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Contains fulltext : 226781.pdf (publisher's version ) (Open Access)

Contains fulltext : 226781.pdf (publisher's version ) (Open Access)

Contains fulltext : 226781.pdf (publisher's version ) (Open Access)

One of the major global challenges of today is to meet the food demands of an ever increasing population (food demand will increase by 50% in 2030). One approach to address this challenge is to breed new crop varieties that yield more even under unfavorable conditions e.g. have improved tolerance to drought and/or resistance to pathogens. However, designing a breeding program is a laborious and time consuming effort that often lacks the capacity to generate new cultivars quickly in response to the required traits. Recent advances in biotechnology and genomics data science have the potential to accelerate and precise breeding programs greatly. As large-scale genomic data sets for crop species are available in multiple independent data sources and scientific literature, this thesis provides innovative technologies that use natural language processing (NLP) and semantic web technologies to address challenges of integrating genomic data for improving plant breeding. Firstly, in this research study, we developed a supervised Natural language processing (NLP) model with the help of IBM Watson, to extract knowledge networks containing genotypic-phenotypic associations of potato tuber flesh color from the scientific literature. Secondly, a table mining tool called QTLTableMiner++ (QTM) was developed which enables knowledge discovery of novel genomic regions (such as QTL regions), which positively or negatively affect the traits of interest. The objective of both above mentioned, NLP techniques was to extract information which is implicitly described in the literature and is not available in structured resources, like databases. Thirdly, with the help of semantic web technology, a linked-data platform called Solanaceae linked data platform(pbg-ld) was developed, to semantically integrates geno- and pheno-typic data of Solanaceae species. This platform combines both unstructured data from scientific literature and structured data from publicly available biological databases u

Potato plants reproduce sexually through the formation of flowers, berries and seeds, and asexually through the formation of tubers. Environmental conditions can be used as a flexible switch to control reproduction in potato, steering it towards flowering when seeds are required for breeding or propagation, or towards tuberization when tubers are required for propagation or potato production. Light is a convenient environmental switch, as spectrum, photoperiod, light intensity and the daily light integral (DLI) can be manipulated. In this thesis the effect of light on tuberization and flowering time was quantified and the underlying molecular regulation was explored. Finally it was determined if tuberization and flowering compete and if so, how this is regulated. Tuberization is a short-day process. In long days, tuberization is delayed or even inhibited (depending on the genotype). In this thesis it was determined whether an external coincidence model can explain the photoperiodic effect on tuberization in potato. In the model plant Arabidopsis, photoperiodic flowering is controlled by coincidence of light and CONSTANS (CO) expression. In potato, a similar model was hypothesized to explain photoperiodic tuberization. Coincidence of the potato CO (StCOL1) expression and light in long days would induce StSP5G, which in turn would lead to the inhibition of StSP6A, the gene encoding for the tuberization signal StSP6A. Thus coincidence of StCOL1 and light is expected to repress tuberization. By using night breaks (30 minutes of light applied in the night) that coincided with StCOL1 expression in the night or not, it was demonstrated that coincidence between light and StCOL1 expression does not necessarily repress tuberization. In addition, it was shown that although flower bud appearance time is not affected by photoperiod, the number of leaves formed before the inflorescence in the genotype S. andigena decreases under shorter photoperiods, indicating an effect of photo

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

Potato plants form tuberous storage organs on underground modified stems called stolons. Tubers are rich in starch, proteins, and other important nutrients, making potato one of the most important staple food crops. The timing of tuber development in wild potato is regulated by day length through a mechanism that is closely related to floral transition [1, 2]. Tuberization is also known to be regulated by the availability of assimilates, in particular sucrose, the transported form of sugar, required for starch synthesis. During the onset of tuber development, the mode of sucrose unloading switches from apoplastic to symplastic [3]. Here, we show that this switch may be mediated by the interaction between the tuberization-specific FT homolog StSP6A and the sucrose efflux transporter StSWEET11 [4]. The binding of StSP6A to StSWEET11 blocked the leakage of sucrose to the apoplast, and is therefore likely to promote symplastic sucrose transport. The direct physical interaction between StSWEET11 and StSP6A proteins represents a link between the sugar and photoperiodic pathways for the regulation of potato tuber formation. Our data suggest that a previously undiscovered function for the FT family of proteins extends their role as mobile signals to mediators of source-sink partitioning, opening the possibility for modifying source-sink interactions.

Background In flowering plants it has been shown that de novo genome assemblies of different species and genera show a significant drop in the proportion of alignable sequence. Within a plant species, however, it is assumed that different haplotypes of the same chromosome align well. In this paper we have compared three de novo assemblies of potato chromosome 5 and report on the sequence variation and the proportion of sequence that can be aligned. Results For the diploid potato clone RH89-039-16 (RH) we produced two linkage phase controlled and haplotype-specific assemblies of chromosome 5 based on BAC-by-BAC sequencing, which were aligned to each other and compared to the 52 Mb chromosome 5 reference sequence of the doubled monoploid clone DM 1–3 516 R44 (DM). We identified 17.0 Mb of non-redundant sequence scaffolds derived from euchromatic regions of RH and 38.4 Mb from the pericentromeric heterochromatin. For 32.7 Mb of the RH sequences the correct position and order on chromosome 5 was determined, using genetic markers, fluorescence in situ hybridisation and alignment to the DM reference genome. This ordered fraction of the RH sequences is situated in the euchromatic arms and in the heterochromatin borders. In the euchromatic regions, the sequence collinearity between the three chromosomal homologs is good, but interruption of collinearity occurs at nine gene clusters. Towards and into the heterochromatin borders, absence of collinearity due to structural variation was more extensive and was caused by hemizygous and poorly aligning regions of up to 450 kb in length. In the most central heterochromatin, a total of 22.7 Mb sequence from both RH haplotypes remained unordered. These RH sequences have very few syntenic regions and represent a non-alignable region between the RH and DM heterochromatin haplotypes of chromosome 5. Conclusions Our results show that among homologous potato chromosomes large regions are present with dramatic loss of sequence collinearity

This paper describes the progress that has been made since the draft genome sequence of potato has been obtained and the analyses that need to be done to make further progress. Although sequencing has become less expensive and read lengths have increased, making optimal use of the information obtained is still difficult, certainly in the tetraploid potato crop. Major challenges in potato genomics are standardized genome assembly and haplotype analysis. Sequencing methods need to be improved further to achieve precision breeding. With the current new generation sequencing technology, the focus in potato breeding will shift from phenotype improvement to genotype improvement. In this respect, it is essential to realize that different alleles of the same gene can lead to different phenotypes depending on the genetic background and that there is significant epistatic interaction between different alleles. Genome-wide association studies will gain statistical power when binary single nucleotide polymorphism (SNP) data can be replaced with multi-allelic haplotype data. Binary SNP can be distributed across the many different alleles per locus or may be haplotype-specific, and potentially tag specific alleles which clearly differ in their contribution to a certain trait value. Assembling reads from the same linkage phase proved to allow constructing sufficiently long haplotype tracts to ensure their uniqueness. Combining large phenotyping data sets with modern approaches to sequencing and haplotype analysis and proper software will allow the efficiency of potato breeding to increase.

The PIN family of trans-membrane proteins mediates auxin efflux throughout the plant and during various phases of plant development. In Arabidopsis thaliana, the PIN family comprised of 8 members, divided into ‘short’ and ‘long’ PINs according to the length of the hydrophilic domain of the protein. Based on sequence homology using the recently published potato genome sequence (Solanum tuberosum group Phureja) we identified ten annotated potato StPIN genes. Mining the publicly available gene expression data, we constructed a catalogue tissue specificity of StPIN gene expression, focusing on the process of tuberization. A total of four StPIN genes exhibited increased expression four days after tuber induction, prior to the onset of stolon swelling. For two PIN genes, StPIN4 and StPIN2, promoter sequences were cloned and fused to the GUS reporter protein to study tissue specificity in more detail. StPIN4 promoter driven GUS staining was detected in the flower stigma, in the flower style, below the ovary and petals, in the root tips, in the vascular tissue of the stolons and in the tuber parenchyma cells. StPIN2 promoter driven GUS staining was detected in flower buds, in the vascular tissue of the swelling stolons and in the storage parenchyma of the growing tubers. Based on our results, we postulate a role for the StPINs in redistributing auxin in the swelling stolon during early events in tuber development.

The genome of potato, a major global food crop, was recently sequenced. The work presented here details the integration of the potato reference genome (DM) with a new STS marker based linkage map and other physical and genetic maps of potato and the closely related species tomato. Primary anchoring of the DM genome assembly was accomplished using a diploid segregating population, which was genotyped with several types of molecular genetic markers to construct a new ~936 cM linkage map comprising 2,469 marker loci. In silico anchoring approaches employed genetic and physical maps from the diploid potato genotype RH and tomato. This combined approach has allowed 951 superscaffolds to be ordered into pseudomolecules corresponding to the 12 potato chromosomes. These pseudomolecules represent 674 Mb (~93%) of the 723 Mb genome assembly and 37,482 (~96%) of the 39,031 predicted genes. The superscaffold order and orientation within the pseudomolecules is closely collinear with independently constructed high density linkage maps. Comparisons between marker distribution and physical location reveal regions of greater and lesser recombination, as well as regions exhibiting significant segregation distortion. The work presented here has led to a greatly improved ordering of the potato reference genome superscaffolds into chromosomal 'pseudomolecules'.

Nu het aardappelgenoom in kaart is gebracht, kan het werk eigenlijk pas goed beginnen. ‘We kunnen doelgerichter zoeken naar genen die betrokken zijn bij resistenties en kwaliteit.’ En naar waarom de aardappel knollen vormt en zijn zusje de tomaat niet.

Background With the completion of genome sequences belonging to some of the major crop plants, new challenges arise to utilize this data for crop improvement and increased food security. The field of genetical genomics has the potential to identify genes displaying heritable differential expression associated to important phenotypic traits. Here we describe the identification of expression QTLs (eQTLs) in two different potato tissues of a segregating potato population and query the potato genome sequence to differentiate between cis- and trans-acting eQTLs in relation to gene subfunctionalization. Results Leaf and tuber samples were analysed and screened for the presence of conserved and tissue dependent eQTLs. Expression QTLs present in both tissues are predominantly cis-acting whilst for tissue specific QTLs, the percentage of trans-acting QTLs increases. Tissue dependent eQTLs were assigned to functional classes and visualized in metabolic pathways. We identified a potential regulatory network on chromosome 10 involving genes crucial for maintaining circadian rhythms and controlling clock output genes. In addition, we show that the type of genetic material screened and sampling strategy applied, can have a high impact on the output of genetical genomics studies. Conclusions Identification of tissue dependent regulatory networks based on mapped differential expression not only gives us insight in tissue dependent gene subfunctionalization but brings new insights into key biological processes and delivers targets for future haplotyping and genetic marker development.

To understand the molecular basis of potato starch related traits and the underlying starch biosynthesis and degradation, a Quantitative Trait Locus (QTL) analysis in combination with a candidate gene approach was performed. The diploid mapping population C × E, consisting of 249 individuals, was assayed over two consecutive years, for chipping colour, cold induced sweetening, starch content, starch granule size, starch gelling temperature, starch enthalpy, amylose content and degree of starch phosphorylation. QTLs were observed for all traits, except enthalpy on eight out of the twelve potato chromosomes. Several QTLs were found to be consistent over 2 years. Clustering of co-localizing QTLs was observed on some chromosomes, indicating common genetic factors for the different traits. On chromosome 2, Soluble Starch Synthase 2 mapped on the same position as QTLs for starch phosphorylation, starch gelling temperature and amylose content. a-glucan, water dikinase co-localizes on chromosome 5 together with QTLs for starch phosphorylation and cold induced sweetening. Furthermore, the genes coding for two phosphorylases (StPho1a and StPho2) coincide with QTLs for starch gelling temperature, chipping colour and starch granule size on chromosome 2 and a QTL for starch phosphorylation on chromosome 9, respectively. The results suggest allelic variation acting on the genetics of the different traits

In tomato, carotenoids are important with regard to major breeding traits such as fruit colour and human health. The enzyme phytoene synthase (PSY1) directs metabolic flux towards carotenoid synthesis. Through TILLING (Targeting Induced Local Lesions IN Genomes), we have identified two point mutations in the Psy1 gene. The first mutation is a knockout allele (W180*) and the second mutation leads to an amino acid substitution (P192L). Plants carrying the Psy1 knockout allele show fruit with a yellow flesh colour similar to the r, r mutant, with no further change in colour during ripening. In the line with P192L substitution, fruit remain yellow until 3 days post-breaker and eventually turn red. Metabolite profiling verified the absence of carotenoids in the W180* line and thereby confirms that PSY1 is the only enzyme introducing substrate into the carotenoid pathway in ripening fruit. More subtle effects on carotenoid accumulation were observed in the P192L line with a delay in lycopene and b-carotene accumulation clearly linked to a very slow synthesis of phytoene. The observation of lutein degradation with ripening in both lines showed that lutein and its precursors are still synthesised in ripening fruit. Gene expression analysis of key genes involved in

Potato (Solanum tuberosum L.) is the world’s most important non-grain food crop and is central to global food security. It is clonally propagated, highly heterozygous, autotetraploid, and suffers acute inbreeding depression. Here we use a homozygous doubled-monoploid potato clone to sequence and assemble 86% of the 844-megabase genome. We predict 39,031 protein-coding genes and present evidence for at least two genome duplication events indicative of a palaeopolyploid origin. As the first genome sequence of an asterid, the potato genome reveals 2,642 genes specific to this large angiosperm clade. We also sequenced a heterozygous diploid clone and show that gene presence/absence variants and other potentially deleterious mutations occur frequently and are a likely cause of inbreeding depression. Gene family expansion, tissue-specific expression and recruitment of genes to new pathways contributed to the evolution of tuber development. The potato genome sequence provides a platform for genetic improvement of this vital crop

Background: Utilization of the natural genetic variation in traditional breeding programs remains a major challenge in crop plants. The identification of candidate genes underlying, or associated with, phenotypic trait QTLs is desired for effective marker assisted breeding. With the advent of high throughput -omics technologies, screening of entire populations for association of gene expression with targeted traits is becoming feasible but remains costly. Here we present the identification of novel candidate genes for different potato tuber quality traits by employing a pooling approach reducing the number of hybridizations needed. Extreme genotypes for a quantitative trait are collected and the RNA from contrasting bulks is then profiled with the aim of finding differentially expressed genes. Results: We have successfully implemented the pooling strategy for potato quality traits and identified candidate genes associated with potato tuber flesh color and tuber cooking type. Elevated expression level of a dominant allele of the ß-carotene hydroxylase (bch) gene was associated with yellow flesh color through mapping of the gene under a major QTL for flesh color on chromosome 3. For a second trait, a candidate gene with homology to a tyrosine-lysine rich protein (TLRP) was identified based on allele specificity of the probe on the microarray. TLRP was mapped on chromosome 9 in close proximity to a QTL for potato cooking type strengthening its significance as a candidate gene. Furthermore, we have performed a profiling experiment targeting a polygenic trait, by pooling individual genotypes based both on phenotypic and marker data, allowing the identification of candidate genes associated with the two different linkage groups. Conclusions: A pooling approach for RNA-profiling with the aim of identifying novel candidate genes associated with tuber quality traits was successfully implemented. The identified candidate genes for tuber flesh color (bch) and cooking type (tlr

A cytogenetic map has been developed for diploid potato (Solanum tuberosum), in which the arms of the 12 potato bivalents can be identified in pachytene complements using multicolor fluorescence in situ hybridization (FISH) with a set of 60 genetically anchored bacterial artificial chromosome (BAC) clones from the RHPOTKEY BAC library. This diagnostic set of selected BACs (five per chromosome) hybridizes to euchromatic regions and corresponds to well-defined loci in the ultradense genetic map, and with these probes a new detailed and reliable pachytene karyotype could be established. Chromosome size has been estimated both from microscopic length measurements and from 4',6-diamidino-2-phenylindole fluorescence-based DNA content measurements. In both approaches, chromosome 1 is the largest (100–115 Mb) and chromosome 11 the smallest (49–53 Mb). Detailed measurements of mega-base-pair to micrometer ratios have been obtained for chromosome 5, with average values of 1.07 Mb/µm for euchromatin and 3.67 Mb/µm for heterochromatin. In addition, our FISH results helped to solve two discrepancies in the potato genetic map related to chromosomes 8 and 12. Finally, we discuss the significance of the potato cytogenetic map for extended FISH studies in potato and related Solanaceae, which will be especially beneficial for the potato genome-sequencing project

Potato is a member of the Solanaceae, a plant family that includes several other economically important species, such as tomato, eggplant, petunia, tobacco and pepper. The Potato Genome Sequencing Consortium (PGSC) aims to elucidate the complete genome sequence of potato, the third most important food crop in the world. The PGSC is a collaboration between 13 research groups from China, India, Poland, Russia, the Netherlands, Ireland, Argentina, Brazil, Chile, Peru, USA, New Zealand and the UK. The potato genome consists of 12 chromosomes and has a (haploid) length of approximately 840 million base pairs, making it a medium-sized plant genome. The sequencing project builds on a diploid potato genomic bacterial artificial chromosome (BAC) clone library of 78000 clones, which has been fingerprinted and aligned into ~7000 physical map contigs. In addition, the BAC-ends have been sequenced and are publicly available. Approximately 30000 BACs are anchored to the Ultra High Density genetic map of potato, composed of 10000 unique AFLPTM markers. From this integrated genetic-physical map, between 50 to 150 seed BACs have currently been identified for every chromosome. Fluorescent in situ hybridization experiments on selected BAC clones confirm these anchor points. The seed clones provide the starting point for a BAC-by-BAC sequencing strategy. This strategy is being complemented by whole genome shotgun sequencing approaches using both 454 GS FLX and Illumina GA2 instruments. Assembly and annotation of the sequence data will be performed using publicly available and tailor-made tools. The availability of the annotated data will help to characterize germplasm collections based on allelic variance and to assist potato breeders to more fully exploit the genetic potential of potato

Background - The establishment of mutant populations together with the strategies for targeted mutation detection has been applied successfully to a large number of organisms including many species in the plant kingdom. Considerable efforts have been invested into research on tomato as a model for berry-fruit plants. With the progress of the tomato sequencing project, reverse genetics becomes an obvious and achievable goal. Results - Here we describe the treatment of Solanum lycopersicum seeds with 1% EMS and the development of a new mutated tomato population. To increase targeted mutant detection throughput an automated seed DNA extraction has been combined with novel mutation detection platforms for TILLING in plants. We have adapted two techniques used in human genetic diagnostics: Conformation Sensitive Capillary Electrophoresis (CSCE) and High Resolution DNA Melting Analysis (HRM) to mutation screening in DNA pools. Classical TILLING involves critical and time consuming steps such as endonuclease digestion reactions and gel electrophoresis runs. Using CSCE or HRM, the only step required is a simple PCR before either capillary electrophoresis or DNA melting curve analysis. Here we describe the development of a mutant tomato population, the setting up of two polymorphism detection platforms for plants and the results of the first screens as mutation density in the populations and estimation of the false-positives rate when using HRM to screen DNA pools. Conclusion - These results demonstrate that CSCE and HRM are fast, affordable and sensitive techniques for mutation detection in DNA pools and therefore allow the rapid identification of new allelic variants in a mutant population. Results from the first screens indicate that the mutagen treatment has been effective with an average mutation detection rate per diploid genome of 1.36 mutation/kb/1000 lines

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The increasing amount of available expressed gene sequence data makes whole-transcriptome analysis of certain crop species possible. Potato currently has the second largest number of publicly available expressed sequence tag (EST) sequences among the Solanaceae. Most of these ESTs, plus other proprietary sequences, were combined and used to generate a unigene assembly. The set of 246,182 sequences produced 46,345 unigenes, which were used to design a 44K 60-mer oligo array (Potato Oligo Chip Initiative: POCI). In this study, we attempt to identify genes controlling and driving the process of tuber initiation and growth by implementing large-scale transcriptional changes using the newly developed POCI array. Major gene expression profiles could be identified exhibiting differential expression at key developmental stages. These profiles were associated with functional roles in cell division and growth. A subset of genes involved in the regulation of the cell cycle, based on their Gene Ontology classification, exhibit a clear transient upregulation at tuber onset indicating increased cell division during these stages. The POCI array allows the study of potato gene expression on a much broader level than previously possible and will greatly enhance analysis of transcriptional control mechanisms in a wide range of potato research areas. POCI sequence and annotation data are publicly available through the POCI database

Background: After 10-year-use of AFLP (Amplified Fragment Length Polymorphism) technology for DNA fingerprinting and mRNA profiling, large repertories of genome- and transcriptome-derived sequences are available in public databases for model, crop and tree species. AFLP marker systems have been and are being extensively exploited for genome scanning and gene mapping, as well as cDNA-AFLP for transcriptome profiling and differentially expressed gene cloning. The evaluation, annotation and classification of genomic markers and expressed transcripts would be of great utility for both functional genomics and systems biology research in plants. This may be achieved by means of the Gene Ontology (GO), consisting in three structured vocabularies (i.e. ontologies) describing genes, transcripts and proteins of any organism in terms of their associated cellular component, biological process and molecular function in a species-independent manner. In this paper, the functional annotation of about 8,000 AFLP-derived ESTs retrieved in the NCBI databases was carried out by using GO terminology. Results: Descriptive statistics on the type, size and nature of gene sequences obtained by means of AFLP technology were calculated. The gene products associated with mRNA transcripts were then classified according to the three main GO vocabularies. A comparison of the functional content of cDNA-AFLP records was also performed by splitting the sequence dataset into monocots and dicots and by comparing them to all annotated ESTs of Arabidopsis and rice, respectively. On the whole, the statistical parameters adopted for the in silico AFLP-derived transcriptome-anchored sequence analysis proved to be critical for obtaining reliable GO results. Such an exhaustive annotation may offer a suitable platform for functional genomics, particularly useful in non-model species. Conclusion: Reliable GO annotations of AFLP-derived sequences can be gathered through the optimization of the experimental step

Enzymatic discoloration (ED) of potato tubers was investigated in an attempt to unravel the underlying genetic factors. Both enzyme and substrate concentration have been reported to influence the degree of discoloration and as such this trait can be regarded as polygenic. The diploid mapping population C x E, consisting of 249 individuals, was assayed for the degree of ED and levels of chlorogenic acid and tyrosine. Using this data, Quantitative Trait Locus (QTL) analysis was performed. Three QTLs for ED have been found on parental chromosomes C3, C8, E1, and E8. For chlorogenic acid a QTL has been identified on C2 and for tyrosine levels, a QTL has been detected on C8. None of the QTLs overlap, indicating the absence of genetic correlations between these components underlying ED, in contrast to earlier reports in literature. An obvious candidate gene for the QTL for ED on Chromosome 8 is polyphenol oxidase (PPO), which was previously mapped on chromosome 8. With gene-specific primers for PPO gene POT32 a CAPS marker was developed. Three different alleles (POT32-1, -2, and -3) could be discriminated. The segregating POT32 alleles were used to map the POT32 CAPS marker and QTL analysis was redone, showing that POT32 coincides with the QTL peak. A clear correlation between allele combinations and degree of discoloration was observed. In addition, analysis of POT32 gene expression in a subset of genotypes indicated a correlation between the level of gene expression and allele composition. On average, genotypes having two copies of allele 1 had both the highest degree of discoloration as well as the highest level of POT32 gene expression.