Expression of auxin synthesis gene tms1 under control of tuber-specific promoter enhances potato tuberization in vitro

Comparative transcriptome analysis of Cyperus esculentus and C. rotundus with contrasting oil contents in tubers defines genes and regulatory networks involved in oil accumulation

Plant vegetative organs present great potential for lipid storage, with tubers of Cyperus esculentus as a unique example. To investigate the genome and transcriptomic features of C. esculentus and related species, we sequenced and assembled the C. esculentus genome at the contig level. Through a comparative study of high-quality transcriptomes across 36 tissues from high-oil and intermediate-oil C. esculentus and low-oil Cyperus rotundus, we identified potential genes and regulatory networks related to tuber oil accumulation. First, we identified tuber-specific genes in two C. esculentus cultivars. Second, genes involved in fatty acid (FA) biosynthesis, triacylglycerol synthesis, and TAG packaging presented increased activity in the later stages of tuber development. Notably, tubers with high oil contents presented higher levels of these genes than those with intermediate oil contents did, whereas tubers with low oil contents presented minimal gene expression. Notably, a large fragment of the FA biosynthesis rate-limiting enzyme-encoding gene BCCP1 was missing from the C. rotundus transcript, which might be responsible for blocking FA biosynthesis in its tubers. WGCNA pinpointed a gene module linked to tuber oil accumulation, with a coexpression network involving the transcription factors WRI1, MYB4, and bHLH68. The ethylene-related genes in this module suggest a role for ethylene signaling in oil accumulation, which is supported by the finding that ethylene (ETH) treatment increases the oil content in C. esculentus tubers. This study identified potential genes and networks associated with tuber oil accumulation in C. esculentus, highlighting the role of specific genes, transcription factors, and ethylene signaling in this process.

Photoperiod and temperature as dominant environmental drivers triggering chemical compositions of garlic bulb during growth

Photoperiod and temperature are crucial for plant growth and development, but the accumulation patterns and regulatory mechanisms of garlic in response to these factors remain unclear. Compared to normal conditions (12/12 h light/dark; 22/15 °C day/night), increasing the photoperiod by 1 h each month with normal temperature (13/11, 14/10, 15/9, 16/8 h; light/dark; 22/15 °C day/night) or increasing photoperiod by 1 h with a 1.5 °C increase in temperature (13/11, 14/10, 15/9, 16/8 h light/dark; 23.5/16, 25/17, 26.5/18, 28/19 °C day/night) at monthly intervals substantially affects garlic growth in early G204, mid-G666, and late G390 harvest cultivars. For both increased photoperiod and temperature, the environment most favorable for bulb growth is characterized by the maximum accumulation of hormones (IAA, JA, and ZT) during bulb formation, while higher levels of ACC, phenolic acids, and organosulfur compounds are observed during the harvesting stage. Furthermore, the accumulation patterns of alliin and allicin in garlic bulbs for G204, G666, and G390 cultivars significantly increased, with fold changes of (2.0, 1.8, and 1.9) and (1.8, 1.7, and 1.5), respectively, in response to increased photoperiod and temperature conditions. Additionally, the accumulation pattern in G204, and G666 was similar but notably distinct from late harvest G390 during growth. In this study, metabolomics models were constructed to assess chemical composition variations and predict the differences among three garlic varieties during the growth stages. These models revealed functional component variations and provided reliable predictions, offering valuable insights for estimating garlic chemical compositions and identifying optimal environmental conditions for growth.

The brassinosteroid receptor StBRI1 promotes tuber development by enhancing plasma membrane H+-ATPase activity in potato

The brassinosteroid (BR) receptor BRASSINOSTEROID-INSENSITIVE 1 (BRI1) plays a critical role in plant growth and development. Although much is known about how BR signaling regulates growth and development in many crop species, the role of StBRI1 in regulating potato (Solanum tuberosum) tuber development is not well understood. To address this question, a series of comprehensive genetic and biochemical methods were applied in this investigation. It was determined that StBRI1 and Solanum tuberosum PLASMA MEMBRANE (PM) PROTON ATPASE2 (PHA2), a PM-localized proton ATPase, play important roles in potato tuber development. The individual overexpression of StBRI1 and PHA2 led to a 22% and 25% increase in tuber yield per plant, respectively. Consistent with the genetic evidence, in vivo interaction analysis using double transgenic lines and PM H+-ATPase activity assays indicated that StBRI1 interacts with the C-terminus of PHA2, which restrains the intramolecular interaction of the PHA2 C-terminus with the PHA2 central loop to attenuate autoinhibition of PM H+-ATPase activity, resulting in increased PHA2 activity. Furthermore, the extent of PM H+-ATPase autoinhibition involving phosphorylation-dependent mechanisms corresponds to phosphorylation of the penultimate Thr residue (Thr-951) in PHA2. These results suggest that StBRI1 phosphorylates PHA2 and enhances its activity, which subsequently promotes tuber development. Altogether, our results uncover a BR-StBRI1-PHA2 module that regulates tuber development and suggest a prospective strategy for improving tuberous crop growth and increasing yield via the cell surface-based BR signaling pathway.

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.

Phenotypic and transcriptomics characterization uncovers genes underlying tuber yield traits and gene expression marker development in potato under aeroponics

MAIN CONCLUSION

Transcriptome analysis in potato varieties revealed genes associated with tuber yield-related traits and developed gene expression markers. This study aimed to identify genes involved in high tuber yield and its component traits in test potato varieties (Kufri Frysona, Kufri Khyati, and Kufri Mohan) compared to control (Kufri Sutlej). The aeroponic evaluation showed significant differences in yield-related traits in the varieties. Total RNA sequencing was performed using tuber and leaf tissues on the Illumina platform. The high-quality reads (QV > 25) mapping with the reference potato genomes revealed statistically significant (P < 0.05) differentially expressed genes (DEGs) into two categories: up-regulated (> 2 Log2 fold change) and down-regulated (< -2 Log2 fold change). DEGs were characterized by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Collectively, we identified genes participating in sugar metabolism, stress response, transcription factors, phytohormones, kinase proteins, and other genes greatly affecting tuber yield and its related traits. A few selected genes were UDP-glucose glucosyltransferase, glutathion S-transferase, GDSL esterase/lipase, transcription factors (MYB, WRKY, bHLH63, and BURP), phytohormones (auxin-induced protein X10A, and GA20 oxidase), kinase proteins (Kunitz-type tuber invertase inhibitor, BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1) and laccase. Based on the selected 17 peptide sequences representing 13 genes, a phylogeny tree and motifs were analyzed. Real time-quantitative polymerase chain reaction (RT-qPCR) analysis was used to validate the RNA-seq results. RT-qPCR based gene expression markers were developed for the genes such as 101 kDa heat shock protein, catechol oxidase B chloroplastic, cysteine protease inhibitor 1, Kunitz-type tuber invertase inhibitor, and laccase to identify high yielding potato genotypes. Thus, our study paved the path for potential genes associated with tuber yield traits in potato under aeroponics.

Nitrogen-Activated CLV3/ESR-Related 4 (CLE4) Regulates Shoot, Root, and Stolon Growth in Potato

In potato, high levels of nitrogen (N) can lead to excessive vegetative growth at the expense of tuber development, resulting in lower yield and poor-quality tubers. We found that Solanum tuberosum CLE4 (StCLE4) is expressed most strongly in the roots grown in N-rich media, and it positively regulates potato root growth under N-deficient conditions. We noted that StCLE4 functions as a negative regulator of normal shoot apex development similar to CLV3 in Arabidopsis. Transcriptomic analysis revealed that overexpression of StCLE4 resulted in the repression of the StIT1 gene, a regulator of potato tuber initiation. StCLE4-overexpressing stolons were converted into branches, that were similar to a mild phenotype of the it1 (identity of tuber 1) mutant. We also found that NIN-like proteins, key regulators of nitrate signaling bind to the regulatory sequence of StIT1 in a yeast one-hybrid assay. Taken together, our findings suggest that StCLE4 regulates shoot, root, and stolon growth in potato.

Canonical and Alternative Auxin Signaling Systems in Mono-, Di-, and Tetraploid Potatoes

It has long been known that the phytohormone auxin plays a promoting role in tuber formation and stress tolerance in potatoes. Our study aimed to identify and characterize the complete sets of auxin-related genes that presumably constitute the entire auxin signaling system in potato (Solanum tuberosum L.). The corresponding genes were retrieved from sequenced genomes of the doubled monoploid S. tuberosum DM1-3-516-R44 (DM) of the Phureja group, the heterozygous diploid line RH89-039-16 (RH), and the autotetraploid cultivar Otava. Both canonical and noncanonical auxin signaling pathways were considered. Phylogenetic and domain analyses of deduced proteins were supplemented by expression profiling and 3D molecular modeling. The canonical and ABP1-mediated pathways of auxin signaling appeared to be well conserved. The total number of potato genes/proteins presumably involved in canonical auxin signaling is 46 and 108 in monoploid DM and tetraploid Otava, respectively. Among the studied potatoes, spectra of expressed genes obviously associated with auxin signaling were partly cultivar-specific and quite different from analogous spectrum in Arabidopsis. Most of the noncanonical pathways found in Arabidopsis appeared to have low probability in potato. This was equally true for all cultivars used irrespective of their ploidy. Thus, some important features of the (noncanonical) auxin signaling pathways may be variable and species-specific.

CRISPR/Cas genome editing system and its application in potato

Potato is the largest non-cereal food crop worldwide and a vital substitute for cereal crops, considering its high yield and great nutritive value. It plays an important role in food security. The CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated) system has the advantages of easy operation, high efficiency, and low cost, which shows a potential in potato breeding. In this paper, the action mechanism and derivative types of the CRISPR/Cas system and the application of the CRISPR/Cas system in improving the quality and resistance of potatoes, as well as overcoming the self-incompatibility of potatoes, are reviewed in detail. At the same time, the application of the CRISPR/Cas system in the future development of the potato industry was analyzed and prospected.

Modifications of Phytohormone Metabolism Aimed at Stimulation of Plant Growth, Improving Their Productivity and Tolerance to Abiotic and Biotic Stress Factors

Due to the growing human population, the increase in crop yield is an important challenge for modern agriculture. As abiotic and biotic stresses cause severe losses in agriculture, it is also crucial to obtain varieties that are more tolerant to these factors. In the past, traditional breeding methods were used to obtain new varieties displaying demanded traits. Nowadays, genetic engineering is another available tool. An important direction of the research on genetically modified plants concerns the modification of phytohormone metabolism. This review summarizes the state-of-the-art research concerning the modulation of phytohormone content aimed at the stimulation of plant growth and the improvement of stress tolerance. It aims to provide a useful basis for developing new strategies for crop yield improvement by genetic engineering of phytohormone metabolism.

Recent Advances in Molecular Improvement for Potato Tuber Traits

Potato is an important crop due to its nutritional value and high yield potential. Improving the quality and quantity of tubers remains one of the most important breeding objectives. Genetic mapping helps to identify suitable markers for use in the molecular breeding, and combined with transgenic approaches provides an efficient way for gaining desirable traits. The advanced plant breeding tools and molecular techniques, e.g., TALENS, CRISPR-Cas9, RNAi, and cisgenesis, have been successfully used to improve the yield and nutritional value of potatoes in an increasing world population scenario. The emerging methods like genome editing tools can avoid incorporating transgene to keep the food more secure. Multiple success cases have been documented in genome editing literature. Recent advances in potato breeding and transgenic approaches to improve tuber quality and quantity have been summarized in this review.

Integrative omics approaches revealed a crosstalk among phytohormones during tuberous root development in cassava

Integrative omics approaches revealed a crosstalk among phytohormones during tuberous root development in cassava. Tuberous root formation is a complex process consisting of phase changes as well as cell division and elongation for radial growth. We performed an integrated analysis to clarify the relationships among metabolites, phytohormones, and gene transcription during tuberous root formation in cassava (Manihot esculenta Crantz). We also confirmed the effects of the auxin (AUX), cytokinin (CK), abscisic acid (ABA), jasmonic acid (JA), gibberellin (GA), brassinosteroid (BR), salicylic acid, and indole-3-acetic acid conjugated with aspartic acid on tuberous root development. An integrated analysis of metabolites and gene expression indicated the expression levels of several genes encoding enzymes involved in starch biosynthesis and sucrose metabolism are up-regulated during tuberous root development, which is consistent with the accumulation of starch, sugar phosphates, and nucleotides. An integrated analysis of phytohormones and gene transcripts revealed a relationship among AUX signaling, CK signaling, and BR signaling, with AUX, CK, and BR inducing tuberous root development. In contrast, ABA and JA inhibited tuberous root development. These phenomena might represent the differences between stem tubers (e.g., potato) and root tubers (e.g., cassava). On the basis of these results, a phytohormonal regulatory model for tuberous root development was constructed. This model may be useful for future phytohormonal studies involving cassava.

Tuber and Tuberous Root Development

Root and tuber crops have been an important part of human nutrition since the early days of humanity, providing us with essential carbohydrates, proteins, and vitamins. Today, they are especially important in tropical and subtropical regions of the world, where they help to feed an ever-growing population. Early induction and storage organ size are important agricultural traits, as they determine yield over time. During potato tuberization, environmental and metabolic status are sensed, ensuring proper timing of tuberization mediated by phloem-mobile signals. Coordinated cellular restructuring and expansion growth, as well as controlled storage metabolism in the tuber, are executed. This review summarizes our current understanding of potato tuber development and highlights similarities and differences to important tuberous root crop species like sweetpotato and cassava. Finally, we point out knowledge gaps that need to be filled before a complete picture of storage organ development can emerge.

Auxin: An emerging regulator of tuber and storage root development

Many tuber and storage root crops owing to their high nutritional values offer high potential to overcome food security issues. The lack of information regarding molecular mechanisms that govern belowground storage organ development (except a tuber crop, potato) has limited the application of biotechnological strategies for improving storage crop yield. Phytohormones like gibberellin and cytokinin are known to play a crucial role in governing potato tuber development. Another phytohormone, auxin has been shown to induce tuber initiation and growth, and its crosstalk with gibberellin and strigolactone in a belowground modified stem (stolon) contributes to the overall potato tuber yield. In this review, we describe the crucial role of auxin biology in development of potato tubers. Considering the emerging reports from commercially important storage root crops (sweet potato, cassava, carrot, sugar beet and radish), we propose the function of auxin and related gene regulatory network in storage root development. The pattern of auxin content of stolon during various stages of potato tuber formation appears to be consistent with its level in various developmental stages of storage roots. We have also put-forward the potential of three-way interaction between auxin, strigolactone and mycorrhizal fungi in tuber and storage root development. Overall, we propose that auxin gene regulatory network and its crosstalk with other phytohormones in stolons/roots could govern belowground tuber and storage root development.

Gene Expression Analysis of Microtubers of Potato Solanum tuberosum L. Induced in Cytokinin Containing Medium and Osmotic Stress

Potato microtuber productions through in vitro techniques are ideal propagules for producing high quality seed potatoes. Microtuber development is influenced by several factors, i.e., high content sucrose and cytokinins are among them. To understand a molecular mechanism of microtuberization using osmotic stress and cytokinin signaling will help us to elucidate this process. We demonstrate in this work a rapid and efficient protocol for microtuber development and gene expression analysis. Medium with high content of sucrose and gelrite supplemented with 2iP as cytokinin under darkness condition produced the higher quantity and quality of microtubers. Gene expression analysis of genes involved in the two-component signaling system (StHK1), cytokinin signaling, (StHK3, StHP4, StRR1) homeodomains (WUSCHEL, POTH1, BEL5), auxin signaling, ARF5, carbon metabolism (TPI, TIM), protein synthesis, NAC5 and a morphogenetic regulator of tuberization (POTH15) was performed by qPCR real time. Differential gene expression was observed during microtuber development. Gene regulation of two component and cytokinin signaling is taking place during this developmental process, yielding more microtubers. Further analysis of each component is required to elucidate it.

Global View on the Cytokinin Regulatory System in Potato

Cytokinins (CKs) were earlier shown to promote potato tuberization. Our study aimed to identify and characterize CK-related genes which constitute CK regulatory system in the core potato (Solanum tuberosum) genome. For that, CK-related genes were retrieved from the sequenced genome of the S. tuberosum doubled monoploid (DM) Phureja group, classified and compared with Arabidopsis orthologs. Analysis of selected gene expression was performed with a transcriptome database for the S. tuberosum heterozygous diploid line RH89-039-16. Genes responsible for CK signaling, biosynthesis, transport, and metabolism were categorized in an organ-specific fashion. According to this database, CK receptors StHK2/3 predominate in leaves and flowers, StHK4 in roots. Among phosphotransmitters, StHP1a expression largely predominates. Surprisingly, two pseudo-phosphotransmitters intended to suppress CK effects are hardly expressed in studied organs. Among B-type RR genes, StRR1b, StRR11, and StRR18a are actively expressed, with StRR1b expressing most uniformly in all organs and StRR11 exhibiting the highest expression in roots. By cluster analysis four types of prevailing CK-signaling chains were identified in (1) leaves and flowers, StHK2/3→S t H P1a→StRR1b/+; (2) shoot apical meristems, stolons, and mature tubers, StHK2/4→S t H P1a→StRR1b/+; (3) stems and young tubers, StHK2/4→S t H P1a→StRR1b/11/18a; and (4) roots and tuber sprouts, StHK4→S t H P1a→StRR11/18a. CK synthesis genes StIPT3/5 and StCYP735A are expressed mainly in roots followed by tuber sprouts, but rather weakly in stolons and tubers. By contrast, CK-activation genes StLOGs are active in stolons, and StLOG3b expression is even stolon-confined. Apparently, the main CK effects on tuber initiation are realized via activity of StLOG1/3a/3b/7c/8a genes in stolons. Current advances and future directions in potato research are discussed.

Endogenous levels of cytokinins, indole-3-acetic acid and abscisic acid in in vitro grown potato: A contribution to potato hormonomics

A number of scientific reports published to date contain data on endogenous levels of various phytohormones in potato (Solanum tuberosum L.) but a complete cytokinin profile of potato tissues, that would include data on all particular molecular forms of cytokinin, has still been missing. In this work, endogenous levels of all analytically detectable isoprenoid cytokinins, as well as the auxin indole-3-acetic acid (IAA), and abscisic acid (ABA) have been determined in shoots and roots of 30 day old in vitro grown potato (cv. Désirée). The results presented here are generally similar to other data reported for in vitro grown potato plants, whereas greenhouse-grown plants typically contain lower levels of ABA, possibly indicating that in vitro grown potato is exposed to chronic stress. Cytokinin N-glucosides, particularly N7-glucosides, are the dominant cytokinin forms in both shoots and roots of potato, whereas nucleobases, as the bioactive forms of cytokinins, comprise a low proportion of cytokinin levels in tissues of potato. Differences in phytohormone composition between shoots and roots of potato suggest specific patterns of transport and/or differences in tissue-specific metabolism of plant hormones. These results represent a contribution to understanding the hormonomics of potato, a crop species of extraordinary economic importance.

Auxins in potato: molecular aspects and emerging roles in tuber formation and stress resistance

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

Target genes for plant productivity improvement

The use of chemical fertilizers and pesticides, as well as the development of high-yielding varieties enabled substantial increase in crop productivity during the 20th century. However, the increase in yield over the last two decades has been slower. It is thought that further improvement in productivity of the major crop species using traditional cultivation methods is limited. Therefore, the use of genetic engineering seems to be a promising approach. There is ongoing research concerning genes that have an impact on plant growth, development and yield. The proteins and miRNAs encoded by these genes participate in a variety of processes, such as growth regulation, assimilate transport and partitioning as well as macronutrient uptake and metabolism. This paper presents the major directions in research concerning genes that may be targets of genetic engineering aimed to improve plant productivity.

Phytohormones as targets for improving plant productivity and stress tolerance

In this review, we summarize the results of experiments that lead to altered levels of phytohormones in transgenic plants to improve plant productivity. The available data indicate that manipulating the level of phytohormones might also be a promising way to enhance the environmental stress tolerance of crop plants. In the regulation of the level of phytohormones, both biosynthesis and their catabolism pathways can be targeted for engineering purposes. Moreover, the signaling pathways of phytohormones should explored in this respect. In genetic modifications, conditional promoters must be developed to avoid undesired effects on growth. In order to find a practical application, the effects of genetic modifications should be further verified under field conditions and over a longer time scale.

Cytokinin perception in potato: new features of canonical players

Potato is the most economically important non-cereal food crop. Tuber formation in potato is regulated by phytohormones, cytokinins (CKs) in particular. The present work studied CK signal perception in potato. The sequenced potato genome of doubled monoploid Phureja was used for bioinformatic analysis and as a tool for identification of putative CK receptors from autotetraploid potato cv. Désirée. All basic elements of multistep phosphorelay required for CK signal transduction were identified in the Phureja genome, including three genes orthologous to three CK receptor genes (AHK 2-4) of Arabidopsis. As distinct from Phureja, autotetraploid potato contains at least two allelic isoforms of each receptor type. Putative receptor genes from Désirée plants were cloned, sequenced and expressed, and the main characteristics of encoded proteins were determined, in particular their consensus motifs, modelled structure, ligand-binding properties, and ability to transmit CK signals. In all studied aspects the predicted sensor histidine kinases met the requirements for genuine CK receptors. Expression of potato CK receptors was found to be organ-specific and sensitive to growth conditions, particularly to sucrose content. Our results provide a solid basis for further in-depth study of CK signaling system and biotechnological improvement of potato.

Core features of the hormonal status in in vitro grown potato plants

Some time ago, potato transformants expressing Agrobacterium-derived auxin synthesis gene tms1 were generated. These tms1-transgenic plants, showing enhanced productivity, were studied for their hormonal status, turnover and responses in comparison with control plants. For this purpose, contents of phytohormones belonging to six different classes (auxins, cytokinins, gibberellins, abscisic, jasmonic and salicylic acids) were determined by a sensitive UPLC-MS/MS method in tubers and shoots of in vitro grown plants. To date, this study represents the most comprehensive analysis of the potato hormonal system. On the basis of obtained results, several new generalizations concerning potato hormonal status were drawn. Overall, these data can serve as a framework for forthcoming integrative studies of the hormonal system in potato plants.

Reduction of indole-3-acetic acid methyltransferase activity compensates for high-temperature male sterility in Arabidopsis

High temperature is a general stress factor that causes a decrease in crop yield. It has been shown that auxin application reduces the male sterility caused by exposure to higher temperatures. However, widespread application of a hormone with vast effects on plant physiology may be discouraged in many cases. Therefore, the generation of new plant varieties that locally enhance auxin in reproductive organs may represent an alternative strategy. We have explored the possibility of increasing indole-3-acetic acid (IAA) in ovaries by reducing IAA methyltransferase1 (IAMT1) activity in Arabidopsis thaliana. The iamt1 mutant showed increased auxin signalling in funiculi, which correlated with a higher growth rate of wild-type pollen in contact with mutant ovaries and premature ovule fertilization. While the production of seeds per fruit was similar in the wild type and the mutant at 20 °C, exposure to 29 °C caused a more severe decrease in fertility in the wild type than in the mutant. Loss of IAMT1 activity was also associated with the production of more nodes after flowering and higher tolerance of the shoot apical meristem to higher temperatures. As a consequence, the productivity of the iamt1 mutant under higher temperatures was more than double of that of the wild type, with almost no apparent trade-off.

The plasma membrane H+-ATPase gene family in Solanum tuberosum L. Role of PHA1 in tuberization

This study presents the characterization of the plasma membrane (PM) H+-ATPases in potato, focusing on their role in stolon and tuber development. Seven PM H+-ATPase genes were identified in the Solanum tuberosum genome, designated PHA1-PHA7. PHA genes show distinct expression patterns in different plant tissues and under different stress treatments. Application of PM H+-ATPase inhibitors arrests stolon growth, promotes tuber induction, and reduces tuber size, indicating that PM H+-ATPases are involved in tuberization, acting at different stages of the process. Transgenic potato plants overexpressing PHA1 were generated (PHA1-OE). At early developmental stages, PHA1-OE stolons elongate faster and show longer epidermal cells than wild-type stolons; this accelerated growth is accompanied by higher cell wall invertase activity, lower starch content, and higher expression of the sucrose-H+ symporter gene StSUT1. PHA1-OE stolons display an increased branching phenotype and develop larger tubers. PHA1-OE plants are taller and also present a highly branched phenotype. These results reveal a prominent role for PHA1 in plant growth and development. Regarding tuberization, PHA1 promotes stolon elongation at early stages, and tuber growth later on. PHA1 is involved in the sucrose-starch metabolism in stolons, possibly providing the driving force for sugar transporters to maintain the apoplastic sucrose transport during elongation.

Auxin synthesis gene tms1 driven by tuber-specific promoter alters hormonal status of transgenic potato plants and their responses to exogenous phytohormones

Ectopic auxin overproduction in transgenic potato leads to enhanced productivity accompanied with concerted and occasional changes in hormonal status, and causing altered response of transformants to exogenous auxin or cytokinin. Previously, we generated potato transformants expressing Agrobacterium-derived auxin synthesis gene tms1 driven by tuber-specific patatin gene promoter (B33-promoter). Here, we studied the endogenous hormonal status and the response to exogenous phytohormones in tms1 transformants cultured in vitro. Adding indole-3-acetic acid (IAA) or kinetin to culture medium affected differently tuberization of tms1-transformed and control plants, depending also on sucrose content in the medium. Exogenous phytohormones ceased to stimulate the tuber initiation in transformants at high (5-8%) sucrose concentration, while in control plants the stimulation was observed in all experimental settings. Furthermore, exogenous auxin partly inhibited the tuber initiation, and exogenous cytokinin reduced the average tuber weight in most transformants at high sucrose content. The elevated auxin level in tubers of the transformants was accompanied with a decrease in content of cytokinin bases and their ribosides in tubers and most shoots. No concerted changes in contents of abscisic, jasmonic, salicylic acids and gibberellins in tubers were detected. The data on hormonal status indicated that the enhanced productivity of tms1 transformants was due to auxin and not mediated by other phytohormones. In addition, exogenous cytokinin was shown to upregulate the expression of genes encoding orthologs of auxin receptors. Overall, the results showed that tms1 expression and local increase in IAA level in transformants affect both the balance of endogenous cytokinins and the dynamics of tuberization in response to exogenous hormones (auxin, cytokinin), the latter reaction depending also on the carbohydrate supply. We introduce a basic model for the hormonal network controlling tuberization.

Multiple Mobile mRNA Signals Regulate Tuber Development in Potato

Included among the many signals that traffic through the sieve element system are full-length mRNAs that function to respond to the environment and to regulate development. In potato, several mRNAs that encode transcription factors from the three-amino-loop-extension (TALE) superfamily move from leaves to roots and stolons via the phloem to control growth and signal the onset of tuber formation. This RNA transport is enhanced by short-day conditions and is facilitated by RNA-binding proteins from the polypyrimidine tract-binding family of proteins. Regulation of growth is mediated by three mobile mRNAs that arise from vasculature in the leaf. One mRNA, StBEL5, functions to activate growth, whereas two other, sequence-related StBEL's, StBEL11 and StBEL29, function antagonistically to repress StBEL5 target genes involved in promoting tuber development. This dynamic system utilizes closely-linked phloem-mobile mRNAs to control growth in developing potato tubers. In creating a complex signaling pathway, potato has evolved a long-distance transport system that regulates underground organ development through closely-associated, full-length mRNAs that function as either activators or repressors.

The protein phosphatase 2A catalytic subunit StPP2Ac2b acts as a positive regulator of tuberization induction in Solanum tuberosum L

This study provides the first genetic evidence for the role of PP2A in tuberization, demonstrating that the catalytic subunit StPP2Ac2b positively modulates tuber induction, and that its function is related to the regulation of gibberellic acid metabolism. The results contribute to a better understanding of the molecular mechanism controlling tuberization induction, which remains largely unknown. The serine/threonine protein phosphatases type 2A (PP2A) are implicated in several physiological processes in plants, playing important roles in hormone responses. In cultivated potato (Solanum tuberosum), six PP2A catalytic subunits (StPP2Ac) were identified. The PP2Ac of the subfamily I (StPP2Ac1, 2a and 2b) were suggested to be involved in the tuberization signaling in leaves, where the environmental and hormonal signals are perceived and integrated. The aim of this study was to investigate the role of PP2A in the tuberization induction in stolons. We selected one of the catalytic subunits of the subfamily I, StPP2Ac2b, to develop transgenic plants overexpressing this gene (StPP2Ac2b-OE). Stolons from StPP2Ac2b-OE plants show higher tuber induction rates in vitro, as compared to wild type stolons, with no differences in the number of tubers obtained at the end of the process. This effect is accompanied by higher expression levels of the gibberellic acid (GA) catabolic enzyme StGA2ox1. GA up-regulates StPP2Ac2b expression in stolons, possibly as part of the feedback system by which the hormone regulates its own level. Sucrose, a tuber-promoting factor in vitro, increases StPP2Ac2b expression. We conclude that StPP2Ac2b acts in stolons as a positive regulator tuber induction, integrating different tuberization-related signals mainly though the modulation of GA metabolism.

Key players associated with tuberization in potato: potential candidates for genetic engineering

Tuberization in potato (Solanum tuberosum L.) is a complex biological phenomenon which is affected by several environmental cues, genetic factors and plant nutrition. Understanding the regulation of tuber induction is essential to devise strategies to improve tuber yield and quality. It is well established that short-day photoperiods promote tuberization, whereas long days and high-temperatures inhibit or delay tuberization. Worldwide research on this complex biological process has yielded information on the important bio-molecules (proteins, RNAs, plant growth regulators) associated with the tuberization process in potato. Key proteins involved in the regulation of tuberization include StSP6A, POTH1, StBEL5, StPHYB, StCONSTANS, Sucrose transporter StSUT4, StSP5G, etc. Biomolecules that become transported from "source to sink" have also been suggested to be important signaling candidates regulating the tuberization process in potatos. Four molecules, namely StSP6A protein, StBEL5 RNA, miR172 and GAs, have been found to be the main candidates acting as mobile signals for tuberization. These biomolecules can be manipulated (overexpressed/inhibited) for improving the tuberization in commercial varieties/cultivars of potato. In this review, information about the genes/proteins and their mechanism of action associated with the tuberization process is discussed.

Genome-wide survey and expression analysis of the amino acid transporter superfamily in potato (Solanum tuberosum L.)

Amino acid transporters (AATs) are integral membrane proteins responsible for the transmembrane transport of amino acids and play important roles in various physiological processes of plants. However, there has not yet been a genome-wide overview of the StAAT gene family to date and only StAAP1 has been previously studied in potato. In this paper, a total of 72 StAATs were identified using a series of bioinformatics searches and classified into 12 subfamilies based on their phylogenetic relationship with known Arabidopsis and rice AATs. Chromosomal localization revealed their distribution on all 12 chromosomes. Nearly one-third of StAAT genes (23 of 72) were derived from gene duplication, among which tandem duplication made the greatest contribution to the expansion of the StAAT family. Motif analysis showed that the same subfamily had similar conserved motifs in both numbers and varieties. Moreover, high-throughput sequencing data was used to analyze the expression patterns of StAAT genes and was verified by quantitative real-time RT-PCR. The expression of StAAT genes exhibited both abundant and tissue-specific expression patterns, which might be connected to their functional roles in long- and short-distance transport. This study provided a comprehensive survey of the StAAT gene family, and could serve as a theoretical foundation for the further functional identification and utilization of family members.

Principales promotores utilizados en la transformación genética de plantas

El conocimiento pleno de los promotores determina el éxito en la obtención de nuevos cultivares de plantas a través de técnicas biotecnológicas, ya que dicha secuencia del ADN regula la transcripción de otras regiones adyacentes o cercanas, encontrándose los siguientes promotores: constitutivos, tejido-específicos o estadio-específicos, inducibles y sintéticos. En esta revisión se resume de manera precisa los conceptos, ventajas y limitaciones de los distintos tipos de promotores, con ejemplos claros de ello.Palabras clave: promotor, biotecnología vegetal, transcripción genética.

Genome-wide survey of Aux/IAA gene family members in potato (Solanum tuberosum): Identification, expression analysis, and evaluation of their roles in tuber development

The Auxin/indole-3-acetic acid (Aux/IAA) genes encode short-lived nuclear proteins that are known to be involved in the primary cellular responses to auxin. To date, systematic analysis of the Aux/IAA genes in potato (Solanum tuberosum) has not been conducted. In this study, a total of 26 potato Aux/IAA genes were identified (designated from StIAA1 to StIAA26), and the distribution of four conserved domains shared by the StIAAs were analyzed based on multiple sequence alignment and a motif-based sequence analysis. A phylogenetic analysis of the Aux/IAA gene families of potato and Arabidopsis was also conducted. In order to assess the roles of StIAA genes in tuber development, the results of RNA-seq studies were reformatted to analyze the expression patterns of StIAA genes, and then verified by quantitative real-time PCR. A large number of StIAA genes (12 genes) were highly expressed in stolon organs and in during the tuber initiation and expansion developmental stages, and most of these genes were responsive to indoleacetic acid treatment. Our results suggested that StIAA genes were involved in the process of tuber development and provided insights into functional roles of potato Aux/IAA genes.