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An experiment, including potato cultivars Gloria (very early), Marfona (mid-early) and Agria (late), was carried out to assess the effects of different temperatures during two phases of the day on in vitro potato microtuber production. Temperature significantly (P <0.01) affected the percentage of cuttings that produced microtubers. The highest temperatures in either phase resulted in the lowest percentage of cuttings that produced microtubers. With lower temperature during either phase, we found more microtubers per cutting and larger microtuber sizes. The effects of temperature on individual microtuber weight were not statistically significant. However, increasing the temperature during different thermophases increased both length and weight of sprouts formed on the microtubers. Moreover, the highest temperatures resulted in the lowest levels of tuberization (as shown by bud status) and the largest sprout growth. The temperature amplitude had a significant effect as well: very large temperature amplitudes resulted in poorer tuber formation compared with smaller temperature amplitudes with the same average temperature. All three cultivars showed different responses with regard to the percentage of explants that produced microtubers. After 45 days of incubation, the percentage of explants producing microtubers, the number of microtubers and the length of the sprouts were significantly increased compared with 35 days of incubation. Nonetheless, the status of the microtubers (sprouted or not-sprouted) and the microtuber size did not change beyond 35 days of incubation. Polynomial analysis of temperature effects showed that almost all traits assessed showed a significant linear trend

Purple nutsedge ( Cyperus rotundus L.) is a globally distributed noxious weed that poses a significant challenge for control due to its fast and efficient propagation through the tuber, which is the primary reproductive organ. Gibberellic acid (GA 3 ) has proven to be crucial for tuberization in tuberous plants. Therefore, understanding the relationship between GA 3 and tuber development and propagation of C. rotundus will provide valuable information for controlling this weed. This study shows that the GA 3 content decreases with tuber development, which corresponds to lower expression of bioactive GA 3 synthesis genes ( CrGA20ox , two CrGA3ox genes) and two upregulated GA 3 catabolism genes ( CrGA2ox genes ) , indicating that GA 3 is involved in tuber development. Simultaneously, the expression of two CrDELLA genes and CrGID1 declines with tuber growth and decreased GA 3 , and yeast two-hybrid assays confirm that the GA 3 signaling is DELLA-dependent. Furthermore, exogenous application of GA 3 markedly reduces the number and the width of tubers and represses the growth of the tuber chain, further confirming the negative impact that GA 3 has on tuber development and propagation. Taken together, these results demonstrate that GA 3 is involved in tuber development and regulated by the DELLA-dependent pathway in C. rotundus and plays a negative role in tuber development and propagation.

Fluctuations in environmental conditions greatly influence life on earth. Plants, as sessile organisms, have developed molecular mechanisms to adapt their development to changes in daylength, or photoperiod. One of the first plant features that comes to mind as affected by the duration of the day is flowering time; we all bring up a clear image of spring blossom. However, for many plants flowering happens at other times of the year, and many other developmental aspects are also affected by changes in daylength, which range from hypocotyl elongation in Arabidopsis thaliana to tuberization in potato or autumn growth cessation in trees. Strikingly, many of the processes affected by photoperiod employ similar gene networks to respond to changes in the length of light/dark cycles. In this review, we have focused on developmental processes affected by photoperiod that share similar genes and gene regulatory networks.

For many potato cultivars, tuber yield is optimal at average daytime temperatures in the range 14–22 °C. Above this range, tuber yield is reduced for most cultivars. We previously reported that moderately elevated temperature increases steady-state expression of the core circadian clock gene TIMING OF CAB EXPRESSION 1 (StTOC1) in developing tubers, whereas expression of the StSP6A tuberization signal is reduced, along with tuber yield. In this study we provide evidence that StTOC1 links environmental signalling with potato tuberization by suppressing StSP6A autoactivation in the stolons. We show that transgenic lines silenced in StTOC1 expression exhibit enhanced StSP6A transcript levels and changes in gene expression in developing tubers that are indicative of an elevated sink strength. Nodal cuttings of StTOC1 antisense lines displayed increased tuber yields at moderately elevated temperatures, whereas tuber yield and StSP6A expression were reduced in StTOC1 overexpressor lines. Here we identify a number of StTOC1 binding partners and demonstrate that suppression of StSP6A expression is independent of StTOC1 complex formation with the potato homolog StPIF3. Down-regulation of StTOC1 thus provides a strategy to mitigate the effects of elevated temperature on tuber yield.

Various transcriptional networks and plant hormones have been implicated in controlling different aspects of potato tuber formation. Due to its broad impact on many plant developmental processes, a role for auxin in tuber initiation has been suggested but never fully resolved. Here, auxin concentrations were measured throughout the plant prior to and during the process of tuber formation. Auxin levels increase dramatically in the stolon prior to tuberization and remain relatively high during subsequent tuber growth, suggesting a promoting role for auxin in tuber formation. Furthermore, in vitro tuberization experiments showed higher levels of tuber formation from axillary buds of explants where the auxin source (stolon tip) had been removed. This phenotype could be rescued by application of auxin on the ablated stolon tips. In addition, a synthetic strigolactone analogue applied on the basal part of the stolon resulted in fewer tubers. The experiments indicate that a system for the production and directional transport of auxin exists in stolons and acts synergistically with strigolactones to control the outgrowth of the axillary stolon buds, similar to the control of above-ground shoot branching.

Potato (Solanum tuberosum L.) can reproduce sexually through flowering and asexually through tuberization. While tuberization has been thoroughly studied, little research has been done on potato flowering. Flower bud development in the strictly short-day tuberizing S. tuberosum group Andigena is impaired under short-day conditions. This impaired development may indicate that tuberization negatively influences flowering. Here, we determine how tuberization affects flower bud development. To find out whether the absence of tubers improves flowering, we prevented tuberization by: (i) grafting potato scions onto wild potato rootstocks, which were unable to form tubers; (ii) removing stolons, the underground structures on which tubers form; and (iii) using plants that were silenced in the tuberization signal StSP6A. Additionally, transgenic plants with increased StSP6A expression were used to determine if flower bud development was impaired. The absence of a tuber sink alone did not accelerate flower bud development, nor did it allow more plants to reach anthesis (open flowering stage) or have more open flowers. Interestingly, reducing StSP6A expression improved flower bud development, and increasing expression impaired it. Our results show that flower bud development in potato is repressed by the tuberization signal StSP6A, and not by competition with the underground tuber sink.

The study of the effects of auxins on potato tuberization corresponds to one of the oldest experimental systems in plant biology, which has remained relevant for over 70 years. However, only recently, in the postgenomic era, the role of auxin in tuber formation and other vital processes in potatoes has begun to emerge. This review describes the main results obtained over the entire period of auxin-potato research, including the effects of exogenous auxin; the content and dynamics of endogenous auxins; the effects of manipulating endogenous auxin content; the molecular mechanisms of auxin signaling, transport and inactivation; the role and position of auxin among other tuberigenic factors; the effects of auxin on tuber dormancy; the prospects for auxin use in potato biotechnology. Special attention is paid to recent insights into auxin function in potato tuberization and stress resistance. Taken together, the data discussed here leave no doubt on the important role of auxin in potato tuberization, particularly in the processes of tuber initiation, growth and sprouting. A new integrative model for the stage-dependent auxin action on tuberization is presented. In addition, auxin is shown to differentially affects the potato resistance to biotrophic and necrotrophic biopathogens. Thus, the modern auxin biology opens up new perspectives for further biotechnological improvement of potato crops.

A genetic study of natural variation in potato tuberization onset, an important phenotype for breeding potatoes adapted to different global day lengths, has revealed a role for StCDF1 , a member of the DOF family of transcription factors. Potatoes take northerly route Potatoes were introduced into Europe from the Andes in the sixteenth century. In South America the plants had adapted to form tubers under short-day conditions, so one of the first traits likely to have been selected by growers would have been for tuber production in the long days of spring and summer encountered in northern latitudes. Christian Bachem and colleagues have cloned the gene responsible for early tuberization under long-day conditions. It encodes a DOF transcription factor that acts as a mediator between the circadian clock and the StSP6A tuberization signal. The natural allelic variation of this protein is sufficient for it to have been the basis of the domestication of the potato in latitudes where there is large summer/winter day-length variation. Breeding programmes selecting for further variants could take potatoes into new geographic regions. Potato ( Solanum tuberosum L.) originates from the Andes and evolved short-day-dependent tuber formation as a vegetative propagation strategy. Here we describe the identification of a central regulator underlying a major-effect quantitative trait locus for plant maturity and initiation of tuber development. We show that this gene belongs to the family of DOF (DNA-binding with one finger) transcription factors 1 and regulates tuberization and plant life cycle length, by acting as a mediator between the circadian clock and the StSP6A mobile tuberization signal 2 . We also show that natural allelic variants evade post-translational light regulation, allowing cultivation outside the geographical centre of origin of potato. Potato is a member of the Solanaceae family and is one of the world’s most important food crops. This annual plant originates from the Andean regions of South America 3 . Potato develops tubers from underground stems called stolons. Its equatorial origin makes potato essentially short-day dependent for tuberization and potato will not make tubers in the long-day conditions of spring and summer in the northern latitudes. When introduced in temperate zones, wild material will form tubers in the course of the autumnal shortening of day-length. Thus, one of the first selected traits in potato leading to a European potato type 4 is likely to have been long-day acclimation for tuberization. Potato breeders can exploit the naturally occurring variation in tuberization onset and life cycle length, allowing varietal breeding for different latitudes, harvest times and markets.

The effect of melatonin (MT) on potato plants under drought stress is still unclear in the available literature. Here, we studied the effect of MT as a foliar application at 0, 0.05, 0.1, and 0.2 mM on potato plants grown under well-watered and drought stressed conditions during the most critical period of early tuberization stage. The results indicated that under drought stress conditions, exogenous MT significantly (p ≤ 0.05) improved shoot fresh weight, shoot dry weight, chlorophyll (Chl; a, b and a + b), leaf relative water content (RWC), free amino acids (FAA), non-reducing sugars, total soluble sugars, cell membrane stability index, superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX) compared to the untreated plants. Meanwhile, carotenoids, proline, methylglyoxal (MG), H2O2, lipid peroxidation (malondialdehyde; MDA) and abscisic acid (ABA) were significantly decreased compared to the untreated plants. These responses may reveal the protective role of MT against drought induced carbonyl/oxidative stress and enhancing the antioxidative defense systems. Furthermore, tuber yield was differentially responded to MT treatments under well-watered and drought stressed conditions. Since, applied-MT led to an obvious decrease in tuber yield under well-watered conditions. In contrast, under drought conditions, tuber yield was substantially increased by MT-treatments up to 0.1 mM. These results may imply that under water deficiency, MT can regulate the tuberization process in potato plants by hindering ABA transport from the root to shoot system, on the one hand, and by increasing the non-reducing sugars on the other hand.