New potential roles of StDREB1 and VvWRKY2 transcription factors in potato dormancy and sprouting patterns.

In a previous study, transgenic potato plants overexpressing the StDREB1 or the VvWRKY2 transcription factor (TF) proved to have higher productivity and ameliorated tuber quality in comparison to wildtype (WT; the BF15 variety) plants. Interestingly, when stored at 4 °C, we noticed that the tubers of transgenic potato plants exhibited a delay in sprouting, hence a longer dormancy period. Therefore, we decided to study the dormancy and sprouting of these tubers (the two transgenic and the WT lines) through a physiological and biochemical characterization. WT and genetically modified (GM) tubers were stored at 4 °C for different periods (0, 30, 90, 180, and 240 days) followed by placing them in a germination chamber and the sprouting parameters were then monitored. According to our findings, the overexpression of these two TFs led to modifications in the sprouting kinetic of tubers through an extension of the dormancy period and changes in the sprouting process. Indeed, WT tubers emitted apical and lateral sprouts while those from GM plants showed mainly apical sprouts. In addition, higher reactive oxygen species (ROS) rates, indicators of tuber aging, were recorded in WT tubers compared to GM ones. The higher antioxidant enzyme activities in GM tubers seem to be responsible for aging modification in comparison to WT. The above results suggest the first report on new roles of the StDREB1 and VvWRKY2 TF which seemed to be involved in the regulation of potato tuber aging via a reduction of the main biochemical factors concentration and the ROS content leading to a longer dormancy period and a modified sprouting pattern.

Profiling beneficial phytochemicals in a potato somatic hybrid for tuber peels processing: phenolic acids and anthocyanins composition.

The purpose of this study was to characterize the peels of a CN1 somatic hybrid obtained from two dihaploid potato lines (Cardinal H14 and Nicola H1) in terms of the health-promoting phenolic compounds (phenolic acids and anthocyanins). The CN1 hybrid is defined by a pink tuber skin color making it different from the light-yellow-skinned "Spunta," which is the most commonly grown potato cultivar in Tunisia. Oven-dried peel samples derived from CN1 hybrid and cv. Spunta were ground, and phenolic compounds were extracted with water or methanol for quantification. Lyophilized peels were used for the phenolic acid and anthocyanin analyses. Higher total quantities of phenolic compounds were recovered in methanol extracts compared with water extracts. A slightly higher concentration of phenolic acids (100 mg/100 g DW) was obtained in the lyophilized peels extract of CN1 hybrid than in the cv. Spunta corresponding sample (83 mg/100 g DW). The profiles of the chlorogenic acid isomers were almost identical in both of CN1 hybrid and cv. Spunta. Caffeic acid (CA) and three caffeoylquinic acids (CQAs): 3-CQA, 4-CQA, and 5-CQA, were identified from both genotypes, 5-CQA being the dominant form in both potatoes. Since the CN1 hybrid has a pink skin color, its anthocyanin profile was also determined. The anthocyanin quantity in the CN1 peels was 5.07 mg/100 g DW, involving six different anthocyanins that were identified within the extract, namely, Pelargonidin-3-rutinoside-5-glucoside, peonidin-3-rutinoside-5-glucoside, coumaroyl ester of pelargonidin-3-rutinoside-5-glucoside, coumaroyl ester of peonidin-3-rutinoside-5-glucoside, feruloyl ester of pelargonidin-3-rutinoside-5-glucoside, and feruloyl ester of peonidin-3-rutinoside-5-glucoside. These results suggest that the peel waste of CN1 somatic hybrid can be considered as a promising source of high-value compounds for food industry.

Impact of the overexpression of the StDREB1 transcription factor on growth parameters, yields, and chemical composition of tubers from greenhouse and field grown potato plants.

Potato plants are often exposed to biotic and abiotic stresses that negatively impact their growth, development, and yield. Plants respond to different stresses by inducing large numbers of stress-responsive genes, which can be either functional or regulatory genes. Among regulatory genes, Dehydration Responsive Element Binding (DREB) genes are considered as one of the main groups of transcriptional regulators. The overexpression of these factors in several transgenic plants leads to enhancement of abiotic stress tolerance. However, a number of reports showed that the overexpression of DREB factors under control of constitutive promoter, affects their morphology and production. Therefore, it becomes interesting to evaluate the effect of the overexpression of this StDREB1 transcription factor on plant growth, morphology, yield and tuber composition under both greenhouse and field culture conditions. To our knowledge, there is no available data on the effect of DREBA-4 overexpression on potato plants morphology and yield. Indeed, most studies focused on DREB genes from A-1 and A-2 groups for other plant species. Our results showed that StDREB1, a A-4 group of DREB gene from potato (Solanum tuberosum L.), overexpressing plants did not show any growth retardation. On the contrary, they seem to be more vigorous, and produced higher tuber weight in greenhouse and field culture than the wild type (WT) plants. Moreover, the overexpression of StDREB1 transcription factor seemed to have an effect on tuber quality in terms of dry matter, starch contents and reducing sugars in comparison to the WT tubers. These data suggest that the StDREB1 gene from A-4 group of DREB subfamily can be a good candidate in potato breeding for stress tolerance.

Assessment of physiological age and antioxidant status of new somatic hybrid potato seeds during extended cold storage.

Yield components of potato are largely affected by the physiology age of the tuber seeds at planting. The current study focuses on monitoring seed tuber aging in two CN1 and CN2 somatic hybrid lines and Spunta (Sp) variety during 270 days of storage at 4 °C. Aging rate was monitored based on sprouting, emergence and tissue oxidation rates. Investigation of sprouting parameters such as physiological age index (PAI) considering physiological and chronological age and the incubation period (IP) indicated lower physiological age in hybrids than in Sp during the storage. Moreover, these analyses showed that off-seasonal growing conditions increased the aging, more clearly, in Sp tubers than in hybrid ones. However, dormancy periods (endodormancy and after storage dormancy) were equivalent in the different tuber lots. PAI and IP data when combined with those from emergence parameters (duration until emergence and stem number) seem more efficient for the characterization of the different potato lines. However, emergence indicators, when considered separately, were not able to distinguish clearly between seasonal and off-seasonal tubers. Data suggest that hybrid seeds exhibited high performances since they produced higher stem number per plant than Sp. The high aging rate in Sp tubers seems to be associated with the few developed stems. Biochemical analyses supported in part morphophysiological differences between hybrids and Sp seeds although these indicators seem more sensitive to aging. Indeed data showed that the dormancy break, and then, the development were associated with some level of tissue oxidation. Antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and carotenoids seem more enhanced after the release of dormancy. However, induction of these activities started earlier in off-seasonal tubers than in seasonal ones, this was consistent with their advanced aging level revealed by PAI and IP data. Activation of these antioxidants appears to respond effectively to the increase of ROS suggesting a better control of postharvest development and tissue deterioration especially in CN2 off-seasonal tubers. This study suggests that CN2 followed by CN1 exhibited the best performance compared to Sp variety.

The positive effect of phosphogypsum-supplemented composts on potato plant growth in the field and tuber yield.

The production of phosphoric acid from phosphate rock leads to an industrial by-product called phosphogypsum (PG). One ton of phosphoric acid generates 5 tons of PG that is frequently stocked near the production units. Several attempts were made to test PG valorization via soil amendment because of its phosphate, sulphate and calcium content. In this study, the use of PG in composting was envisaged. Composts were produced by mixing olive oil wastes and spent coffee grounds. Two concentrations of PG, 10% (A10) and 30% (A30), were tested in composting substrate in addition to control compost without PG (AT). After 8 months of fermentation, the resulting composts were used in field experiments using nine different treatments conducted to evaluate the potential use of these PG-containing composts in potato plant (cv. Spunta) cultivation. Plants were grown in the field and the different composts (AT, A10 and A30) were added as fertilizer and compared to commercial compost and cattle manure. During the culture period, a number of physiological (dry weight, chlorophyll content, tuber yield) and biochemical parameters (antioxidant activities, mineral content, starch and protein content) were followed. Similarly, chlorophyll content was measured in plants cultivated on commercial or PG supplemented composts. An increment of 55.17% in potato yield was recorded with the use of A30 the compost. Collectively, these data reveal the positive impact of the addition of PG in composting which may be adopted as a strategy for PG valorization and its use for the production of high quality edible products.