OGU 1.998

Organelle Genome Utilities

Quick start

• Install Python 3 (3.9 or newer).

• Open terminal, run

  # Install, using pip (recommended)
  pip3 install OGU --user
  
  # Initialize with Internet
  # Windows
  python -m OGU init
  # Linux and macOS
  python3 -m OGU init
  
  # Run
  # Windows
  python -m OGU
  # Linux and macOS
  python3 -m OGU
  

Table of Contents

• Quick start
• Feature
• Prerequisite
  • Hardware
  • Software
• Installation
  • Portable
  • Install with pip
  • Install with conda
  • Initialization
• Usage
  • Quick examples
  • Sequence ID
  • Command line
• Input
• Output
• Options
  • gb2fasta
  • evaluate
  • primer
• Performance
• Citation
• License
• Q&A

Features

:heavy_check_mark: Automatically collect, organize and clean sequence data from NCBI GenBank or local: collect data with abundant options; extract CDS, intergenic spacer, or any other annotations from original sequence; remove redundant sequences according to species information; remove invalid or abnormal sequences/fragments; generate clean dataset with uniform sequence id.

:heavy_check_mark: Evaluate variance of sequences by calculating nucleotide diversity, observed resolution, Shannon index, tree resolution, phylogenetic diversity (original and edited version), gap ratio, and others. Support sliding-window scanning.

:heavy_check_mark: Design universal primer for the alignment. Support ambiguous bases in primers.

:heavy_check_mark: Visualize the evolution pattern of different gene or non-coding sequences in the organelle of one taxa instead of a single species.

Prerequisite

Hardware

Organelle Genome Utilities (OGU) requires very few computational resources. A normal PC/laptop is enough. For downloading large amount of data, make sure the Internet connection is stable and fast enough.

Software

For the portable version, nothing need to be installed manually.

For installing from pip, Python is required. Notice that the python version should be higher than 3.8.

:white_check_mark: All third-party dependencies will be automatically installed with Internet, including biopython, matplotlib, coloredlogs, numpy, primer3-py, (python packages), and MAFFT, IQTREE, BLAST.

Installation

We assume that users have already installed Python3 (3.9 or above).

Install with pip

1. Install Python. 3.9 or newer is required.

2. Open command line, run

pip3 install OGU --user

Initialization

During the first running, OGU will check and initialize the running environment. Missing dependencies will be automatically installed.

This step requires Internet connection.

By default, the program will automatically finish initialization, if any error occurs, users can choose one of the following methods:

Automatic

Run the following command.

# Windows
python -m OGU init
# Linux and macOS
python3 -m OGU init

Use prepared package

According to your system, download related compressed file from packages.

For Windows users:

1. paste %HOMEDRIVE%%HOMEPATH%/ to explorer's address bar and open.
2. create .OGU folder. Don't miss the dot.
3. open .OGU folder, paste downloaded compressed file and unzip. Make sure after decompress there are three folders in .OGU.

For Linux and macOS users, please download and unpack files into ~/.OGU.

Manually install

For Linux users with root privileges, just use the package manager:

# Ubuntu and Debian
sudo apt install mafft ncbi-blast+ iqtree
# Fedora (1)
sudo dnf install mafft ncbi-blast+ iqtree
# Fedora (2)
sudo yum install mafft ncbi-blast+ iqtree
# ArchLinux
sudo pacman -S mafft ncbi-blast+ iqtree
# FreeBSD
sudo pkg install mafft ncbi-blast+ iqtree

For macOS users with root privileges, install brew if it has not been installed previously:

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

If any errors occur, install Xcode-select and retry.

Then:

brew install blast mafft brewsci/science/iqtree

If using Windows or lacking root privileges, users should follow these instructions:

1. BLAST+

   • Windows
   • Linux and macOS

2. MAFFT

   • Windows

     Choose "All-in-one version", download and unzip. Then follow the steps in the BLAST+ installation manual to set the PATH.

   • Linux

     Choose "Portable package", download and unzip. Then follow the instructions of BLAST+ to set the PATH for MAFFT.

   • macOS

     Choose "All-in-one version", download and unzip. Then follow the steps in the BLAST+ installation manual to set the PATH.

3. IQ-TREE

   • Download

     Download the installer according to OS. Unzip and add the path of subfolder bin to PATH.

Usage

Graphical user interface

Open the command line (Windows) or terminal (Linux and macOS), run

OGU

or

# linux and macos
python3 -m OGU
# windows
python -m OGU

command line

Once a user opens the command line (Windows) or terminal (Linux and macOS), just type the command:

# Windows
python -m OGU [input] -[options] -out [out_folder]
# Linux and macOS
python3 -m OGU [input] -[options] -out [out_folder]

Quick examples

1. Download all rbcL sequences of species in Poaceae family and do pre-process.

# Windows
python -m OGU.gb2fasta -gene rbcL -taxon Poaceae -out rbcL_Poaceae
# Linux and macOS
python3 -m OGU.gb2fasta -gene rbcL -taxon Poaceae -out rbcL_Poaceae

2. Download all ITS sequences of Rosa genus. Do pre-process and keep redundant sequences:

# Windows
python -m OGU.gb2fasta -query internal transcribed spacer -taxon Rosa -out Rosa_its -uniq no
# Linux and macOS
python3 -m OGU.gb2fasta -query internal transcribed spacer -taxon Rosa -out Rosa_its -uniq no

3. Download all Lamiaceae chloroplast genomic sequences in the RefSeq database. Then do pre-process and evaluation of variance (skip primer designing):

# Windows
python -m OGU -og cp -refseq yes -taxon Lamiaceae -out Lamiaceae_cp
# Linux and macOS
python3 -m OGU -og cp -refseq yes -taxon Lamiaceae -out Lamiaceae_cp

4. Download sequences of Zea mays, set length between 100 bp and 3000 bp, and then perform evaluation and primer designing. Note that the space in the species name is replaced with underscore "_".

# Windows
python -m OGU -taxon Zea_mays -min_len 100 -max_len 3000 -out Zea_mays -primer
# Linux and macOS
python3 -m OGU -taxon Zea_mays -min_len 100 -max_len 3000 -out Zea_mays -primer

5. Download all Oryza mitochondria genomes in RefSeq database, keep the longest sequence for each species and run a full analysis:

# Windows
python -m OGU -taxon Oryza -og mt -min_len 50000 -max_len 200000 -uniq longest -out Oryza_cp -refseq yes -primer
# Linux and macOS
python3 -m OGU -taxon Oryza -og mt -min_len 50000 -max_len 200000 -uniq longest -out Oryza_cp -refseq yes -primer

Sequence ID

Organelle Genome Utilities uses a uniform sequence id format for input fasta files and all output sequences.

Locus|Kingdom|Phylum|Class|Order|Family|Genus|Species|Accession|SpecimenID_Isolate|Type
# example
rbcL|Viridiplantae|Streptophyta|Magnoliopsida|Poales|Poaceae|Oryza|longistaminata|MF998442|TAN:GB60B-2014|gene

The order of the fields is fixed. The fields are separated by vertical bars ("|"). The space character (" ") was disallowed and was replaced by an underscore ("_"). Due to missing data, some fields may be empty.

Locus: SeqName refers to the name of a sequence. Usually it is the gene name. For intergenic spacer, an underscore ("_") is used to connect two gene's names, e.g., "geneA_geneB".

If a valid sequence name cannot be found in the annotations of the GenBank file, Organelle Genome Utilities will use "Unknown" instead.

For chloroplast genes, if "-rename" option is set, the program will try to use regular expressions to fix potential errors in gene names.

Kingdom: The kingdom (Fungi, Viridiplantae, Metazoa) of a species. For convenience, a superkingdom (Bacteria, Archaea, Eukaryota, Viruses, Viroids) may be used if the kingdom information for a sequence is missing.

Phylum: The phylum of the species.

Class: The class of the species.

Because some species' classes are empty (for instance, basal angiosperm), Organelle Genome Utilities will guess the class of the species.

Given the taxonomy information in GenBank file:

Eukaryota; Viridiplantae; Streptophyta; Embryophyta; Tracheophyta;
    Spermatophyta; Magnoliophyta; basal Magnoliophyta; Amborellales;
    Amborellaceae; Amborella.

Organelle Genome Utilities will use "basal Magnoliophyta" as the class because this expression locates before the order name ("Amborellales").

Order: The order name of the species.

Family: The family name of the species.

Genus: The genus name of the species, i.e., the first part of the scientific name.

Species: The specific epithet of the species, i.e., the second part of the scientific name of the species. It may contain the subspecies' name.

Accession: The GenBank Accession number for the sequence. It does not contain the record's version.

SpecimenID and Isolate: Specimen ID and Isolate ID of the sequence. May be empty.

Type: Type of the sequence. It is usually "gene" or "spacer".

Command line

:exclamation: In Linux and macOS, Python2 is python2 and Python3 is python3. However, in Windows, Python3 is called python, too. Please notice the difference.

• Show help information of each module

# Windows
python -m OGU -h
python -m OGU.gb2fasta -h
python -m OGU.evaluate -h
python -m OGU.primer -h
# Linux and macOS
python3 -m OGU.gb2fasta -h
python3 -m OGU.evaluate -h
python3 -m OGU.primer -h

• Full process

# Windows
python -m OGU -gene [gene name] -taxon [taxon name] -og [organelle type] -out [output name]
# Linux and macOS
python3 -m OGU -gene [gene name] -taxon [taxon name] -og [organelle type] -out [output name]

• Collect, convert, and clean GenBank data with gb2fasta module

# Windows
python -m OGU.GB2fasta -gene [gene name] -taxon [taxon name] -og [organelle type] -out [output name]
# Linux and macOS
python3 -m OGU.gb2fasta -gene [gene name] -taxon [taxon name] -og [organelle type] -out [output name]

• Evaluate variance of given fasta files

# Windows
python -m OGU.evaluate -fasta [fasta files]
# Linux and macOS
python3 -m OGU.evaluate -fasta [input file]

• Design universal primers of given alignments.

# Windows
python -m OGU.primer -aln [alignment files]
# Linux and macOS
python3 -m OGU.primer -aln [alignment files]

Visualize

This function is designed to visualize the evolution pattern of organelle genomes within a taxon ( order, family, or genus) rather than focusing on a single species.

Note

1. It is recommended to select a reference genome with high-quality annotation. Bad annotation may lead to gene missing in the figure.
2. For plastid genomes, a portion of the rps12 gene may be omitted from the figure due to the large size of its "intron".
3. Plastid genome structure information is required for visualization. Users can obtain size data from papers or use tools such as OGDRAW, NOVOWrap, or Chloroplot to determine the size.
4. For mitochondrial genomes, the D-loop region may be omitted due to potential naming conflicts. Users are advised to review the Evaluation.csv file and reference genome file before running the visualization.
5. The output figure is in PDF format. Users can edit the figure to improve its appearance, particularly for overlapping label text. Inkscape, an open-source, cross-platform and free software is recommended.

Input

1. input_csv: The sequence variance evaluation result from the OGU.Evaluate module.
2. ref_gb: A reference genome file containing only one organelle genome. Generated from OGU.GB2fasta with the "-out_debug" option. Since plastid and animal mitochondrial genome structures are generally stable, users only need to select one as a representative.
3. taxon: If ref_gb is empty, OGU will automatically generate a reference genome file for visualization purposes. It is recommended to use this option instead of ref_gb, but users must ensure a stable internet connection.
4. og_type: Organelle type. Use cp for plastid and mt for mitochondria.
5. lsc, ssc, and ir: Plastid structure sizes. If the input is a mitochondria genome, leave these fields empty.
6. output: Output folder. The result will be a "Figure.pdf" file within the folder.

Command-Line Interface

To use the command-line interface, run OGU.visualize.

Graphical User Interface

1. Click Visualize on the main window of the GUI.
2. Click Load example and select the organelle type to load example data. Or to input your own data.
3. Click Run to execute the program.

Jupyter Notebooks

Jupyter notebooks are available for analyzing the visualization results in detail using circular figures:

• draw_circle_plastid.ipynb: For plastid genomes
• draw_circle_mitochondria.ipynb: For mitochondrial genomes

To use these notebooks:

1. Install JupyterLab by running pip3 install jupyterlab.
2. Double-click the notebook to open it in Jupyter Notebook, Visual Studio Code, or another preferred IDE.
3. Edit the filename variable to point to the Evaluation.csv file obtained from OGU.Evaluate.
4. Edit the gb_file variable to point to the extended gb file obtained from OGU.GB2fasta. Remember to generate it with the "-out_debug" option in OGU.gb2fasta.
5. If visualizing plastid data, provide the lengths of LSC, SSC, IRa, and IRb. Or use the default values, which are based on Tobacum.
6. Customize color themes as desired.
7. Run all cells to generate the PDF figure output.

Input

Organelle Genome Utilities accepts:

1. GenBank queries. Users can use "-query" or combine with any other filters;
2. GenBank-format files.
3. Unaligned fasta files. Each file is considered as one locus when evaluating the variance;
4. Alignments (fasta format).

Output

All results will be put in the output folder. If the user does not set the output path via "-out", Organelle Genome Utilities will create a folder labelled "Result".

In the output folder, several sub-folders will be created.

• GenBank

  Raw GenBank files.

• Divide

  Fasta files converted from the GenBank file. Each file represents a fragment of the original sequence according to the annotation.

  For instance, a record in a "rbcL.gb" file may also contain atpB gene's sequences. The "rbcL.fasta" file does not contain any upstream/downstream sequences and "atpB_rbcL.fasta" does not have even one base of the atpB or rbcL gene, just the spacer (assuming the annotation is precise).

  User can skip this dividing step with the option "-no_divide".

• Fasta

  Raw fasta files users provided.

• Unique

  Fasta files after removing redundant sequences.

• Expanded_fasta

  To design primers, Organelle Genome Utilities extend a sequence to its upstream/downstream. Only used in the primer module.

• Alignment

  Aligned fasta files.

  .aln: The aligned fasta files.

  .-consensus.fastq: The fastq format of the consensus sequence of the alignment. Note that it contains alignment gap ("-"). It is NOT RECOMMENDED to be used directly because the consensus-generating algorithm is optimised for primer design.

• Evaluate

  Including output files from the evaluation module.

  .pdf: The PDF format of the figure containing the sliding-window scan result of the alignment.

  .csv: The CSV format file of the sliding-window scan result. "Index" means the location of the base in the alignment.

• Primer

  Including output files from the primer module.

  .primer.fastq: The fastq format file of a primer's sequence. It contains two sequences, and the direction is 5' to 3'. The first is the forward primer, and the second is the reverse primer. The quality of each base is equal to its proportion of the column in the alignment. Note that the sequence may contain ambiguous bases if it was not disabled.

  .primers.csv: The list of primer pairs in CSV (comma-separated values text) format.

  .candidate.fasta: The candidate primers. This file may contain thousands of records. Do not recommend paying attention to it.

  .candidate.fastq: Again, the candidate primers. This time, each file has the quality information that equals to the proportion of the bases in the column of the alignment.

• Temp

  Including temporary files. Could be safely deleted .

In the output folder, there are some other important output files:

• Primers.csv

  The list of primer pairs in CSV (comma-separated values text) format.

  Its title:

  Locus,Samples,Score,AvgProductLength,StdEV,MinProductLength,MaxProductLength,Coverage,Observed_Res,Tree_Res,PD_terminal,Entropy,LeftSeq,LeftTm,LeftAvgBitscore,LeftAvgMismatch,RightSeq,RightTm,RightAvgBitscore,RightAvgMismatch,DeltaTm,AlnStart,AlnEnd,AvgSeqStart,AvgSeqEnd
  

  Locus: The name of the locus/fragment.

  Samples: The number of sequences used to find this pair of primers.

  Score: The score of this pair of primers. Usually the higher, the better.

  AvgProductLength: The average length of the DNA fragment amplified by this pair of primers.

  StdEV: The standard deviation of the AvgProductLength. A higher number means the primer may amplify different lengths of DNA fragments.

  MinProductLength: The minimum length of an amplified fragment.

  MaxProductLength: The maximum length of an amplified fragment. Note that all of these fields are calculated using given sequences.

  Coverage: The coverage of this pair of primers over the sequences it used. Calculated with the BLAST result. High coverage means that the pair is much more "universal".

  Observed_Res: The observed resolution of the sub-alignment sliced by the primer pair, which is equal to the number of unique sequences divided by the number of total sequences. The value is between 0 and 1.

  

  Tree_Res: The tree resolution of the sub-alignment, which is equal to the number of internal nodes on a phylogenetic tree (constructed from the alignment) divided by number of terminal nodes. The value is between 0 and 1.

  

  PD_terminal: The average of the terminal branch's length. It's an edited version of the Phylogenetic Diversity for DNA barcoding evaluation.

  Entropy: The Shannon equitability index of the sub-alignment. The value is between 0 and 1.

  

  LeftSeq: Sequence of the forward primer. The direction is 5' to 3'.

  LeftTm: The melting temperature of the forward primer. The unit is degree Celsius (°C).

  LeftAvgBitscore: The average raw bitscore of the forward primer, which is calculated by BLAST.

  LeftAvgMismatch: The average number of mismatched bases of the forward primer, as counted by BLAST.

  RightSeq: Sequence of reverse primer. The direction is 5' to 3'.

  RightTm: The melting temperature of the reverse primer. The unit is degrees Celsius (°C).

  RightAvgBitscore: The average raw bitscore of the reverse primer, which is calculated by BLAST.

  RightAvgMismatch: The average number of mismatched bases of the reverse primer, as counted by BLAST.

  DeltaTm: The difference in the melting temperatures of the forward and reverse primers. A pair of primers with a high DeltaTm may result in failure during the PCR experiment.

  AlnStart: The location of the beginning of the forward primer (5', leftmost of primer pairs) in the entire alignment.

  AlnEnd: The location of the end of the reverse primer (5', rightmost of primer pairs) in the entire alignment.

  AvgSeqStart: The average beginning of the forward primer in the original sequences. ONLY USED FOR DEBUG.

  AvgSeqEnd: The average end of the forward primer in the original sequences. ONLY USED FOR DEBUG.

  The primer pairs are sorted by Score. Since the score may not fully satisfy the user's specific considerations, it is suggested that primer pairs be chosen manually if the first primer pair fails during the PCR experiment.

• Log.txt

  The log file. Contains all the information printed on the screen.

• Evaluation.csv

  The summary of all loci/fragments, which only contains the variance information for each fragment. One of the new field, GapRatio, means the ratio of the gap ("-") in the alignment. PD means the original version of the phylogenetic diversity and PD_stem means an alternative version of it which only calculate the length of the stem branch in the phylogenetic tree.

Options

Here are some general options for the program and submodule:

-h: Prints help messages of the program or one of the module.

-gb [filename]: User-provided GenBank file or files. Could be one or more files that separated by space.

For instance,

# one file
-gb sequence.gb
# multiple files
-gb matK.gb rbcL.gb Oryza.gb Homo_sapiens.gb

-fasta [filename]: User-provided unaligned fasta files. Could be one or multiple.

-aln [filename]: Alignment files that the user provides. Could be one or multiple.

It only supports the fasta format. Ambiguous bases and gaps ("-") are supported.

-out [folder name]: The output folder's name. All results will be put into the output folder. If the user does not set an output path via "-out", Organelle Genome Utilities will create a folder named "Result".

OGU does not overwrite the existing folder with the same name.

It is HIGHLY RECOMMENDED to use only letters, numbers and underscores ("_") in the folder name to avoid mysterious errors caused by other Unicode characters.

Options below are for specific modules.

gb2fasta

Query

Options used for querying NCBI GenBank.

-taxon [taxonomy name]: The taxonomy name. It could be any taxonomic rank from kingdom (same as "-group") to species, as long as the user inputs correct name (the scientific name of species or taxonomic group in latin, NOT ENGLISH). It will restrict the query to the targeted taxonomy unit. Make sure to use quotation marks if taxonomy has more than one word or use underscore to replace space, for instance "Zea mays" or Zea_mays.

-gene [gene name]: The gene's name which the user wants to query in GenBank. If the user wants to use logical expressions like "OR", "AND", "NOT", s/he should use "-query" instead. If there is space in the gene's name, make sure to use quotation marks.

Note that "ITS" is not a gene name--it is "internal transcribed spacer".

Sometimes "-gene" options may bring in unwanted sequences. For example, if a user queries "rbcL[gene]" in GenBank, spacer sequences may contain rbcL or rbcL's upstream/downstream gene, such as "atpB_rbcL spacer" or atpB.

-og [ignore|both|no|mt|mitochondrion|cp|chloroplast|pl|plastid]: Query organelle sequences or not. The default value is ignore.

- `ignore`: do not consider organelle type, same as GenBank website's
  default setting.

- `both`: only query organelle sequences, including both plastid and
  mitochondrion.

- `no`: exclude organelle sequences from the query.

- `cp` or `chloroplast` or `pl` or `plastid`: only query plastid sequences

- `mt` or `mitochondrion`: only query mitochondrion sequences.

-refseq [both|yes|no]: query in RefSeq database or not. The default value is both.

- `both`: query all sequences in or not in RefSeq database, same as NCBI
  website's default setting.

- `yes`: only query sequences in RefSeq database.

- `no`: exclude sequences in RefSeq database.

RefSeq is considered to have higher sequence and annotation quality than GenBank. This option could be used for getting nuclear/organelle genomes from NCBI. In this situation (-refseq yes), the length limit will be removed automatically.

-count [number]: Restrict numbers of sequences to be downloaded. The default value 0 means no restriction.

-min_len [length]: The minimum length of the records downloaded from GenBank. The default value is 100 (bp). The number must be an integer.

-max_len [length]: The maximum length of the records downloaded from GenBank. The default value is 10000 (bp). The number must be an integer.

-date_start [yyyy/mm/dd]: The beginning of the release data range of the sequences, the format is yyyy/mm/dd.

-date_end [yyyy/mm/dd]: The end of the release data range of the sequences, the format is yyyy/mm/dd.

-molecular [all|DNA|RNA]: The molecular type, which could be DNA or RNA. The default is all--no restriction.

-email [email address]: NCBI GenBank database requires users to provide an email address in case of abnormal situations that NCBI need to contact the user. For convenience, OGU will use "[e-mail]" if the user does not provide an email address. However, it is better to provide a real email address for potential contact.

-query [expression]: The query string provided by the user. It behaves in the same manner as the query the user typed into the Search Box in NCBI GenBank's webpage.

Make sure to follow NCBI's grammar for queries. It can contain several words. Remember to add quotation marks if an item contains more than one words, for instance, "Homo sapiens"[organism], or use underscore to replace space, Homo_sapiens[organism].

-exclude [expression]: Use this option to use negative option. For instance, "-exclude Zea [organism]" (do not include quotation marks) will add " NOT (Zea[organism])" to the query.

This option can be useful for excluding a specific taxon.

-taxon Zea -exclude "Zea mays"[organism]

This will query all records in genus Zea while records of Zea mays will be excluded.

For much more complex exclude options, please consider to use "Advance search" in GenBank website.

-group [all|animals|plants|fungi|protists|bacteria|archaea|viruses]: To restrict the query in given group. The default value is all--no restriction.

It is reported that the "group" filter may return abnormal records, for instance, return plants' records when the group is "animal" and the "organelle" is "chloroplast". Furthermore, it may match a great number of records in GenBank. Hence, we strongly recommend using "-taxon" instead.

Divide

Options used for converting GenBank files to fasta files.

-out_debug: If you are going to use visualize pipeline to draw detailed circle figure, use this option to generate extended version genbank file.

-no_divide: If set, it will analyse the whole sequence instead of the divided fragments. By default, OGU divides one GenBank record into several fragments according to its annotation.

-rename: If set, the program will try to rename genes. For instance, "rbcl" will be renamed to "rbcL", and "tRNA UAC" will be renamed to "trnVuac", which consists of "trn", the amino acid's letter and transcribed codon. This may be helpful if the annotation has nonstandard uppercase/lowercase or naming format that it can merge the same sequences to one file for the same locus having variant names.

If using Windows operating system, consider using this option to avoid contradictory filenames.

-unique [longest|first|no]: The method used to remove redundant sequences. OGU will remove redundant sequences to ensure only one sequence per species by default. A user can change its behaviour by setting different methods.

- `first`: According to the records' order in the original GenBank file,
  only the first sequence of the same species' same locus will be kept.
  Others will be ignored directly. This is the default option due to
  performance considerations.

- `longest`: Keep the longest sequence for one species. The program will
  compare the sequence's length from the same species' same locus.

- `no`: Skip this step. All sequences will be kept.

-allow_mosaic_spacer: If one gene nested with another gene, normally they do not have spacers. The default value is False.

However, some users want the fragments between two gene's beginnings and ends. This option is for this specific purpose (e.g., matK-trnK_UUU). For normal usage, do not recommend.

-expand [number]: The expansion length in upstream/downstream. If set, OGU will expand the sequence to its upstream/downstream after the dividing step to find primer candidates. The default value is 0.

Note that this option is different with "-max_len". This option limits the length of one annotation's sequence. The "-max_len" limits the whole sequence's length of one GenBank record.

-allow_repeat: If genes repeated in downstream, this option will allow the repeat region to be extracted, otherwise any repeated region will be omitted. The default value is False.

-allow_invert_repeat: If two genes invert-repeated in downstream, this option allow the second spacer's name to be different with the first one. Combine with -allow_repeat, two spacers will be kept. If only one is needed, just set -allow_invert_repeat and do not set -allow_repeat omitted. The default value is False.

For instance, geneA-geneB located in one invert-repeat region (IR) of chloroplast genome. In another IR region, there are geneB-geneA. This option will extract sequences of two different direction as two unique spacers.

-max_name_len [number]: The maximum length of a feature name. Some annotation's feature name in GenBank file is too long, and usually, they are not the target sequence the user wants. By setting this option, OGU will truncate the annotation's feature name if it is too long. By default, the value is 50.

-max_gene_len [value]: The maximum length of a sequence for one annotation. Some annotations' sequences are too long (for instance, one gene has two exons, and its intron is longer than 10 Kb). This option will skip those long sequences. By default, the value is 20000 (bp).

Evaluate

-ig or -ignore_gap: ignore gaps in the alignment. Missing data is typically represented as the letter “N”. Our software retains “N” in its original form for records containing it. During sequence variance analysis, “N” is treated as an equal mixture of the four nucleotides (“ATCG”) when calculating Pi, observed resolution, and the Shannon Index. Indels are represented as hyphens (“-”) in the alignment. For sequence variance analysis, hyphens are treated as a virtual fifth base when calculating Pi, observed resolution, and the Shannon Index, receiving the same treatment as the four DNA bases.

-iab or -ignore_ambigous: ignore ambiguous bases in the alignment. Ambiguous bases are treated as equal mixtures of the possible bases. For example, the letter “Y”, which represents either C or T, is treated as the sum of one-half “C” and one-half “T.”

-quick: skip sliding-window scan.

-size [number]: the window size of the sliding window scan. The default value is 500.

-step [number]: the step size of the sliding window scan. The default value is 50.

-skip_primer: skip primer designing. The default value is False.

Primer design

-coverage [value]: The minimum coverage of the base and primer. The default value is 0.5 (50%). It is used to remove primer candidates if its coverage among all sequences is smaller than the threshold. The coverage of primers is calculated by BLAST.

-res [value]: The minimum observed resolution of the fragments or primer pairs. The default value is 0.3 (30%). The value should be in 0.0 to 1.0.

OGU uses the observed resolution instead of others because of the speed. Also, it is considered to be the lower bound of the real resolution that a fragment with a low observed resolution may not have a satisfactory tree resolution/phylogenetic diversity, either.

-pmin [length]: The minimal length of the primer. The default value is 20.

-pmax [length]: The maximal length of the primer. The default value is 25.

-topn [number]: How many pairs of primers is kept for each input alignment. The default value is 1, i.e., only keep the best primer pair according to its score. To keep more pairs, set "-t" to more than 1.

-amin [length]: The minimum amplified length (include primer). The default value is 300 (bp). Note this limits the PCR product's length instead of the sub-alignment's length.

-amax [length]: The maximum amplified length (include primer). The default value is 800 (bp).

The "-amin" and "-amax" are used to screen primer candidates. It uses BLAST results to set the location of primers on each template sequence and calculates the average lengths of the products. Because of the variance of species, the same locus may have different lengths in different species, plus with the stretching of the alignment that gaps were added during the aligning, please consider adding some margins for these two options.

For instance, if a user wants the amplified length to be smaller than 800 and greater than 500, s/he could consider setting "-amin" to 550 and "-amax" to

-ambiguous [number]: The maximum number of ambiguous bases allowed in one primer. The default value is 4.

-mismatch [number]: The maximum number of mismatched bases in a primer. This option is used to remove primer candidates if the BLAST results show that there is too much mismatch. The default value is 4.

Performance

For a taxon that is not very large and includes few fragments, OGU can finish the task in minutes. For a large taxon (such as the Asteraceae family or the whole class of the Poales) containing multiple fragments (such as the chloroplast genomes), the time to complete may be one hour or more on a PC or laptop.

OGU requires few memories (usually less than 0.5 GB, although, for a large taxon BLAST may require more) and few CPUs (one core is enough). It can run very well on a normal PC. Multiple CPU cores may be helpful for the alignment and tree construction steps.

For Windows users, MAFFT may be very slow due to antivirus software. Please consider following this instruction to install Ubuntu on Windows to obtain better results.

Citation

As yet unpublished.

License

The software itself is licensed under AGPL-3.0 (not include third-party software).

Q&A

Please submit your questions in the Issue page :smiley:

• Q: The first-time run is slow.

  A: OGU will automatically install third-party software (MAFFT/BLAST/IQTREE) from AWS at first-time running. Microsoft Windows users, especially in some regions may have slow connection. Please be patient, or you can manually install them. See Initialization.

• Q: During the installation process, I am prompted that some Python packages cannot be installed.

  A: It is recommended that you try using a virtual environment to isolate OGU from the operating system.

  # create a virtual environment named "myvenv"
  python3 -m venv myvenv
  # activate the environment
  # linux and macos
  source myvenv/bin/activate
  # windows
  myvenv/Scripts/activate.ps1
  # install
  pip3 install OGU