilobase of exon per million mapped fragments of the samples were also subjected to a principal component analysis, grouping the biological replicates of each sample. Using stringent criteria, a minimum of 819 differential (DEGs) were detected in both C80-Phi-0.25_vs_C80-Phi-0.50 (comprising 517 upregulated and 302 downregulated) and C80-Phi-0.50_vs_C80-Phi-0.25 (comprising 302 upregulated and 517 downregulated) and a maximum of 5214 DEGs in both C31-Con_vs_C31-Phi-0.25 (comprising 1947 upregulated and 3267 downregulated) and C31-Phi-0.25_vs_C31-Con (comprising 3267 upregulated and 1947 downregulated). DEGs related to the ribosome, plant hormone signal transduction, photosynthesis, and plant–pathogen interaction performed important functions under Phi stress, as shown by the Kyoto Encyclopedia of Genes and Genomes annotation. The expressions of transcription factors increased significantly in C31 compared with C80. For example, the expressions of Soltu.DM.01G047240, Soltu.DM.08G015900, Soltu.DM.06G012130, and Soltu.DM.08G012710 increased under P deficiency conditions (Phi-0.25, Phi-0.50, and No-P) relative to the control (P sufficiency) in C31. This study adds to the growing body of transcriptome data on Phi stress and provides important clues to the Phi tolerance response of the C31 genotype.