Combined nitrogen and drought stress leads to overlapping and unique proteomic responses in potato.

MAIN CONCLUSION: Nitrogen deficient and drought-tolerant or sensitive potatoes differ in proteomic responses under combined (NWD) and individual stresses. The sensitive genotype 'Kiebitz' exhibits a higher abundance of proteases under NWD. Abiotic stresses such as N deficiency and drought affect the yield of Solanum tuberosum L. tremendously. Therefore, it is of importance to improve potato genotypes in terms of stress tolerance. In this study, we identified differentially abundant proteins (DAPs) in four starch potato genotypes under N deficiency (ND), drought stress (WD), or combined stress (NWD) in two rain-out shelter experiments. The gel-free LC-MS analysis generated a set of 1177 identified and quantified proteins. The incidence of common DAPs in tolerant and sensitive genotypes under NWD indicates general responses to this stress combination. Most of these proteins were part of the amino acid metabolism (13.9%). Three isoforms of S-adenosyl methionine synthase (SAMS) were found to be lower abundant in all genotypes. As SAMS were found upon application of single stresses as well, these proteins appear to be part of the general stress response in potato. Interestingly, the sensitive genotype 'Kiebitz' showed a higher abundance of three proteases (subtilase, carboxypeptidase, subtilase family protein) and a lower abundance of a protease inhibitor (stigma expressed protein) under NWD stress compared to control plants. The comparably tolerant genotype 'Tomba', however, displayed lower abundances of proteases. This indicates a better coping strategy for the tolerant genotype and a quicker reaction to WD when previously stressed with ND.

Proteomic analysis of two divergently responding potato genotypes (Solanum tuberosum L.) following osmotic stress treatment in vitro.

UNLABELLED: Starch potatoes (Solanum tuberosum L.) are of interest for production of starch, ethanol, and biopolymers. Due to the predicted increase in drought periods, the breeding of starch potatoes for drought tolerance is essential. This study aims to elucidate the physiological mechanisms that give rise to drought tolerance. Two genotypes contrasting in drought tolerance were compared. We applied osmotic stress which is a known component of drought stress under in vitro conditions. Shoot tips were harvested after 11days of culture on control medium and medium supplied with 0.2M sorbitol. Their proteomes were analyzed using two-dimensional isoelectric focussing sodium dodecyl sulphate polyacrylamide gel electrophoresis (2D-IEF/SDS-PAGE). Of a total of 679 distinct protein spots, 118 and 20 spots with differential abundance were found in the sensitive and the tolerant genotype, respectively, after the application of stress. Using mass spectrometry, the proteins in 100 differentially abundant spots were identified; a majority of these proteins were from the chloroplast. For the sensitive genotype, an increase in the abundance of proteinase inhibitors and their precursors, changes in stress responsive proteins and an altered RNA/DNA-binding response were observed. The differentially abundant spots of the tolerant genotype comprised one chaperone and one hydrogen peroxide detoxifying protein. BIOLOGICAL SIGNIFICANCE: Our findings reveal that the two genotypes have different responses to osmotic stress in terms of protein degradation and reactive oxygen species (ROS) scavenging and production. Our data suggest that the tolerant genotype might adjust to the applied stress more quickly. A comparative temporal analysis might provide further insights into these rapid changes and assist in the development of biomarkers.