Amylases StAmy23, StBAM1 and StBAM9 regulate cold-induced sweetening of potato tubers in distinct ways

Understanding starch biosynthesis in potatoes for metabolic engineering to improve starch quality: A detailed review

Potato tubers accumulate substantial quantities of starch, which serves as their primary energy reserve. As the predominant component of potato tubers, starch strongly influences tuber yield, processing quality, and nutritional attributes. Potato starch is distinguished from other food starches by its unique granule morphology and compositional attributes. It possesses large, oval granules with amylose content ranging from 20 to 33 % and high phosphorus levels, which collectively determine the unique physicochemical characteristics. These physicochemical properties direct the utility of potato starch across diverse food and industrial applications. This review synthesizes current knowledge on the molecular factors controlling potato starch biosynthesis and structure-function relationships. Key topics covered are starch granule morphology, the roles and regulation of major biosynthetic enzymes, transcriptional and hormonal control, genetic engineering strategies, and opportunities to tailor starch functionality. Elucidating the contributions of different enzymes in starch biosynthesis has enabled targeted modification of potato starch composition and properties. However, realizing the full potential of this knowledge faces challenges in optimizing starch quality without compromising plant vigor and yield. Overall, integrating multi-omics datasets with advanced genetic and metabolic engineering tools can facilitate the development of elite cultivars with enhanced starch yield and tailored functionalities.

Molecular and biochemical components associated with chilling tolerance in tomato: comparison of different developmental stages

The cultivated tomato, Solanum lycopersicum, is highly sensitive to cold stress (CS), resulting in significant losses during cultivation and postharvest fruit storage. Previously, we demonstrated the presence of substantial genetic variation in fruit chilling tolerance in a tomato recombinant inbred line (RIL) population derived from a cross between a chilling-sensitive tomato line and a chilling-tolerant accession of the wild species S. pimpinellifolium. Here, we investigated molecular and biochemical components associated with chilling tolerance in fruit and leaves, using contrasting groups of "chilling tolerant" and "chilling sensitive" RI lines. Transcriptomic analyses were conducted on fruit exposed to CS, and gene expressions and biochemical components were measured in fruit and leaves. The analyses revealed core responding genes specific to either the cold-tolerant or cold-sensitive RI lines, which were differentially regulated in similar fashion in both leaves and fruit within each group. These genes may be used as markers to determine tomato germplasm cold tolerance or sensitivity. This study demonstrated that tomato response to CS in different developmental stages, including seedling and postharvest fruit, might be mediated by common biological/genetic factors. Therefore, genetic selection for cold tolerance during early stages of plant development may lead to lines with greater postharvest fruit chilling tolerance.

Effects of Exocellobiohydrolase CBHA on Fermentation of Tobacco Leaves

The quality of tobacco is directly affected by macromolecular content, fermentation is an effective method to improve biochemical properties. In this study, we utilized CBHA (cellobiohydrolase A) glycosylase, which was expressed by Pichia pastoris, as an additive for fermentation. The contents of main chemical components of tobacco leaves after fermentation were determined, and the changes of microbial community structure and abundance in tobacco leaves during fermentation were analyzed. The relationship between chemical composition and changes in microbial composition was investigated, and the function of bacteria and fungi in fermentation was predicted to identify possible metabolic pathways. After 48 h of CBHA fermentation, the contents of starch, cellulose and total nitrogen in tobacco leaf decreased by 17.60%, 28.91% and 16.05%, respectively. The microbial community structure changed significantly, with Aspergillus abundance decreasing significantly, while Filobasidum, Cladosporium, Bullera, Komagataella, etc., increased in CBHA treated group. Soluble sugar was most affected by microbial community in tobacco leaves, which was negatively correlated with starch, cellulose and total nitrogen. During the fermentation process, the relative abundance of metabolism-related functional genes increased, and the expressions of cellulase and endopeptidase also increased. The results showed that the changes of bacterial community and dominant microbial community on tobacco leaves affected the content of chemical components in tobacco leaves, and adding CBHA for fermentation had a positive effect on improving the quality of tobacco leaves.

Potato: from functional genomics to genetic improvement

Potato is the most widely grown non-grain crop and ranks as the third most significant global food crop following rice and wheat. Despite its long history of cultivation over vast areas, slow breeding progress and environmental stress have led to a scarcity of high-yielding potato varieties. Enhancing the quality and yield of potato tubers remains the ultimate objective of potato breeding. However, conventional breeding has faced challenges due to tetrasomic inheritance, high genomic heterozygosity, and inbreeding depression. Recent advancements in molecular biology and functional genomic studies of potato have provided valuable insights into the regulatory network of physiological processes and facilitated trait improvement. In this review, we present a summary of identified factors and genes governing potato growth and development, along with progress in potato genomics and the adoption of new breeding technologies for improvement. Additionally, we explore the opportunities and challenges in potato improvement, offering insights into future avenues for potato research.

Molecular Characteristics and Functional Identification of a Key Alpha-Amylase-Encoding Gene AMY11 in Musa acuminata

Alpha-amylase (AMY) plays a significant role in regulating the growth, development, and postharvest quality formation in plants. Nevertheless, little is known about the genome-wide features, expression patterns, subcellular localization, and functional regulation of AMY genes (MaAMYs) in the common starchy banana (Musa acuminata). Twelve MaAMY proteins from the banana genome database were clustered into two groups and contained a conserved catalytic domain. These MaAMYs formed collinear pairs with the AMYs of maize and rice. Three tandem gene pairs were found within the MaAMYs and are indicative of putative gene duplication events. Cis-acting elements of the MaAMY promoters were found to be involved in phytohormone, development, and stress responses. Furthermore, MaAMY02, 08, 09, and 11 were actively expressed during fruit development and ripening. Specifically, MaAMY11 showed the highest expression level at the middle and later stages of banana ripening. Subcellular localization showed that MaAMY02 and 11 were predominately found in the chloroplast, whereas MaAMY08 and 09 were primarily localized in the cytoplasm. Notably, transient attenuation of MaAMY11 expression resulted in an obvious increase in the starch content of banana fruit, while a significant decrease in starch content was confirmed through the transient overexpression of MaAMY11. Together, these results reveal new insights into the structure, evolution, and expression patterns of the MaAMY family, affirming the functional role of MaAMY11 in the starch degradation of banana fruit.

Comparing the differences in quality profiles and antioxidant activity in seven pumpkin cultivars (Cucurbita moschata and Cucurbita maxima) at harvest and during postharvest storage

Pumpkin, nutritious vegetable, is renowned for its extended shelf life. In this study, seven pumpkin cultivars from Cucurbita moschata and Cucurbita maxima were comparatively characterized for 25 physiochemical quality factors, starch granule structures, antioxidant activity, and correlations at 0-60 days of postharvest (dop). The findings revealed that sucrose and carotenoid contents increased in C. moschata, while they initially increased and then decreased in C. maxima. Additionally, acidity, primarily driven by malic acid, decreased in C. maxima but increased in C. maxima. The starch content of C. moschata and C. maxima reached its maximum value at 30 dop and 20 dop, respectively. The DPPH radical scavenging activity correlated with the carotenoid content in both pumpkin species. Conclusively, C. moschata demonstrated improved nutritional and quality at 20-30 dop, while C. maxima exhibited higher commercial suitability at 10-20 dop. The findings suggested that pumpkin storage was crucial for quality improvement.

Genome-Wide Identification and Expression Profiling of the α-Amylase (AMY) Gene Family in Potato

Starch degradation provides energy and signaling molecules for plant growth, development, defense, and stress response. α-amylase (AMY) is one of the most important enzymes in this process. Potato tubers are rich in starch, and the hydrolysis of starch into sugar negatively impacts the frying quality of potato. Despite its importance, the AMY gene family has not been fully explored in potatoes. Here, we performed a detailed analysis of the StAMY gene family to determine its role in potato. Twenty StAMY genes were identified across the potato genome and were divided into three subgroups. The promoters of StAMY genes contained an array of cis-acting elements involved in growth and development, phytohormone signaling, and stress and defense responses. StAMY8, StAMY9, StAMY12, and StAMY20 were specifically expressed in mature tubers. Different StAMY gene family members tended to be upregulated in response to β-aminobutyric acid (BABA), Phytophthora infestans (P. infestans), benzothiadiazole (BTH), heat, salt, and drought stress. In addition, different StAMY gene family members tended to be responsive to abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellic acid (GA3), and 6-benzylaminopurine (BAP) treatment. These results suggest that StAMY gene family members may be involved in starch and sugar metabolism, defense, stress response, and phytohormone signaling. The results of this study may be applicable to other starchy crops and lay a foundation for further research on the functions and regulatory mechanisms of AMY genes.

Identification of potato varieties suitable for cold storage and reconditioning: A safer alternative to anti-sprouting chemicals for potato sprouting control

Low temperature storage as an alternative to anti-sprouting chemicals in potato storage may induce reducing sugars (RS) accumulation (i.e. glucose and fructose) in potato tubers. This phenomenon is called "cold induced sweetening" (CIS) and occurs in certain varieties. CIS leads to a decrease in the organoleptic qualities and darkening of processed potato and the accumulation of toxic molecules such as acrylamide. To identify potato varieties suitable for storage at low temperatures, we screened six commercial processing varieties: Lady Claire (LC), Verdi, Kiebitz (KB), Pirol, Agria and Markies for their CIS characteristics and sprout-forming potential after storage at 4 °C and 8 °C. Our findings reveal that 4 °C storage allows for efficient sprout reduction in all six tested varieties for up to 4.5 months of storage. Three CIS-resistant varieties, namely Verdi, Lady Claire and Kiebitz, were identified as able to be stored for up to four months at 4 °C with limited increase in glucose content. Conversely, Pirol, Agria and Markies showed an increase in glucose content with a decrease in storage temperature and can be considered as CIS-susceptible varieties. After processing into crisps, the CIS-susceptible varieties displayed poor crisp color quality (brown to black color crisps) after storage for two months at 4 °C compared to the storage at 8 °C, whereas the CIS-resistant varieties had good crisp color quality (pale yellow color crisps) after storage at both 4 and 8 °C. Interestingly, the trends of total RS and/or glucose content in the CIS-resistant and in the CIS-susceptible varieties were correlated with the trends in Vacuolar Invertase (VInv) gene expression for most varieties, as well as with the trends in acrylamide content after processing. In addition, reconditioning of Markies variety after storage at 4 °C by gradually increasing the temperature to 15 °C resulted in a significant decrease of VInv transcript levels (reduction of 80 %), acrylamide content (reduction of 75 %) and glucose content when compared to a storage at 4 °C without reconditioning. Those results demonstrate that the reconditioning technique is a key factor for a sustainable potato storage and for improving the quality of processed potatoes.

Comprehensive Identification of the β-Amylase (BAM) Gene Family in Response to Cold Stress in White Clover

White clover (Trifolium repens L.) is an allopolyploid plant and an excellent perennial legume forage. However, white clover is subjected to various stresses during its growth, with cold stress being one of the major limiting factors affecting its growth and development. Beta-amylase (BAM) is an important starch-hydrolyzing enzyme that plays a significant role in starch degradation and responses to environmental stress. In this study, 21 members of the BAM gene family were identified in the white clover genome. A phylogenetic analysis using BAMs from Arabidopsis divided TrBAMs into four groups based on sequence similarity. Through analysis of conserved motifs, gene duplication, synteny analysis, and cis-acting elements, a deeper understanding of the structure and evolution of TrBAMs in white clover was gained. Additionally, a gene regulatory network (GRN) containing TrBAMs was constructed; gene ontology (GO) annotation analysis revealed close interactions between TrBAMs and AMY (α-amylase) and DPE (4-alpha-glucanotransferase). To determine the function of TrBAMs under various tissues and stresses, RNA-seq datasets were analyzed, showing that most TrBAMs were significantly upregulated in response to biotic and abiotic stresses and the highest expression in leaves. These results were validated through qRT-PCR experiments, indicating their involvement in multiple gene regulatory pathways responding to cold stress. This study provides new insights into the structure, evolution, and function of the white clover BAM gene family, laying the foundation for further exploration of the functional mechanisms through which TrBAMs respond to cold stress.

Genome-Wide Identification and Preliminary Functional Analysis of BAM (β-Amylase) Gene Family in Upland Cotton

The β-amylase (BAM) gene family encodes important enzymes that catalyze the conversion of starch to maltose in various biological processes of plants and play essential roles in regulating the growth and development of multiple plants. So far, BAMs have been extensively studied in Arabidopsis thaliana (A. thaliana). However, the characteristics of the BAM gene family in the crucial economic crop, cotton, have not been reported. In this study, 27 GhBAM genes in the genome of Gossypium hirsutum L (G. hirsutum) were identified by genome-wide identification, and they were divided into three groups according to sequence similarity and phylogenetic relationship. The gene structure, chromosome distribution, and collinearity of all GhBAM genes identified in the genome of G. hirsutum were analyzed. Further sequence alignment of the core domain of glucosyl hydrolase showed that all GhBAM family genes had the glycosyl hydrolase family 14 domain. We identified the BAM gene GhBAM7 and preliminarily investigated its function by transcriptional sequencing analysis, qRT-PCR, and subcellular localization. These results suggested that the GhBAM7 gene may influence fiber strength during fiber development. This systematic analysis provides new insight into the transcriptional characteristics of BAM genes in G. hirsutum. It may lay the foundation for further study of the function of these genes.

Genome-Wide Investigation of BAM Gene Family in Annona atemoya: Evolution and Expression Network Profiles during Fruit Ripening

β-amylase proteins (BAM) are important to many aspects of physiological process such as starch degradation. However, little information was available about the BAM genes in Annona atemoya, an important tropical fruit. Seven BAM genes containing the conservative domain of glycoside hydrolase family 14 (PF01373) were identified with Annona atemoya genome, and these BAM genes can be divided into four groups. Subcellular localization analysis revealed that AaBAM3 and AaBAM9 were located in the chloroplast, and AaBAM1.2 was located in the cell membrane and the chloroplast. The AaBAMs belonging to Subfamily I contribute to starch degradation have the higher expression than those belonging to Subfamily II. The analysis of the expression showed that AaBAM3 may function in the whole fruit ripening process, and AaBAM1.2 may be important to starch degradation in other organs. Temperature and ethylene affect the expression of major AaBAM genes in Subfamily I during fruit ripening. These expressions and subcellular localization results indicating β-amylase play an important role in starch degradation.

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 of β-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 starch metabolism regulation during postharvest cold storage. Thus, our findings provide a new strategy to improve the frying quality of cold-stored tubers and reduce the acrylamide content in potato chips.

Mechanical wounds expedited starch degradation in the wound tissues of potato tubers

Starch degradation occurs rapidly in stressed plants, but it is unclear how starch degradation occurs in potato tubers after they incur mechanical wounding. In this study, we found that wounding significantly upregulated the expression levels of StGWD, StAMY, StBAM, and StISA, and decreased the starch content of potato tubers. Meanwhile, wounding markedly upregulated the expression levels of StSUS, StBG, and StINV genes, and increased the content of sucrose, glucose, and fructose. Furthermore, wounding reduced the proportion of small starch granules and increase that of large as well as medium starch granules, in this way enhancing the average size distribution of starch. Initially, the hard surface layer of starch granules was removed by wounding, but the internal channels and other structures were only slightly affected. Taken together, the results show that wounding can accelerate starch degradation by promoting the accumulation of sucrose, glucose, and fructose, and the hydrolysis of starch granules in potato tubers.

Comparative analysis of the transcriptome during single-seed formation of Castanea henryi: regulation of starch metabolism and endogenous hormones

BACKGROUND

In seed plants, the ovule is the precursor to the seed. The process of ovule development and differentiation is regulated by multiple factors, including starch metabolism and endogenous hormones. Castanea henryi produces nuts with high nutritional value. However, the high proportion of empty buds restricts the commercial use of the tree. Previous studies have shown that the empty bud phenotype is closely related to ovule abortion. If none of the ovules in the ovary expand rapidly and develop in 7-8 weeks after pollination, an empty bud will form. Therefore, we studied the development and molecular mechanisms underlying single seed formation in C. henryi.

RESULTS

We found that 49 days after pollination (DAP) is a critical period for the formation of fertile and abortive ovules. The morphology and starch distribution of the fertile and abortive ovules differed significantly at 49 DAP. The fertile ovules were smooth and round in appearance, with a large amount of starch. In contrast, abortive ovules were smaller with only a small amount of starch. The embryo sac of the abortive ovule proceeded to develop abnormally, and the entire ovule lacked starch. We identified 37 candidate genes involved in metabolism with potential roles in the regulation of starch levels. Three ADP-glucose pyrophosphorylase (AGPase) genes, one granule-bound starch synthase (GBSS) gene, and two beta-amylase genes could affect starch accumulation. The levels of auxin, cytokinins, gibberellins, and jasmonic acid in fertile ovules were higher than those in abortive ovules. In addition, the levels of endogenous abscisic acid and salicylic acid in abortive ovules were higher than those in fertile ovules of the same age, consistent with the expression patterns of genes related to the synthesis of abscisic and salicylic acid and signal transduction. We identified and mapped the differentially expressed genes associated with hormone synthesis and signal transduction.

CONCLUSIONS

These results improve our general understanding of the molecular mechanisms underlying single seed development in C. henryi and the phenomenon of empty buds, providing directions for future research.

Low temperature reduces potato wound formation by inhibiting phenylpropanoid metabolism and fatty acid biosynthesis

INTRODUCTION

Potato tubers have the healing capacity to prevent surface water transpiration and pathogen invasion after mechanical damage. Previous research has shown the inability to form healing periderm in potatoes under low temperatures, but the potential mechanism is still unclear.

METHODS

To explore the effects and mechanisms of low-temperature potato healing, wounded potatoes were stored at low temperature (4°C) and room temperature (22°C), respectively.

RESULTS

In this study, compared with 22°C healing, low temperature reduced the content of hydrogen peroxide, and the down-regulation of StAMY23 inhibited the conversion of starch to sugar, alleviated the degradation of starch, and reduced the content of soluble sugars and sucrose. Meanwhile, inhibition of phenylalanine metabolism by suppression of StPAL1 and St4CL expression reduced lignin accumulation. Low temperature also down-regulated the expression of StKCS6, StFAOH, StGPAT5, and StPrx, causing the lower deposition amount of suberin in wounds of potato tubers.

DISCUSSION

The above results suggested that low temperature led to less wound tissue deposition at the wound surfaces via suppressing phenylpropanoid metabolism and fatty acid biosynthesis in potato tubers.

VaBAM1 weakens cold tolerance by interacting with the negative regulator VaSR1 to suppress β-amylase expression

Cold stress is a key climatic factor that limits grape productivity and quality. Although β-amylase (BAM) is known to play an important role as a mediator of starch degradation under conditions of cold stress, the mechanism by which BAM regulates cold tolerance in grape remains unclear. Here, we identified VaBAM1 from Vitis amurensis and characterized its interactive regulating mechanism under cold stress in Arabidopsis thaliana and grape. VaBAM1-overexpressing A. thaliana plants (OEs) exhibited high freezing tolerance. Soluble sugar content and amylase activity were increased in OEs and VaBAM1-overexpressing grape calli (VaBAM1-OEs) under cold stress; however, they were decreased in grape calli in which VaBAM1 was edited using CRISPR/Cas9. The results of yeast two-hybrid, bimolecular fluorescence complementation, and pull-down experiments showed that serine/arginine-rich splicing factor 1 (VaSR1) interacted with VaBAM1. Furthermore, the expression of VaSR1 was opposite that of VaBAM1 in phloem tissue of Vitis amurensis during winter dormancy. In VaSR1-overexpressing grape calli (VaSR1-OEs), BAM activity and the expression levels of C-repeat binding transcription factor and cold response genes were all significantly lower than that in untransformed calli subjected to cold stress. Moreover, VvBAM1 was downregulated in VaSR1-OEs under cold stress. Overall, we identified that VaSR1 interacts with VaBAM1, negatively regulating BAM activity and resulting in decreased plant cold tolerance.

An alternative pathway to plant cold tolerance in the absence of vacuolar invertase activity

To cope with cold stress, plants have developed antioxidation strategies combined with osmoprotection by sugars. In potato (Solanum tuberosum) tubers, which are swollen stems, exposure to cold stress induces starch degradation and sucrose synthesis. Vacuolar acid invertase (VInv) activity is a significant part of the cold-induced sweetening (CIS) response, by rapidly cleaving sucrose into hexoses and increasing osmoprotection. To discover alternative plant tissue pathways for coping with cold stress, we produced VInv-knockout lines in two cultivars. Genome editing of VInv in 'Désirée' and 'Brooke' was done using stable and transient expression of CRISPR/Cas9 components, respectively. After storage at 4°C, sugar analysis indicated that the knockout lines showed low levels of CIS and maintained low acid invertase activity in storage. Surprisingly, the tuber parenchyma of vinv lines exhibited significantly reduced lipid peroxidation and reduced H2 O2 levels. Furthermore, whole plants of vinv lines exposed to cold stress without irrigation showed normal vigor, in contrast to WT plants, which wilted. Transcriptome analysis of vinv lines revealed upregulation of an osmoprotectant pathway and ethylene-related genes during cold temperature exposure. Accordingly, higher expression of antioxidant-related genes was detected after exposure to short and long cold storage. Sugar measurements showed an elevation of an alternative pathway in the absence of VInv activity, raising the raffinose pathway with increasing levels of myo-inositol content as a cold tolerance response.

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.

Elucidating the role of MaBAM9b in starch degradation

Banana is a typical starch conversion fruit. The high content of starch at harvest is quickly digested and converted to soluble sugars during the postharvest ripening process, ultimately contributing to fruit flavor. This process is regulated in a complex manner by genes and environmental factors. MaBAM9b is one of the main enzyme genes previously found by transcriptomic analysis to be highly expressed in banana fruit. However, its exact role in starch degradation remains unclear. Here, full-length MaBAM9b was isolated from banana fruit, and its subcellular localization, protein expression, and transient expression in banana fruit slices were investigated. In addition, sense and anti-sense MaBAM9b were transformed into rice (Oryza sativa L. japonica. cv. 'Nipponbare') to identify the function of MaBAM9b. MaBAM9b was 1599 bp and encoded 532 amino acids. It contained two conserved domains of PLN02803 and glycosyl hydrolase family 14 and was localized in the chloroplast. The protein expression pattern of MaBAM9b remained consistently high throughout banana fruit ripening and starch degradation. Transient overexpression or inhibition of MaBAM9b in banana fruit greatly improved or suppressed starch degradation. Genetic modification of rice indicated that overexpression of MaBAM9b greatly improved starch degradation and seed germination, while inhibition of its expression suppressed these biological processes. These results support the key role of MaBAM9b in starch degradation and provide a target gene for banana fruit quality improvement and biological breeding.

Comparative Proteomics of Potato Cultivars with a Variable Dormancy Period

The control of the duration of the dormancy phase is a significant challenge in the potato industry and for seed producers. However, the proteome landscape involved in the regulation of the length of the dormancy period over potato cultivars remains largely unexplored. In this study, we performed for the first time a comparative proteome profiling of potato cultivars with differential duration of tuber dormancy. More specifically, the proteome profiling of Agata, Kennebec and Agria commercial potato varieties with short, medium and medium-long dormancy, respectively, was assessed at the endodormancy stage using high-resolution two-dimensional electrophoresis (2-DE) coupled to reversed-phase liquid chromatography–tandem mass spectrometry (LC-TripleTOF MS/MS). A total of 11 proteins/isoforms with statistically significant differential abundance among cultivars were detected on 2-DE gels and confidently identified by LC-TripleTOF MS/MS. Identified proteins have known functions related to tuber development, sprouting and the oxylipins biosynthesis pathway. Fructokinase, a mitochondrial ADP/ATP carrier, catalase isozyme 2 and heat shock 70 kDa were the proteins with the strongest response to dormancy variations. To the best of our knowledge, this study reports the first candidate proteins underlying variable dormancy length in potato cultivars.

Dependence of the content of starch and reducing sugars on the level of expression of the genes of β-amylases StBAM1 and StBAM9 and the amylase inhibitor StAI during long-term low-temperature storage of potato tubers

Solanum tuberosum L. is the most important non-grain starch crop with a potential yield of 38-48 t/ha and a starch content of 13.2-18.7 %. Potato tubers are stored at a low temperature (2-4 °C) in a state of physiological dormancy. A disadvantage of this type of storage is the degradation of starch and the accumulation of reducing sugars (cold-induced sweetening), including due to an increase in the activity of β-amylases that hydrolyze starch to maltose. In this study, a comparative analysis of the β-amylase (StBAM1, StBAM9) and amylase inhibitor (StAI ) gene expression, as well as starch and reducing sugar content in tubers during long-term low-temperature storage (September, February, April) was performed using potato cultivars Nadezhda, Barin, Krasavchik, Severnoe siyanie and Utro. The β-amylase genes, StBAM9 and one of the two StBAM1 homologs (with the highest degree of homology with AtBAM1), were selected based on phylogenetic analysis data. Evaluation of the expression of these genes and the amylase inhibitor gene showed a tendency to decrease in transcription for all analyzed cultivars. The starch content also significantly decreased during tuber storage. The amount of reducing sugars increased in the September-April period, while in February-April, their content did not change (Krasavchik), decreased (Barin, Severnoe siyanie) or continued to grow (Utro, Nadezhda). It can be assumed that the gene activity of StBAM1 and StBAM9 correlates with the amount of starch (positively) and monosaccharides (negatively). The level of StAI expression, in turn, may be directly dependent on the level of StBAM1 expression. At the same time, there is no relationship between the degree of cultivar predisposition to cold-induced sweetening and the expression profile of the StBAM1, StBAM9, and StAI genes.

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.

Genome-wide identification of BAM (β-amylase) gene family in jujube (Ziziphus jujuba Mill.) and expression in response to abiotic stress

BACKGROUND

Elevated temperature and drought stress have substantial impacts on fruit quality, especially in terms of sugar metabolism and content. β-Amylase (BAM) plays a critical role in regulating jujube fruit sugar levels and abiotic stress response. Nevertheless, little is known about the regulatory functions of the BAM genes in jujube fruit.

RESULTS

Nine jujube BAM genes were identified, clustered into four groups, and characterized to elucidate their structure, function, and distribution. Multiple sequence alignment and gene structure analysis showed that all ZjBAM genes contain Glu-186 and Glu-380 residues and are highly conserved. Phylogenetic and synteny analysis further indicated that the ZjBAM gene family is evolutionarily conserved and formed collinear pairs with the BAM genes of peach, apple, poplar, Arabidopsis thaliana, and cucumber. A single tandem gene pair was found within the ZjBAM gene family and is indicative of putative gene duplication events. We also explored the physicochemical properties, conserved motifs, and chromosomal and subcellular localization of ZjBAM genes as well as the interaction networks and 3D structures of ZjBAM proteins. A promoter cis-acting element analysis suggested that ZjBAM promoters comprise elements related to growth, development, phytohormones, and stress response. Furthermore, a metabolic pathways annotation analysis showed that ZjBAMs are significantly upregulated in the starch and sucrose metabolism, thereby controlling starch-maltose interconversion and hydrolyzing starch to maltose. Transcriptome and qRT-PCR analyses revealed that ZjBAMs respond positively to elevated temperature and drought stress. Specifically, ZjBAM1, ZjBAM2, ZjBAM5, and ZjBAM6 are significantly upregulated in response to severe drought. Bimolecular fluorescence complementation analysis demonstrated ZjBAM1-ZjAMY3, ZjBAM8-ZjDPE1, and ZjBAM7-ZjDPE1 protein interactions that were mainly present in the plasma membrane and nucleus.

CONCLUSION

The jujube BAM gene family exhibits high evolutionary conservation. The various expression patterns of ZjBAM gene family members indicate that they play key roles in jujube growth, development, and abiotic stress response. Additionally, ZjBAMs interact with α-amylase and glucanotransferase. Collectively, the present study provides novel insights into the structure, evolution, and functions of the jujube BAM gene family, thus laying a foundation for further exploration of ZjBAM functional mechanisms in response to elevated temperature and drought stress, while opening up avenues for the development of economic forests in arid areas.

Starch metabolism in potato <i>Solanum tuberosum</i> L

Starch is a major storage carbohydrate in plants. It is an important source of calories in the human and animal diet. Also, it is widely used in various industries. Native starch consists of water-insoluble semicrystalline granules formed by natural glucose polymers amylose and amylopectin. The physicochemical properties of starch are determined by the amylose:amylopectin ratio in the granule and degrees of their polymerization and phosphorylation. Potato Solanum tuberosum L. is one of the main starch-producing crops. Growing industrial needs necessitate the breeding of plant varieties with increased starch content and specified starch properties. This task demands detailed information on starch metabolism in the producing plant. It is a complex process, requiring the orchestrated work of many enzymes, transporter and targeting proteins, transcription factors, and other regulators. Two types of starch are recognized with regard to their biological functions. Transitory starch is synthesized in chloroplasts of photosynthetic organs and degraded in the absence of light, providing carbohydrates for cell needs. Storage starch is synthesized and stored in amyloplasts of storage organs: grains and tubers. The main enzymatic reactions of starch biosynthesis and degradation, as well as carbohydrate transport and metabolism, are well known in the case of transitory starch of the model plant Arabidopsis thaliana. Less is known about features of starch metabolism in storage organs, in particular, potato tubers. Several issues remain obscure: the roles of enzyme isoforms and different regulatory factors in tissues at various plant developmental stages and under different environmental conditions; alternative enzymatic processes; targeting and transport proteins. In this review, the key enzymatic reactions of plant carbohydrate metabolism, transitory and storage starch biosynthesis, and starch degradation are discussed, and features specific for potato are outlined. Attention is also paid to the known regulatory factors affecting starch metabolism

Starch Degradation and Sucrose Accumulation of Lily Bulbs after Cold Storage

Functional lilies are a group of edible lily cultivars with great potential for landscape application. Low-temperature storage can significantly improve their taste, but the knowledge of this process is largely unknown. In this study, we used the functional lilies 'Fly Shaohua' and 'Fly Tiancheng' as materials. Through physiological observation and transcriptome analysis during the bulbs' cold storage, it was found that the starch degradation and sucrose accumulation in bulbs contributed to taste improvement. After 60 d of cold storage, the sucrose accumulation was highest and the starch content was lower in the bulbs, suggesting this time-point was optimal for consumption. Accompanying the fluctuation of sucrose content during cold storage, the enzyme activities of sucrose phosphate synthase and sucrose synthase for sucrose synthesis were increased. Transcriptome analysis showed that many differentially expressed genes (DEGs) were involved in the starch and sucrose metabolism pathway, which might promote the conversion of starch to sucrose in bulbs. In addition, the DEGs involved in dormancy and stress response were also determined during cold storage, which might explain the decreased sucrose accumulation with extended storage time over 60 d due to the energy consumption for dormancy release. Taken together, our results indicated sucrose accumulation was a main factor in the taste improvement of lily bulbs after cold storage, which is attributable to the different gene expression of starch and sucrose metabolism pathways in this process.

Biochemical characterization and overexpression of an α-amylase (BmAmy) in silkworm, Bombyx mori

Silkworm (Bombyx mori) is the only fully domesticated insect. As an economically important insect, nutrition utilization is important for its productivity. Hence, the present study investigated the expression pattern of BmAmy, an α-amylase, in B. mori. BmAmy protein purification and biochemical characterization were performed, and effects of BmAmy overexpression were assessed. Real-time quantitative reverse transcription polymerase chain reaction indicated that BmAmy transcription was positively correlated with the silkworm's food intate. Moreover, enzymatic activity assay results showed that BmAmy had significant α-amylase activity of about 1 mg/min/mg protein. Furthermore, treatment with mulberry amylase inhibitors MnAI1 and MnAI2 resulted to 89.92% and 93.67% inhibition in BmAmy activity, respectively, and the interaction between BmAmy and MnAI was also confirmed by protein docking analysis. A silkworm line that specifically overexpressed BmAmy in the midgut was generated through piggyBac-based transgenic technology, and compared to those of non-transgenic silkworms, the whole cocoon and cocoon shell weights of these transgenic silkworms increased by 10.13% and 18.32%, respectively, in the female group, and by 5.83% and 6.00%, respectively, in the male group. These results suggested that BmAmy may be a suitable target for breeding better silkworm varieties in the future.

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.

Transcription factor MaMADS36 plays a central role in regulating banana fruit ripening

Bananas are model fruits for studying starch conversion and climactericity. Starch degradation and ripening are two important biological processes that occur concomitantly in banana fruit. Ethylene biosynthesis and postharvest fruit ripening processes, i.e. starch degradation, fruit softening, and sugar accumulation, are highly correlated and thus could be controlled by a common regulatory switch. However, this switch has not been identified. In this study, we transformed red banana (Musa acuminata L.) with sense and anti-sense constructs of the MaMADS36 transcription factor gene (also MuMADS1, Ma05_g18560.1). Analysis of these lines showed that MaMADS36 interacts with 74 other proteins to form a co-expression network and could act as an important switch to regulate ethylene biosynthesis, starch degradation, softening, and sugar accumulation. Among these target genes, musa acuminata beta-amylase 9b (MaBAM9b, Ma05_t07800.1), which encodes a starch degradation enzyme, was selected to further investigate the regulatory mechanism of MaMADS36. Our findings revealed that MaMADS36 directly binds to the CA/T(r)G box of the MaBAM9b promoter to increase MaBAM9b transcription and, in turn, enzyme activity and starch degradation during ripening. These results will further our understanding of the fine regulatory mechanisms of MADS-box transcription factors in regulating fruit ripening, which can be applied to breeding programs to improve fruit shelf-life.

A Traceable DNA-Replicon Derived Vector to Speed Up Gene Editing in Potato: Interrupting Genes Related to Undesirable Postharvest Tuber Traits as an Example

In potato (Solanum tuberosum L.), protoplast techniques are limited to a few genotypes; thus, the use of regular regeneration procedures of multicellular explants causes us to face complexities associated to CRISPR/Cas9 gene editing efficiency and final identification of individuals. Geminivirus-based replicons contained in T-DNAs could provide an improvement to these procedures considering their cargo capability. We built a Bean yellow dwarf virus-derived replicon vector, pGEF-U, that expresses all the editing reagents under a multi-guide RNA condition, and the Green Fluorescent Protein (GFP) marker gene. Agrobacterium-mediated gene transfer experiments were carried out on 'Yagana-INIA', a relevant local variety with no previous regeneration protocol. Assays showed that pGEF-U had GFP transient expression for up to 10 days post-infiltration when leaf explants were used. A dedicated potato genome analysis tool allowed for the design of guide RNA pairs to induce double cuts of genes associated to enzymatic browning (StPPO1 and 2) and to cold-induced sweetening (StvacINV1 and StBAM1). Monitoring GFP at 7 days post-infiltration, explants led to vector validation as well as to selection for regeneration (34.3% of starting explants). Plant sets were evaluated for the targeted deletion, showing individuals edited for StPPO1 and StBAM1 genes (1 and 4 lines, respectively), although with a transgenic condition. While no targeted deletion was seen in StvacINV1 and StPPO2 plant sets, stable GFP-expressing calli were chosen for analysis; we observed different repair alternatives, ranging from the expected loss of large gene fragments to those showing punctual insertions/deletions at both cut sites or incomplete repairs along the target region. Results validate pGEF-U for gene editing coupled to regular regeneration protocols, and both targeted deletion and single site editings encourage further characterization of the set of plants already generated.

The AaCBF4-AaBAM3.1 module enhances freezing tolerance of kiwifruit (Actinidia arguta)

Beta-amylase (BAM) plays an important role in plant resistance to cold stress. However, the specific role of the BAM gene in freezing tolerance is poorly understood. In this study, we demonstrated that a cold-responsive gene module was involved in the freezing tolerance of kiwifruit. In this module, the expression of AaBAM3.1, which encodes a functional protein, was induced by cold stress. AaBAM3.1-overexpressing kiwifruit lines showed increased freezing tolerance, and the heterologous overexpression of AaBAM3.1 in Arabidopsis thaliana resulted in a similar phenotype. The results of promoter GUS activity and cis-element analyses predicted AaCBF4 to be an upstream transcription factor that could regulate AaBAM3.1 expression. Further investigation of protein-DNA interactions by using yeast one-hybrid, GUS coexpression, and dual luciferase reporter assays confirmed that AaCBF4 directly regulated AaBAM3.1 expression. In addition, the expression of both AaBAM3.1 and AaCBF4 in kiwifruit responded positively to cold stress. Hence, we conclude that the AaCBF-AaBAM module is involved in the positive regulation of the freezing tolerance of kiwifruit.

Hormonal and transcriptional analyses provides new insights into the molecular mechanisms underlying root thickening and isoflavonoid biosynthesis in Callerya speciosa (Champ. ex Benth.) Schot

Callerya speciosa (Champ. ex Benth.) Schot is a traditional Chinese medicine characterized by tuberous roots as the main organ of isoflavonoid accumulation. Root thickening and isoflavonoid accumulation are two major factors for yield and quality of C. speciosa. However, the underlying mechanisms of root thickening and isoflavonoid biosynthesis have not yet been elucidated. Here, integrated morphological, hormonal and transcriptomic analyses of C. speciosa tuberous roots at four different ages (6, 12, 18, 30 months after germination) were performed. The growth cycle of C. speciosa could be divided into three stages: initiation, rapid-thickening and stable-thickening stage, which cued by the activity of vascular cambia. Endogenous changes in phytohormones were associated with developmental changes during root thickening. Jasmonic acid might be linked to the initial development of tuberous roots. Abscisic acid seemed to be essential for tuber maturation, whereas IAA, cis-zeatin and gibberellin 3 were considered essential for rapid thickening of tuberous roots. A total of 4337 differentially expressed genes (DEGs) were identified during root thickening, including 15 DEGs participated in isoflavonoid biosynthesis, and 153 DEGs involved in starch/sucrose metabolism, hormonal signaling, transcriptional regulation and cell wall metabolism. A hypothetical model of genetic regulation associated with root thickening and isoflavonoid biosynthesis in C. speciosa is proposed, which will help in understanding the underlying mechanisms of tuberous root formation and isoflavonoid biosynthesis.

Comparative transcriptome reveals distinct starch-sugar interconversion patterns in potato genotypes contrasting for cold-induced sweetening capacity

Potato accumulates large amounts of soluble sugar during cold storage periods. However, a system based understanding of this process is still largely unknown. Here, we compared the dynamic cold-responded transcriptome of genotypes between cold-induced sweetening resistant (CIS-R) and cold-induced sweetening sensitive (CIS-S) in tubers. Comparative transcriptome revealed that activating the pathways of starch degradation, sucrose synthesis and hydrolysis could be common strategies in response to cold in both genotypes. Moreover, the variation in sugar accumulation between genotypes may be due to genetic differences in cold response, which could be mainly explained: CIS-R genotype was active in starch synthesis and attenuated in sucrose hydrolysis by promoting the coordinate expression of aseries ofgenes involved in starch-sugar interconversion. Additionally, transcription factors, the candidate master regulators of starch-sugar interconversion, were discussed. Taken together, this work has provided an avenue for studying the mechanism involved in the regulation of the CIS resistance.

Cold storage reveals distinct metabolic perturbations in processing and non-processing cultivars of potato (Solanum tuberosum L.)

Cold-induced sweetening (CIS) causes considerable losses to the potato processing industry wherein the selection of potato genotypes using biochemical information has found to be advantageous. Here, ¹H NMR spectroscopy was performed to identify metabolic perturbations from tubers of five potato cultivars (Atlantic, Frito Lay-1533, Kufri Jyoti, Kufri Pukhraj, and PU1) differing in their CIS ability and processing characteristics at harvest and after cold storage (4 °C). Thirty-nine water-soluble metabolites were detected wherein significantly affected metabolites after cold storage were categorized into sugars, sugar alcohols, amino acids, and organic acids. Multivariate statistical analysis indicated significant differences in the metabolic profiles among the potato cultivars. Pathway enrichment analysis revealed that carbohydrates, amino acids, and organic acids are the key players in CIS. Interestingly, one of the processing cultivars, FL-1533, exhibited a unique combination of metabolites represented by low levels of glucose, fructose, and asparagine accompanied by high citrate levels. Conversely, non-processing cultivars (Kufri Pukhraj and Kufri Jyoti) showed elevated glucose, fructose, and malate levels. Our results indicate that metabolites such as glucose, fructose, sucrose, asparagine, glutamine, citrate, malate, proline, 4-aminobutyrate can be potentially utilized for the prediction, selection, and development of potato cultivars for long-term storage, nutritional, as well as processing attributes.

Tuber transcriptome profiling of eight potato cultivars with different cold-induced sweetening responses to cold storage

Tubers are vegetative reproduction organs formed from underground extensions of the plant stem. Potato tubers are harvested and stored for months. Storage under cold temperatures of 2-4 °C is advantageous for supressing sprouting and diseases. However, development of reducing sugars can occur with cold storage through a process called cold-induced sweetening (CIS). CIS is undesirable as it leads to darkened color with fry processing. The purpose of the current study was to find differences in biological responses in eight cultivars with variation in CIS resistance. Transcriptome sequencing was done on tubers before and after cold storage and three approaches were taken for gene expression analysis: 1. Gene expression correlated with end-point glucose after cold storage, 2. Gene expression correlated with increased glucose after cold storage (after-before), and 3. Differential gene expression before and after cold storage. Cultivars with high CIS resistance (low glucose after cold) were found to increase expression of an invertase inhibitor gene and genes involved in DNA replication and repair after cold storage. The cultivars with low CIS resistance (high glucose after cold) showed increased expression of genes involved in abiotic stress response, gene expression, protein turnover and the mitochondria. There was a small number of genes with similar expression patterns for all cultivars including genes involved in cell wall strengthening and phospholipases. It is proposed that the pattern of gene expression is related to chilling-induced DNA damage repair and cold acclimation and that genetic variation in these processes are related to CIS.

Combined transcriptomic and proteomic analysis of cold stress induced sugar accumulation and heat shock proteins expression during postharvest potato tuber storage

Plant species differ greatly in their ability to acclimatise to and survive, cold stress. Normally, potato tubers are stored at low temperatures (below 10 °C) to delay sprouting. In this research, combined transcriptomic and proteomic analysis was conducted on potato tubers stored at 15 °C, 4 °C and 0 °C to investigate the mechanism of cold responses during postharvest storage. Results showed that soluble sugars were accumulated under low temperatures, regulating by granule-bound starch synthase 1, beta-amylase, invertase inhibitor and fructokinase. In addition, fifteen heat shock proteins (Hsps), including three Hsp70s, two Hsp80s, one Hsp90, one Hsp100 and eight small Hsps, were induced by low temperatures, which may act individually or synergistically to prevent physiological or cellular damage from cold stress in postharvest potato tubers. This research provided general information of sugar accumulation and defense response in potato tuber under cold storage.

Silencing of α-amylase StAmy23 in potato tuber leads to delayed sprouting

Potato tuber dormancy is critical for the postharvest quality. The supply of carbohydrates is considered as one of the important factors controlling the rate of potato tuber sprouting. Starch is the major carbohydrate reserve in potato tuber, but very little is known about the specific starch degrading enzymes responsible for controlling tuber dormancy and sprouting. In this study, we demonstrate that an α-amylase gene StAmy23 is involved in starch breakdown and regulation of tuber dormancy. Silencing of StAmy23 delayed tuber sprouting by one to two weeks compared with the control. This phenotype is accompanied by reduced levels of reducing sugars and elevated levels of malto-oligosaccharides in tuber cortex and pith tissue below the bud eye of StAmy23-deficient potato tubers. Changes in soluble sugars is accompanied by a slight variation of phytoglycogen structure and starch granule size. Our results suggest that StAmy23 may stimulate sprouting by hydrolyzing soluble phytoglycogen to ensure supply of sugars during tuber dormancy.

Sequence diversity and in silico structure prediction of the vacuolar invertase inhibitor gene from potato (Solanum tuberosum L.) cultivars differing in sugar content

The aim of this study was to examine the variations in sugar content and identify the polymorphism in vacuolar invertase inhibitor (INH2) gene from Indian non-processing (Kufri Jyoti, Kufri Pukhraj and PU1) and exotic processing (Atlantic and Frito Lay-1533) potato cultivars. Upon cold storage (4 °C) processing cultivars maintained low reducing sugars as compared to non-processing cultivars. Sequencing of the INH2 gene identified four alleles of which three identified as novel alleles. A total twelve SNPs resulted in silent mutations, with five conferring the amino acid substitutions. Phylogenetic analysis suggests a highly conserved nature of the INH2 gene. The 3D predicted structures generated for all the alleles revealed slight variations in the orientation of the helices (α1-3) in N-terminal region. Sequence polymorphism observed in INH2 alleles in processing and non-processing potato cultivars can be correlated with the observed variations in the sugar content suggesting a possible role in cold-induced sweetening.

New insights into the origin and evolution of α-amylase genes in green plants

Gene duplication is a source of genetic materials and evolutionary changes, and has been associated with gene family expansion. Functional divergence of duplicated genes is strongly directed by natural selections such as organism diversification and novel feature acquisition. We show that, plant α-amylase gene family (AMY) is comprised of six subfamilies (AMY1-AMY6) that fell into two ancient phylogenetic lineages (AMY3 and AMY4). Both AMY1 and AMY2 are grass-specific and share a single-copy ancestor, which is derived from grass AMY3 genes that have undergone massive tandem and whole-genome duplications during evolution. Ancestral features of AMY4 and AMY5/AMY6 genes have been retained among four green algal sequences (Chrein_08.g362450, Vocart_0021s0194, Dusali_0430s00012 and Monegl_16464), suggesting a gene duplication event following Chlorophyceae diversification. The observed horizontal gene transfers between plant and bacterial AMYs, and chromosomal locations of AMY3 and AMY4 genes in the most ancestral green body (C. reinhardtii), provide evidences for the monophyletic origin of plant AMYs. Despite subfamily-specific sequence divergence driven by natural selections, the active site and SBS1 are well-conserved across different AMY isoforms. The differentiated electrostatic potentials and hydrogen bands-forming residue polymorphisms, further imply variable digestive abilities for a broad substrates in particular tissues or subcellular localizations.

SbRFP1 regulates cold-induced sweetening of potato tubers by inactivation of StBAM1

Potato cold-induced sweetening (CIS) is a major drawback restricting potato process industry. Starch degradation and sucrose decomposition are considered to be the key pathways in potato CIS. Our previous study showed that the RING finger gene SbRFP1 could slow down starch degradation and the accumulation of reducing sugars (RS) through inhibiting amylase and invertase activity in cold-stored tubers. However, the regulation mechanism of SbRFP1 is not clear. In this paper, we first proved that SbRFP1 could promote starch synthesis and modify the shape of starch granules. By further yeast two hybrid, GST-pull down and inhibition of enzyme activity assays, we confirmed that SbRFP1 could slow down the transformation of starch to RS in tubers mainly through the inhibition of β-amylase StBAM1 activity. SbRFP1 was also proved to possess E3 ubiquitin ligase activity by ubiquitination assay. Thus, SbRFP1 may regulate the accumulation of RS in cold-stored tubers by ubiquitination and degradation of StBAM1. Therefore, our study reveals the regulatory mechanism of SbRFP1 in the process of CIS and provides more powerful evidence for the effect of starch degradation on potato CIS.

Effects of (S)-Carvone and Gibberellin on Sugar Accumulation in Potatoes during Low Temperature Storage

Potato tubers (Solanum tuberosum L.) are usually stored at low temperature, which can suppress sprouting and control the occurrence of diseases. However, low temperatures lead potatoes to easily suffer from cold-induced sweetening (CIS), which has a negative effect on food processing. The aim of this research was to investigate potential treatments on controlling CIS in potatoes during postharvest storage. “Atlantic” potatoes were treated with gibberellin and (S)-carvone, respectively, and stored at 4 °C for 90 days. The results showed that gibberellin can significantly accelerate sprouting and sugar accumulation by regulating expressions of ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), β-amylase (BAM1/2), UDP-glucose pyrophosphorylase (UGPase) and invertase inhibitor (INH1/2) genes. The opposite effects were found in the (S)-carvone treatment group, where CIS was inhibited by modulation of the expressions of GBSS and INH1/2 genes. In summary, gibberellin treatment can promote sugar accumulation while (S)-carvone treatment has some effects on alleviating sugar accumulation. Thus, (S)-carvone can be considered as a potential inhibitor of some of the sugars which are vital in controlling CIS in potatoes. However, the chemical concentration, treatment time, and also the treatment method needs to be optimized before industrial application.

Review: The Arabidopsis β-amylase (BAM) gene family: Diversity of form and function

Multi-gene families present a rich research area to study how related proteins evolve to acquire new structures and functions. The β-amylase (BAM) gene family is named for catalytic members' ability to hydrolyze starch into maltose units. However, the family also contains proteins that are catalytically inactive, have additional domains, or are not localized with a starch substrate. Here we review the current knowledge of each of the nine Arabidopsis BAMs, including information on their localization, structural features, expression patterns, regulation and potential functions. We also discuss unique characteristics of studying multi-gene families, such as the consideration of different kinetic parameters when performing assays on leaf extracts, and suggest approaches that may be fruitful in learning more about their unique functions.

Deciphering source and sink responses of potato plants (Solanum tuberosum L.) to elevated temperatures

Potato is an important staple food with increasing popularity worldwide. Elevated temperatures significantly impair tuber yield and quality. Breeding heat-tolerant cultivars is therefore an urgent need to ensure sustainable potato production in the future. An integrated approach combining physiology, biochemistry, and molecular biology was undertaken to contribute to a better understanding of heat effects on source- (leaves) and sink-organs (tubers) in a heat-susceptible cultivar. An experimental set-up was designed allowing tissue-specific heat application. Elevated day and night (29°C/27°C) temperatures impaired photosynthesis and assimilate production. Biomass allocation shifted away from tubers towards leaves indicating reduced sink strength of developing tubers. Reduced sink strength of tubers was paralleled by decreased sucrose synthase activity and expression under elevated temperatures. Heat-mediated inhibition of tuber growth coincided with a decreased expression of the phloem-mobile tuberization signal SP6A in leaves. SP6A expression and photosynthesis were also affected, when only the belowground space was heated, and leaves were kept under control conditions. By contrast, the negative effects on tuber metabolism were attenuated, when only the shoot was subjected to elevated temperatures. This, together with transcriptional changes discussed, indicated a bidirectional communication between leaves and tubers to adjust the source capacity and/or sink strength to environmental conditions.

Genetic Loci Conferring Reducing Sugar Accumulation and Conversion of Cold-Stored Potato Tubers Revealed by QTL Analysis in a Diploid Population

Cold-induced sweetening (CIS) caused by reducing sugar (RS) accumulation during storage in low temperature in potato tubers is a critical factor influencing the quality of fried potato products. The reconditioning (REC) by arising storage temperature is a common measure to lower down RS. However, both CIS and REC are genotype-dependent and the genetic basis remains uncertain. In the present study, with a diploid potato population with broad genetic background, four reproducible QTL of CIS and two of REC were resolved on chromosomes 5, 6, and 7 of the CIS-sensitive parent and chromosomes 5 and 11 of the CIS-resistant parent, respectively, implying that these two traits may be genetically independent. This hypothesis was also supported by the colocalization of two functional genes, a starch synthesis gene AGPS2 mapped in QTL CIS_E_07-1 and a starch hydrolysis gene GWD colocated with QTL REC_B_05-1. The cumulative effects of identified QTL were proved to contribute largely and stably to CIS and REC and confirmed with a natural population composed of a range of cultivars and breeding lines. The present research identified reproducible QTL for CIS and REC of potato in diverse conditions and elucidated for the first time their cumulative genetic effects, which provides theoretical bases and applicable means for tuber quality improvement.

Cytosolic glyceraldehyde-3-phosphate dehydrogenases play crucial roles in controlling cold-induced sweetening and apical dominance of potato (Solanum tuberosum L.) tubers

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an important enzyme that functions in producing energy and supplying intermediates for cellular metabolism. Recent researches indicate that GAPDHs have multiple functions beside glycolysis. However, little information is available for functions of GAPDHs in potato. Here, we identified 4 putative cytosolic GAPDH genes in potato genome and demonstrated that the StGAPC1, StGAPC2, and StGAPC3, which are constitutively expressed in potato tissues and cold inducible in tubers, encode active cytosolic GAPDHs. Cosuppression of these 3 GAPC genes resulted in low tuber GAPDH activity, consequently the accumulation of reducing sugars in cold stored tubers by altering the tuber metabolite pool sizes favoring the sucrose pathway. Furthermore, GAPCs-silenced tubers exhibited a loss of apical dominance dependent on cell death of tuber apical bud meristem (TAB-meristem). It was also confirmed that StGAPC1, StGAPC2, and StGAPC3 interacted with the autophagy-related protein 3 (ATG3), implying that the occurrence of cell death in TAB-meristem could be induced by ATG3 associated events. Collectively, the present research evidences first that the GAPC genes play crucial roles in diverse physiological and developmental processes in potato tubers.

Potential impact of genome editing in world agriculture

Changeable biotic and abiotic stress factors that affect crop growth and productivity, alongside a drive to reduce the unintended consequences of plant protection products, will demand highly adaptive farm management practices as well as access to continually improved seed varieties. The former is limited mainly by cost and, in theory, could be implemented in relatively short time frames. The latter is fundamentally a longer-term activity where genome editing can play a major role. The first targets for genome editing will inevitably be loss-of-function alleles, because these are straightforward to generate. In addition, they are likely to focus on traits under simple genetic control and where the results of modification are already well understood from null alleles in existing gene pools or other knockout or silencing approaches such as induced mutations or RNA interference. In the longer term, genome editing will underpin more fundamental changes in agricultural performance and food quality, and ultimately will merge with the tools and philosophies of synthetic biology to underpin and enable new cellular systems, processes and organisms completely. The genetic changes required for simple allele edits or knockout phenotypes are synonymous with those found naturally in conventional breeding material and should be regulated as such. The more radical possibilities in the longer term will need societal engagement along with appropriate safety and ethical oversight.