Potato tonoplast sugar transporter 1 controls tuber sugar accumulation during postharvest cold storage

Cold-induced sweetening(CIS),the undesirable sugar accumulation in cold-stored potato(Solanum tuberosum L.)tubers,is a severe postharvest issue in the potato processing industry.Although the process of sucrose hydrolysis by vacuolar invertase during potato CIS is well understood,there is limited knowledge about the transportation of sucrose from the cytosol to the vacuole during postharvest cold storage.Here,we report that among the three potato tonoplast sugar transporters(TSTs),StTST1 exhibits the highest expression in tubers during postharvest cold storage.Subcellular localization analysis demonstrates that StTST1 is a tonoplast-localized protein.StTST1 knockdown decreases reducing sugar accumulation in tubers during low-temperature storage.Compared to wild-type,potato chips produced from StTST1-silenced tubers displayed significantly lower acrylamide levels and lighter color after cold storage.Transcriptome analysis manifests that suppression of StTST1 promotes starch synthesis and inhibits starch degradation in cold-stored tubers.We further establish that the increased sucrose content in the StTST1-silenced tubers might cause a decrease in the ABA content,thereby inhibiting the ABA-signaling pathway.We demonstrate that the down-regulation ofβ-amylase StBAM1 in StTST1-silenced tubers might be directly controlled by ABA-responsive element-binding proteins(AREBs).Altogether,we have shown that StTST1 plays a critical role in sugar accumulation and starchmetabolism regulation during postharvest cold storage.Thus,our findings provide a newstrategy to improve the frying quality of cold-stored tubers and reduce the acrylamide content in potato chips.

DNA methylation affects photoperiodic tuberization in potato (Solanum tuberosum L.) by mediating the expression of genes related to the photoperiod and GA pathways

Overcoming short-day-dependent tuberization to adapt to long-day conditions is critical for the widespread geographical success of potato.The genetic pathways of photoperiodic tuberization are similar to those of photoperiodic flowering.DNA methylation plays an important role in photoperiodic flowering.However,little is known about how DNA methylation affects photoperiodic tuberization in potato.Here,we verified the effect of a DNA methylation inhibitor on photoperiodic tuberization and compared the DNA methylation levels and differentially methylated genes(DMGs)in the photoperiodic tuberization process between photoperiod-sensitive and photoperiod-insensitive genotypes,aiming to dissect the role of DNA methylation in the photoperiodic tuberization of potato.We found that a DNA methylation inhibitor could promote tuber initiation in strict short-day genotypes.Whole-genome DNA methylation sequencing showed that the photoperiod-sensitive and photoperiod-insensitive genotypes had distinct DNA methylation modes in which few differentially methylated genes were shared.Transcriptome analysis confirmed that the DNA methylation inhibitor regulated the expression of the key genes involved in the photoperiod and GA pathways to promote tuber initiation in the photoperiod-sensitive genotype.Comparison of the DNA methylation levels and transcriptome levels identified 52 candidate genes regulated by DNA methylation that were predicted to be involved in photoperiodic tuberization.Our findings provide a new perspective for understanding the relationship between photoperiod-dependent and GA-regulated tuberization.Uncovering the epigenomic signatures of these pathways will greatly enhance potato breeding for adaptation to a wide range of environments.

Long-distance control of potato storage organ formation by SELF PRUNING 3D and FLOWERING LOCUS T-like 1

Plants program their meristem-associated developmental switches for timely adaptation to a changing environment.Potato(Solanum tuberosum L.)tubers differentiate from specialized belowground branches or stolons through radial expansion of their terminal ends.During this process,the stolon apex and closest axillary buds enter a dormancy state that leads to tuber eyes,which are reactivated the following spring and generate a clonally identical plant.The potato FLOWERING LOCUS T homolog SELF-PRUNING 6A(StSP6A)was previously identified as the major tuber-inducing signal that integrates day-length cues to control the storage switch.However,whether some other long-range signals also act as tuber organogenesis stimuli remains unknown.Here,we show that the florigen SELF PRUNING 3D(StSP3D)and FLOWERING LOCUS T-like 1(StFTL1)genes are activated by short days,analogously to StSP6A.Overexpression of StSP3D or StFTL1 promotes tuber formation under non-inductive long days,and the tuber-inducing activity of these proteins is graft transmissible.Using the non-tuber-bearing wild species Solanum etuberosum,a natural SP6A null mutant,we show that leaf-expressed SP6A is dispensable for StSP3D long-range activity.StSP3D and StFTL1 mediate secondary activation of StSP6A in stolon tips,leading to amplification of this tuberigen signal.StSP3D and StFTL1 were observed to bind the same protein partners as StSP6A,suggesting that they can also form transcriptionally active complexes.Together,our findings show that additional mobile tuber-inducing signals are regulated by the photoperiodic pathway.