Molecular Insights into the Accelerated Sprouting of and Apical Dominance Release in Potato Tubers Subjected to Post-Harvest Heat Stress.

Climate change-induced heat stress (HS) increasingly threatens potato (Solanum tuberosum L.) production by impacting tuberization and causing the premature sprouting of tubers grown during the hot season. However, the effects of post-harvest HS on tuber sprouting have yet to be explored. This study aims to investigate the effects of post-harvest HS on tuber sprouting and to explore the underlying transcriptomic changes in apical bud meristems. The results show that post-harvest HS facilitates potato tuber sprouting and negates apical dominance. A meticulous transcriptomic profiling of apical bud meristems unearthed a spectrum of differentially expressed genes (DEGs) activated in response to HS. During the heightened sprouting activity that occurred at 15-18 days of HS, the pathways associated with starch metabolism, photomorphogenesis, and circadian rhythm were predominantly suppressed, while those governing chromosome organization, steroid biosynthesis, and transcription factors were markedly enhanced. The critical DEGs encompassed the enzymes pivotal for starch metabolism, the genes central to gibberellin and brassinosteroid biosynthesis, and influential developmental transcription factors, such as SHORT VEGETATIVE PHASE, ASYMMETRIC LEAVES 1, SHOOT MERISTEMLESS, and MONOPTEROS. These findings suggest that HS orchestrates tuber sprouting through nuanced alterations in gene expression within the meristematic tissues, specifically influencing chromatin organization, hormonal biosynthesis pathways, and the transcription factors presiding over meristem fate determination. The present study provides novel insights into the intricate molecular mechanisms whereby post-harvest HS influences tuber sprouting. The findings have important implications for developing strategies to mitigate HS-induced tuber sprouting in the context of climate change.

ScAREB4 promotes potato constitutive and acclimated freezing tolerance associated with enhancing trehalose synthesis and oxidative stress tolerance.

Cold is a major environmental factor that restrains potato production. Abscisic acid (ABA) can enhance freezing tolerance in many plant species, but powerful evidence of the ABA-mediated signalling pathway related to freezing tolerance is still in deficiency. In the present study, cold acclimation capacity of the potato genotypes was enhanced alongside with improved endogenous content of ABA. Further exogenous application of ABA and its inhibitor (NDGA) could enhance and reduce potato freezing tolerance, respectively. Moreover, expression pattern of downstream genes in ABA signalling pathway was analysed and only ScAREB4 was identified with specifically upregulate in S. commersonii (CMM5) after cold and ABA treatments. Transgenic assay with overexpression of ScAREB4 showed that ScAREB4 promoted freezing tolerance. Global transcriptome profiling indicated that overexpression of ScAREB4 induced expression of TPS9 (trehalose-6-phosphate synthase) and GSTU8 (glutathione transferase), in accordance with improved TPS activity, trehalose content, higher GST activity and accumulated dramatically less H2 O2 in the ScAREB4 overexpressed transgenic lines. Taken together, the current results indicate that increased endogenous content of ABA is related to freezing tolerance in potato. Moreover, ScAREB4 functions as a downstream transcription factor of ABA signalling to promote cold tolerance, which is associated with increased trehalose content and antioxidant capacity.

StMLP1, as a Kunitz trypsin inhibitor, enhances potato resistance and specifically expresses in vascular bundles during Ralstonia solanacearum infection.

Miraculin-like proteins (MLPs), members of the Kunitz trypsin inhibitor (KTI) family that are present in various plants, have been discovered to have a role in defending plants against pathogens. In this study, we identified a gene StMLP1 in potato that belongs to the KTI family. We found that the expression of StMLP1 gradually increases during Ralstonia solanacearum (R. solanacearum) infection. We characterized the promoter of StMLP1 as an inducible promoter that can be triggered by R. solanacearum and as a tissue-specific promoter with specificity for vascular bundle expression. Our findings demonstrate that StMLP1 exhibits trypsin inhibitor activity, and that its signal peptide is essential for proper localization and function. Overexpression of StMLP1 in potato can enhance the resistance to R. solanacearum. Inhibiting the expression of StMLP1 during infection accelerated the infection by R. solanacearum to a certain extent. In addition, the RNA-seq results of the overexpression-StMLP1 lines indicated that StMLP1 was involved in potato immunity. All these findings in our study reveal that StMLP1 functions as a positive regulator that is induced and specifically expressed in vascular bundles in response to R. solanacearum infection.

StHAB1, a negative regulatory factor in abscisic acid signaling, plays crucial roles in potato drought tolerance and shoot branching.

Abscisic acid (ABA) is critical in drought tolerance and plant growth. Group A protein type 2C phosphatases (PP2Cs) are negative regulators of ABA signaling and plant adaptation to stress. Knowledge about the functions of potato group A PP2Cs is limited. Here, we report that the potato group A PP2C StHAB1 is broadly expressed in potato plants and strongly induced by ABA and drought. Suppression of StHAB1 enhanced potato ABA sensitivity and drought tolerance, whereas overexpression of the dominant mutant StHAB1G276D compromised ABA sensitivity and drought tolerance. StHAB1 interacts with almost all ABA receptors and the Snf1-Related Kinase OST1. Suppressing StHAB1 and overexpressing StHAB1G276D alter potato growth morphology; notably, overexpression of StHAB1G276D causes excessive shoot branching. RNA-sequencing analyses identified that the auxin efflux carrier genes StPIN3, StPIN5, and StPIN8 were up-regulated in StHAB1G276D-overexpressing axillary buds. Correspondingly, the auxin concentration was reduced in StHAB1G276D-overexpressing axillary buds, consistent with the role of auxin in repressing lateral branch outgrowth. The expression of BRANCHED1s (StBRC1a and StBRC1b) was unchanged in StHAB1G276D-overexpressing axillary buds, suggesting that StHAB1G276D overexpression does not cause axillary bud outgrowth via regulation of BRC1 expression. Our findings demonstrate that StHAB1 is vital in potato drought tolerance and shoot branching.

Genome sequence analysis provides insights into the mode of 2n egg formation in Solanum malmeanum.

KEY MESSAGE: Our genomic investigation confirms the mechanism of 2n eggs formation in S. malmeanum and aid in optimizing the use of wild germplasm. Wild potatoes are a valuable source of agronomic traits. However, substantial reproductive barriers limit gene flow into cultivated species. 2n gametes are instrumental in preventing endosperm abortion caused by genetic imbalances in the endosperm. However, little is known about the molecular mechanisms underlying the formation of 2n gametes. Here, the wild species Solanum malmeanum Bitter (2x, 1EBN, endosperm balance number) was used in inter- and intrapoloid crosses with other Solanum species, with viable seeds being produced only when S. malmeanum was used as the female parent to cross the 2EBN Solanum genus and with the likely involvement of 2n gametes. Subsequently, we substantiated the formation of 2n eggs in S. malmeanum using fluorescence in situ hybridization (FISH) and genomic sequencing technology. Additionally, the transmission rate of maternal heterozygous polymorphism sites was assessed from a genomic perspective to analyze the mode of 2n egg formation in S. malmeanum × S. tuberosum and S. malmeanum × S. chacoense crosses; each cross acquired an average of 31.12% and 22.79% maternal sites, respectively. This confirmed that 2n egg formation in S. malmeanum attributed to second-division restitution (SDR) coupled with the occurrence of exchange events. The high-throughput sequencing technology used in this study has strong advantages over traditional cytological analyses. Furthermore, S. malmeanum, which has a variety of excellent traits not available from present cultivated potato genepool, has received little research attention and has successfully achieved gene flow in cultivated species in the current study. These findings will facilitate the understanding and optimization of wild germplasm utilization in potatoes.

Molecular Marker-Assisted Selection for Frost Tolerance in a Diallel Population of Potato.

A multi-parental population is an innovative tool for mapping large numbers of loci and genetic modifications, particularly where they have been used for breeding and pre-breeding in crops. Frost injury is an environmental stress factor that greatly affects the growth, development, production efficiency, and geographical distribution of crops. No reported study has focused on genetic mapping and molecular marker development using diallel populations of potatoes. In this study, 23 successful cross combinations, obtained by a half diallel cross among 16 parents, including eight frost-tolerant advanced breeding lines and eight cultivars, were used to map the genetic loci for frost tolerance and to create a molecular marker-assisted selection (MAS) system. Three candidate regions related to frost tolerance on chromosomes II, V, and IX were mapped by bulked segregant analysis (BSA). Furthermore, six SNP markers associated with frost tolerance from candidate regions were developed and validated. Above all, a MAS system for the frost tolerance screening of early breeding offspring was established. This study highlights the practical advantages of applying diallel populations to broaden and improve frost-tolerant germplasm resources.

A novel effector RipBT contributes to Ralstonia solanacearum virulence on potato.

Ralstonia solanacearum is one of the most destructive plant-pathogenic bacteria, infecting more than 200 plant species, including potato (Solanum tuberosum) and many other solanaceous crops. R. solanacearum has numerous pathogenicity factors, and type III effectors secreted through type III secretion system (T3SS) are key factors to counteract host immunity. Here, we show that RipBT is a novel T3SS-secreted effector by using a cyaA reporter system. Transient expression of RipBT in Nicotiania benthamiana induced strong cell death in a plasma membrane-localization dependent manner. Notably, mutation of RipBT in R. solanacearum showed attenuated virulence on potato, while RipBT transgenic potato plants exhibited enhanced susceptibility to R. solanacearum. Interestingly, transcriptomic analyses suggest that RipBT may interfere with plant reactive oxygen species (ROS) metabolism during the R. solanacearum infection of potato roots. In addition, the expression of RipBT remarkably suppressed the flg22-induced pathogen-associated molecular pattern-triggered immunity responses, such as the ROS burst. Taken together, RipBT acts as a T3SS effector, promoting R. solanacearum infection on potato and presumably disturbing ROS homeostasis.

A Phytophthora infestans RXLR effector AVR8 suppresses plant immunity by targeting a desumoylating isopeptidase DeSI2.

The potato's most devastating disease is late blight, which is caused by Phytophthora infestans. Whereas various resistance (R) genes are known, most are typically defeated by this fast-evolving oomycete pathogen. However, the broad-spectrum and durable R8 is a vital gene resource for potato resistance breeding. To support an educated deployment of R8, we embarked on a study on the corresponding avirulence gene Avr8. We overexpressed Avr8 by transient and stable transformation, and found that Avr8 promotes colonization of P. infestans in Nicotiana benthamiana and potato, respectively. A yeast-two-hybrid (Y2H) screen showed that AVR8 interacts with a desumoylating isopeptidase (StDeSI2) of potato. We overexpressed DeSI2 and found that DeSI2 positively regulates resistance to P. infestans, while silencing StDeSI2 downregulated the expression of a set of defense-related genes. By using a specific proteasome inhibitor, we found that AVR8 destabilized StDeSI2 through the 26S proteasome and attenuated early PTI responses. Altogether, these results indicate that AVR8 manipulates desumoylation, which is a new strategy that adds to the plethora of mechanisms that Phytophthora exploits to modulate host immunity, and StDeSI2 provides a new target for durable resistance breeding against P. infestans in potato.

Protein phosphatase StTOPP6 negatively regulates potato bacterial wilt resistance by modulating MAPK signaling.

Potato (Solanum tuberosum) is an important crop globally and is grown across many regions in China, where it ranks fourth in the list of staple foods. However, its production and quality are severely affected by bacterial wilt caused by Ralstonia solanacearum. In this study, we identified StTOPP6, which belongs to the type one protein phosphatase (TOPP) family, and found that transient knock down of StTOPP6 in potato increased resistance against R. solanacearum. RNA-seq analysis showed that knock down of StTOPP6 activated immune responses, and this defense activation partly depended on the mitogen-activated protein kinase (MAPK) signal pathway. StTOPP6 inhibited the expression of StMAPK3, while overexpression of StMAPK3 enhanced resistance to R. solanacearum, supporting the negative role of StTOPP6 in plant immunity. Consistent with the results of knock down of StTOPP6, overexpressing the phosphatase-dead mutation StTOPP6m also attenuated infection and up-regulated MAPK3, showing that StTOPP6 activity is required for disease. Furthermore, we found that StTOPP6 affected the StMAPK3-mediated downstream defense pathway, eventually suppressing the accumulation of reactive oxygen species (ROS). Consistent with these findings, plants with knock down of StTOPP6, overexpression of StTOPP6m, and overexpression of StMAPK3 all displayed ROS accumulation and enhanced resistance to R. solanacearum. Taken together, the findings of our study demonstrate that StTOPP6 negatively regulates resistance to bacterial wilt by affecting the MAPK3-mediated pathway.

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.

Suppression of the tonoplast sugar transporter, StTST3.1, affects transitory starch turnover and plant growth in potato.

Transitory starch and vacuolar sugars function as highly dynamic pools of instantly accessible metabolites in plant leaf cells. Their metabolic regulation is critical for plant survival. The tonoplast sugar transporters (TSTs), responsible for sugar uptake into vacuoles, regulate cellular sugar partitioning and vacuolar sugar accumulation. However, whether TSTs are involved in leaf transient starch turnover and plant growth is unclear. Here, we found that suppressing StTST3.1 resulted in growth retardation and pale green leaves in potato plants. StTST3.1-silenced plants displayed abnormal chloroplasts and impaired photosynthetic performance. The subcellular localization assay and the oscillation expression patterns revealed that StTST3.1 encoded a tonoplast-localized protein and responded to photoperiod. Moreover, RNA-seq analyses identified that starch synthase (SS2 and SS6) and glucan water, dikinase (GWD), were downregulated in StTST3.1-silenced lines. Correspondingly, the capacity for starch synthesis and degradation was decreased in StTST3.1-silenced lines. Surprisingly, StTST3.1-silenced leaves accumulated exceptionally high levels of maltose but low levels of sucrose and hexose. Additionally, chlorophyll content was reduced in StTST3.1-silenced leaves. Analysis of chlorophyll metabolic pathways found that Non-Yellow Coloring 1 (NYC1)-like (NOL), encoding a chloroplast-localized key enzyme that catalyzes the initial step of chlorophyll b degradation, was upregulated in StTST3.1-silenced leaves. Transient overexpression of StNOL accelerated chlorophyll b degradation in tobacco leaves. Our results indicated that StTST3.1 is involved in transitory starch turnover and chlorophyll metabolism, thereby playing a critical role in normal potato plant growth.

Leaves and stolons transcriptomic analysis provide insight into the role of phytochrome F in potato flowering and tuberization.

Photoperiod plays a critical role in controlling the formation of sexual or vegetative reproductive organs in potato. Although StPHYF-silenced plants overcome day-length limitations to tuberize through a systemic effect on tuberigen StSP6A expression in the stolon, the comprehensive regulatory network of StPHYF remains obscure. Therefore, the present study investigated the transcriptomes of StPHYF-silenced plants and observed that, in addition to known components of the photoperiodic tuberization pathway, florigen StSP3D and other flowering-related genes were activated in StPHYF-silenced plants, exhibiting an early flowering response. Additionally, grafting experiments uncovered the long-distance effect of StPHYF silencing on gene expression in the stolon, including the circadian clock components, flowering-associated MADSs, and tuberization-related regulatory genes. Similar to the AtFT-AtAP1 regulatory module in Arabidopsis, the present study established that the AP1-like StMADS1 functions downstream of the tuberigen activation complex (TAC) and that suppressing StMADS1 inhibits tuberization in vitro and delays tuberization in vivo. Moreover, the expression of StSP6A was downregulated in StMADS1-silenced plants, implying the expression of StSP6A may be feedback-regulated by StMADS1. Overall, these results reveal that the regulatory network of StPHYF controls flowering and tuberization and targets the crucial tuberization factor StMADS1 through TAC, thereby providing a better understanding of StPHYF-mediated day-length perception during potato reproduction.

Comparative transcriptomics analysis reveals a calcineurin B-like gene to positively regulate constitutive and acclimated freezing tolerance in potato.

Freezing stress is a major limiting factor in crop production. To increase frost-hardiness of crops via breeding, deciphering the genes conferring freezing-tolerance is vital. Potato cultivars (Solanum tuberosum) are generally freezing-sensitive, but some potato wild species are freezing-tolerant, including Solanum commersonii, Solanum malmeanum and Solanum acaule. However, the underlying molecular mechanisms conferring the freezing-tolerance to the wild species remain to be deciphered. In this study, five representative genotypes of the above-mentioned species with distinct freezing-tolerance were investigated. Comparative transcriptomics analysis showed that SaCBL1-like (calcineurin B-like protein) was upregulated substantially in all of the freezing-tolerant genotypes. Transgenic overexpression and known-down lines of SaCBL1-like were examined. SaCBL1-like was shown to confer freezing-tolerance without significantly impacting main agricultural traits. A functional mechanism analysis showed that SaCBL1-like increases the expression of the C-repeat binding factor-regulon as well as causes a prolonged higher expression of CBF1 after exposure to cold conditions. Furthermore, SaCBL1-like was found to only interact with SaCIPK3-1 (CBL-interacting protein kinase) among all apparent cold-responsive SaCIPKs. Our study identifies SaCBL1-like to play a vital role in conferring freezing tolerance in potato, which may provide a basis for a targeted potato breeding for frost-hardiness.

Profiling of the Candidate Interacting Proteins of SELF-PRUNING 6A (SP6A) in Solanum tuberosum.

SELF-PRUNING 6A (SP6A), a homolog of FLOWERING LOCUS T (FT), has been identified as tuberigen in potato. StSP6A is a mobile signal synthesized in leaves and transmitted to the stolon through phloem, and plays multiple roles in the growth and development of potato. However, the global StSP6A protein interaction network in potato remains poorly understood. In this study, BK-StSP6A was firstly used as the bait to investigate the StSP6A interaction network by screening the yeast two-hybrid (Y2H) library of potato, resulting in the selection of 200 independent positive clones and identification of 77 interacting proteins. Then, the interaction between StSP6A and its interactors was further confirmed by the Y2H and BiFC assays, and three interactors were selected for further expression analysis. Finally, the expression pattern of Flowering Promoting Factor 1.1 (StFPF1.1), No Flowering in Short Days 1 and 2 (StNFL1 and StNFL2) was studied. The three genes were highly expressed in flowers or flower buds. StFPF1.1 exhibited an expression pattern similar to that of StSP6A at the stolon swelling stages. StPHYF-silenced plants showed up-regulated expression of StFPF1.1 and StSP6A, while expression of StNFL1 and StNFL2 was down-regulated in the stolon. The identification of these interacting proteins lays a solid foundation for further functional studies of StSP6A.

Rychc Confers Extreme Resistance to Potato virus Y in Potato.

The Potato virus Y (PVY) is responsible for huge economic losses for the potato industry worldwide and is the fifth most consequential plant virus globally. The main strategies for virus control are to limit aphid vectors, produce virus-free seed potatoes, and breed virus-resistant varieties. The breeding of PVY-resistant varieties is the safest and most effective method in terms of cost and environmental protection. Rychc, a gene that confers extreme resistance to PVY, is from S. chacoense, which is a wild diploid potato species that is widely used in many PVY-resistant breeding projects. In this study, Rychc was fine mapped and successfully cloned from S. chacoense accession 40-3. We demonstrated that Rychc encodes a TIR-NLR protein by stably transforming a diploid susceptible cultivar named AC142 and a tetraploid potato variety named E3. The Rychc conferred extreme resistance to PVYO, PVYN:O and PVYNTN in both of the genotypes. To investigate the genetic events occurring during the evolution of the Rychc locus, we sequenced 160 Rychc homologs from 13 S. chacoense genotypes. Based on the pattern of sequence identities, 160 Rychc homologs were divided into 11 families. In Family 11 including Rychc, we found evidence for Type I evolutionary patterns with frequent sequence exchanges, obscured orthologous relationships and high non-synonymous to synonymous substitutions (Ka/Ks), which is consistent with rapid diversification and positive selection in response to rapid changes in the PVY genomes. Furthermore, a functional marker named MG64-17 was developed in this study that indicates the phenotype with 100% accuracy and, therefore, can be used for marker-assisted selection in breeding programs that use S. chacoense as a breeding resource.

The transcription factor StTINY3 enhances cold-induced sweetening resistance by coordinating starch resynthesis and sucrose hydrolysis in potato.

The accumulation of reducing sugars in cold-stored tubers, known as cold-induced sweetening (CIS), negatively affects potato processing quality. The starch to sugar interconversion pathways that are altered in cold-stored CIS tubers have been elucidated, but the mechanism that regulates them remains largely unknown. This study identified a CBF/DREB transcription factor (StTINY3) that enhances CIS resistance by both activating starch biosynthesis and repressing the hydrolysis of sucrose to reducing sugars in detached cold-stored tubers. Silencing StTINY3 in a CIS-resistant genotype decreased CIS resistance, while overexpressing StTINY3 in a CIS-sensitive genotype increased CIS resistance, and altering StTINY3 expression was associated with expression changes in starch resynthesis-related genes. We showed first that overexpressing StTINY3 inhibited sucrose hydrolysis by enhancing expression of the invertase inhibitor gene StInvInh2, and second that StTINY3 promoted starch resynthesis by up-regulating a large subunit of the ADP-glucose pyrophosphorylase gene StAGPaseL3, and the glucose-6-phosphate transporter gene StG6PT2. Using electrophoretic mobility shift assays, we revealed that StTINY3 is a nuclear-localized transcriptional activator that directly binds to the dehydration-responsive element/CRT cis-element in the promoters of StInvInh2 and StAGPaseL3. Taken together, these findings established that StTINY3 influences CIS resistance in cold-stored tubers by coordinately modulating the starch to sugar interconversion pathways and is a good target for improving potato processing quality.

Global Screening and Functional Identification of Major HSPs Involved in PVY Infection in Potato.

HSP40 (also known as DnaJ), HSP70, and HSP90 are major heat shock protein (HSP) families that play critical roles in plant growth and development and stress adaption. Recently, several members of the three HSP families were reported to be widely involved in the plant host-virus interactions. However, their global expression profiles and core members recruited by viruses are largely unknown. In this study, a total of 89 StDnaJs were identified from a genome-wide survey, and their classification, phylogenetic relationships, chromosomal locations, and gene duplication events were further analyzed. Together with 20 StHSP70s and 7 StHSP90s previously identified in the potato genome, the global expression patterns of the members in 3 HSP families were investigated in 2 potato cultivars during Potato virus Y (PVY) infection using RNA-seq data. Of them, 16 genes (including 8 StDnaJs, 6 StHSP70s, and 2 StHSP90s) were significantly up- or downregulated. Further analysis using qRT-PCR demonstrated that 7 of the 16 genes (StDnaJ06, StDnaJ17, StDnaJ21, StDnaJ63, StHSP70-6, StHSP70-19, and StHSP90.5) were remarkably upregulated in the potato cultivar 'Eshu 3' after PVY infection, implying their potential roles in the potato-PVY compatible interaction. Subsequent virus-induced gene silencing (VIGS) assays showed that silencing of the homologous genes of StDnaJ17, StDnaJ21, StHSP70-6, and StHSP90.5 in Nicotiana. benthamiana plants dramatically reduced the accumulation of PVY, which indicated the four genes may function as susceptibility factors in PVY infection. This study provides candidate genes for exploring the mechanism of potato-PVY compatible interaction and benefits breeding work aiming to produce new cultivars with the ability to grow healthily under PVY infection.

Transcription factor StABI5-like 1 binding to the FLOWERING LOCUS T homologs promotes early maturity in potato.

Potato (Solanum tuberosum L.) maturity involves several important traits, including the onset of tuberization, flowering, leaf senescence, and the length of the plant life cycle. The timing of flowering and tuberization in potato is mediated by seasonal fluctuations in photoperiod and is thought to be separately controlled by the FLOWERING LOCUS T-like (FT-like) genes SELF-PRUNING 3D (StSP3D) and SELF-PRUNING 6A (StSP6A). However, the biological relationship between these morphological transitions that occur almost synchronously remains unknown. Here, we show that StABI5-like 1 (StABL1), a transcription factor central to abscisic acid (ABA) signaling, is a binding partner of StSP3D and StSP6A, forming an alternative florigen activation complex and alternative tuberigen activation complex in a 14-3-3-dependent manner. Overexpression of StABL1 results in the early initiation of flowering and tuberization as well as a short life cycle. Using genome-wide chromatin immunoprecipitation sequencing and RNA-sequencing, we demonstrate that AGAMOUS-like and GA 2-oxidase 1 genes are regulated by StABL1. Phytohormone profiling indicates an altered gibberellic acid (GA) metabolism and that StABL1-overexpressing plants are insensitive to the inhibitory effect of GA with respect to tuberization. Collectively, our results suggest that StABL1 functions with FT-like genes to promote flowering and tuberization and consequently life cycle length in potato, providing insight into the pleiotropic functioning of the FT gene.

Modulation of JA signalling reveals the influence of StJAZ1-like on tuber initiation and tuber bulking in potato.

Phytohormones and their interactions play critical roles in Solanum tuberosum (potato) tuberization. The stimulatory role of jasmonic acid (JA) in tuber development is well established because of its significant promotion of tuber initiation and tuber bulking. However, the dynamics and potential function of JA signalling in potato tuberization remain largely unknown. The present study investigated the role of the JAZ1 subtype, a suppressor of JA signalling, in potato tuberization. Using 35S:StJAZ1-like-GUS as a reporter, we showed that JA signalling was attenuated from the bud end to the stem end shortly after tuber initiation. Overexpression of StJAZ1-like suppressed tuber initiation by restricting the competence for tuber formation in stolon tips, as demonstrated by grafting an untransformed potato cultivar to the stock of StJAZ1-like-overexpressing transgenic potato plants (StJAZ1-like ox). In addition, transcriptional profiling analysis revealed that StJAZ1-like modulates the expression of genes associated with transcriptional regulators, cell cycle, cytoskeleton and phytohormones. Furthermore, we showed that StJAZ1-like is destabilised upon treatment with abcisic acid (ABA), and the attenuated tuberization phenotype in StJAZ1-like ox plants can be partially rescued by ABA treatment. Altogether, these results revealed that StJAZ1-like-mediated JA signalling plays an essential role in potato tuberization.

Suppression of the tonoplast sugar transporter StTST3.2 improves quality of potato chips.

Which sugar transporter regulates sugar accumulation in tubers is largely unknown. Accumulation of reducing sugar (RS) in potato (Solanum tuberosum L.) tubers negatively affects the quality of tubers undergoing the frying process. However, little is known about the genes involved in regulating RS content in tubers at harvest. Here, we have identified two tonoplast sugar transporter (TST) 3-type isoforms (StTST3.1 and StTST3.2) in potato. Quantitative real-time PCR results indicate that StTST3.1 and StTST3.2 possess distinct expression patterns in various potato tissues. StTST3.2 was found to be the expressed TST3-type isoform in tubers. Further subcellular localization analysis revealed that StTST3.2 was targeted to the tonoplast. Silencing of StTST3.2 in potato by stable transformation resulted in significantly lower RS content in tubers at harvest or after room temperature storage, suggesting StTST3.2 plays an important role in RS accumulation in tubers. Accordingly, compared with the unsilenced control, potato chips processed from StTST3.2-silenced tubers exhibited lighter color and dramatically decreased acrylamide production at harvest or after room temperature storage. In addition, we demonstrated that silencing of StTST3.2 has no significant effect on potato growth and development. Thus, suppression of StTST3.2 could be another effective approach for improving processing quality and decreasing acrylamide content in potato tubers.