phylogenomics_intro_vertebrata

Phylogenomics tutorial based on BUSCO genes

Disclaimer To follow the demo and make the most of it, it helps if you have some basic skills with running software tools and manipulating files using the Unix shell command line. It assumes you have Docker installed on your computer (tested with Docker version 18.09.7, build 2d0083d; on Ubuntu 18.04).

Introduction

We will be reconstructing the phylogenetic relationships of some (iconic) vertebrates based on previously published whole genome data. The list of species we will be including in the analyses, and the URL for the data download can be found in this table.

All software used in the demo is deposited as Docker images on Dockerhub and all data is freely and publicly available.

The workflow we will demonstrate is as follows:

• Download genomes from Genbank
• Identifying complete BUSCO genes in each of the genomes
• pre-filtering of orthology/BUSCO groups
• For each BUSCO group:
  • build alignment
  • trim alignment
  • identify model of protein evolution
  • infer phylogenetic tree (ML)
• construct supermatrix from individual gene alignments
• infer phylogenomic tree with paritions corresponding to the original gene alignments using ML
• map internode certainty (IC) onto the phylogenomic tree

Let's begin

Before you get going I suggest you download this repository, so have all scripts that you'll need. Ideally you'd do it through git.

(user@host)-$ git clone https://github.com/chrishah/phylogenomics_intro_vertebrata.git

Then move into the newly cloned directory, and get ready.

(user@host)-$ cd phylogenomics_intro_vertebrata

1.) Download data from Genbank

What's the first species of vertebrate that pops into your head? Latimeria chalumnae perhaps? Let's see if someone has already attempted to sequence its genome. NCBI Genbank is usually a good place to start. Surf to the webpage and have a look. And indeed we are lucky.

Let's get it downloaded. Note that the (user@host)-$ part of the code below just mimics a command line prompt. This will look differently on each computer. The command you actually need to exectue is the part after that, so only, e.g. mkdir assemblies:

#First make a directory and enter it
(user@host)-$ mkdir assemblies
(user@host)-$ mkdir assemblies/Latimeria_chalumnae
(user@host)-$ cd assemblies/Latimeria_chalumnae


#use the wget program to download the genome
(user@host)-$ wget https://ftp.ncbi.nlm.nih.gov/genomes/all/GCF/000/225/785/GCF_000225785.1_LatCha1/GCF_000225785.1_LatCha1_genomic.fna.gz

#decompress for future use
(user@host)-$ gunzip GCF_000225785.1_LatCha1_genomic.fna.gz

#leave the directory for now
(user@host)-$ cd ../..

We have compiled a list of published genomes that we will be including in our analyses here - the actual text file ships with the repository here: data/samples.csv. You don't have to download them all now, but do another few just as practice. You can do one by one or use your scripting skills (for loop) to get them all in one go.

To keep things clean I'd suggest to download each into a separate directory that should be named according to the binomial (connected with underscores, rather than spaces, see the first column of the file data/samples.csv), following the same logic as in the example for L. chalumnae above.

TASK

Try to download two more genomes, specifically the ones listed in the file data/samples.exercise.csv. Organize each of the two in its own directory as for L. chalumnae above:

• create a directory with the species name as in column 1 of the file data/samples.exercise.csv in the assemblies directory
• change directory into this newly created directory
• download the genome using the url in the file (column 2)
• change directory back to your original starting place

Ideally you could write a for loop to do it. A script that would achive this (for inspiration) can be found in data/download_loop.sh.

Once you're done you can check what you have by finding all files that end in *gz in the assemblies directory:

(user@host)-$ find ./assemblies/ -name "*gz"

2.) Run BUSCO on each assembly

In order to identify a defined set of genes in all of our genomes we could use BUSCO, i.e. run it on each of the downloaded genomes.

Attention

Since these genomes are relatively large BUSCO takes quite a while to run so this step has been already done for you.

A reduced representation of the BUSCO results (reference BUSCO set 'vertebrata_odb10') for each species ships with the repository in the directory results/orthology/busco/busco_runs.

Take a few minutes to explore the reports.

Challenge

Find out how complete the coelacanth (Latimeria chalumnae) genome is according to the BUSCO assessment.

3.) Prefiltering of BUSCO groups

Now, assuming that we ran BUSCO across a number of genomes, we're going to select us a bunch of BUSCO genes to be included in our phylogenomic analyses. Let's get and overview.

We have a script to produce a matrix of presence/absence of BUSCO genes across multiple species. Let's try it out. In this tutorial we'll be using Docker containers through Singularity.

(user@host)-$ singularity exec docker://reslp/biopython_plus:1.77 \
              bin/extract_busco_table.py \
              --hmm results/orthology/busco/busco_set/vertebrata_odb10/hmms \
              --busco_results results/orthology/busco/busco_runs/ \
              -o busco_table.tsv

The resulting file busco_table.tsv can be found in your current directory.

ATTENTION

When calling singularity as above it will download the corresponding container from the cloud. This is very convenient, but might in some instances take a bit of time. If you are doing this exercise as part of a course you might be provided with local copies of the images to save some time. Please wait here to get instructions.

The following command would download the image and safe it to a local *.sif file.

(user@host)-$ singularity pull docker://reslp/biopython_plus:1.77
(user@host)-$ ls -hrlt

Note that the previous command singularity pull .. downloaded a file called biopython_plus_1.77.sif - this is a physical representation of the image. Note also the naming scheme. Singularity names the file by combining the image name with the version (the part after the ':') via a '_', so 'biopython_plus:1.77' becomes 'biopython_plus_1.77.sif'.

To use the *.sif file instead of always querying the cloud the command before could be adjusted to:

(user@host)-$ singularity exec biopython_plus_1.77.sif \
              bin/extract_busco_table.py \
              --hmm results/orthology/busco/busco_set/vertebrata_odb10/hmms \
              --busco_results results/orthology/busco/busco_runs/ \
              -o busco_table.tsv

ATTENTION

If you're doing this as part of a course, all images may have been downloaded for you already.

Please check for example: ls ~/Share/Singularity_images/ or ask the instructors. Then, in all subsequent singularity calls please use the local images, rather than querying the cloud, so instead of:

singularity exec docker://reslp/biopython_plus:1.77 ..

adjust to

singularity exec ~/Share/Singularity_images/biopython_plus_1.77.sif ..

Full list of local images that could be used to replace cloud images (in case they are provided to you):

docker://reslp/biopython_plus:1.77	->	~/Share/Singularity_images/biopython_plus_1.77.sif
docker://reslp/clustalo:1.2.4	->	~/Share/Singularity_images/clustalo_1.2.4.sif
docker://reslp/trimal:1.4.1	->	~/Share/Singularity_images/trimal_1.4.1.sif
docker://reslp/iqtree:2.0.7	->	~/Share/Singularity_images/iqtree_2.0.7.sif
docker://reslp/astral:5.7.1	->	~/Share/Singularity_images/astral_5.7.1.sif

Moving on..

Next, we'd want for example to identify all genes that are present in at least 20 of our 25 taxa and concatenate the sequences from each species into a single fasta file. We made a script for that - see below. Please make sure to follow the instructions also with respect to creating new directories, when this is suggested!.

(user@host)-$ mkdir -p by_gene/raw
(user@host)-$ singularity exec docker://reslp/biopython_plus:1.77 \
              bin/create_sequence_files.py \
              --busco_table busco_table.tsv \
              --busco_results results/orthology/busco/busco_runs \
              --cutoff 0.5 \
              --outdir by_gene/raw \
              --minsp 20 \
              --type aa \
              --gene_statistics gene_stats.txt \
              --genome_statistics genome_statistics.txt 

A bunch of files have been created in your current directory (gene_stats.txt) and also in the directory by_gene/raw (per gene fasta files).

4.) For each BUSCO group

For each of the BUSCOs that passed we want to:

• do multiple sequence alignment
• filter the alignment, i.e. remove ambiguous/problematic positions
• build a phylogenetic tree

Let's go over a possible solution step by step for gene: 409625at7742.

Perform multiple sequence alignment with clustalo.

#alignment with clustalo
(user@host)-$ mkdir by_gene/aligned
(user@host)-$ singularity exec docker://reslp/clustalo:1.2.4 \
              clustalo \
              -i by_gene/raw/409625at7742_all.fas \
              -o by_gene/aligned/409625at7742.clustalo.fasta \
              --threads=2

We can then look at the alignment result (by_gene/aligned/409625at7742.clustalo.fasta). There is a number of programs available to do that, e.g. MEGA, Jalview, Aliview, or you can do it online. A link to the upload client for the NCBI Multiple Sequence Alignment Viewer is here (I suggest to open in new tab). Download the alignment (by_gene/aligned/409625at7742.clustalo.fasta) to your local computer, upload the file to the online tool, press 'Close' button, and have a look.

What do you think? It's actually quite messy..

Let's move on to score and filter the alignment, using TrimAl.

#alignment trimming with trimal
(user@host)-$ mkdir by_gene/trimmed
(user@host)-$ singularity exec docker://reslp/trimal:1.4.1 \
              trimal \
              -in by_gene/aligned/409625at7742.clustalo.fasta \
              -out by_gene/trimmed/409625at7742.clustalo.trimal.fasta \
              -gappyout

Try open the upload dialog for the Alignment viewer in a new tab and upload the new file (by_gene/trimmed/409625at7742.clustalo.trimal.fasta). What do you think? The algorithm has removed quite a bit at the ends of the original alignment, reducing it to only ~100 positions, but these look mostly ok, at first glance.

Now, let's infer a ML tree with IQtree.

#ML inference with IQTree
(user@host)-$ mkdir -p by_gene/phylogeny/409625at7742
(user@host)-$ singularity exec docker://reslp/iqtree:2.0.7 \
              iqtree \
              -s by_gene/trimmed/409625at7742.clustalo.trimal.fasta \
              --prefix by_gene/phylogeny/409625at7742/409625at7742 \
              -m MFP --seqtype AA -T 2 -bb 1000

The best scoring Maximum Likelihood tree can be found in the file: by_gene/phylogeny/409625at7742/409625at7742.treefile.

The tree is in the Newick tree format. There is a bunch of programs that allow you to view and manipulate trees in this format. You can only do it online, for example through iTOL, embl's online tree viewer. There is others, e.g. ETE3, icytree, or trex. You can try it out, but first let's have a quick look at the terminal.

(user@host)-$ cat by_gene/phylogeny/409625at7742/409625at7742.treefile

Go to the iTOL, select 'Upload a tree' and copy/paste the textual representation of our tree into the 'Tree text' field.

What do you think? Does it look right? Remember that this is based on one gene, and different genes may tell different stories depending on their history, which may be affected by many factors.

Well done!

5.) Run the process for multiple genes

Now, let's say we want to go over these steps for multiple genes, say these:

• 359032at7742
• 413149at7742
• 409719at7742
• 406935at7742

TASK

Create a script called per_gene_inference.sh for the purpose.

For loop would do the job, right? See the below code as a template.

• adjust to use local singularity images instead of querying Dockerhub
• add in the tree inference step - make sure to organise the result as in the example above, i.e. make a directory by_gene/phylogeny/<gene_id> and run IQTree so that its results are placed there.
• run the script

#!/bin/bash
for gene in $(echo "359032at7742 413149at7742 409719at7742 406935at7742")
do
        echo -e "\n$(date)\t$gene"

        echo -e "$(date)\taligning"
        singularity exec docker://reslp/clustalo:1.2.4 clustalo -i by_gene/raw/${gene}_all.fas -o by_gene/aligned/${gene}.clustalo.fasta --threads=2

        echo -e "$(date)\ttrimming"
        singularity exec docker://reslp/trimal:1.4.1 trimal -in by_gene/aligned/${gene}.clustalo.fasta -out by_gene/trimmed/${gene}.clustalo.trimal.fasta -gappyout

        echo -e "$(date)\ttree inference"
	#your code here

        echo -e "$(date)\tDone"
done

A possible solution for the script (including the tree inference) can be found here: backup/bygene_local.sh. This one makes use of local images, assuming they are provided to you. Another version here (backup/bygene.sh) would be more general and fetch the images from the cloud if not yet present.

Run your script, e.g. like so:

#########  in case you don't want to make your own script you can copy the one provided to you e.g.:
(user@host)-$ cp backup/bygene_local.sh bygene.sh

(user@host)-$ chmod a+x bygene.sh # make sure it's executable
(user@host)-$ ./bygene.sh # execute the script

If something went wrong and you want to continue anyway you can get the data you'd have produced in the previous step by copying it from our backup directory.

(user@host)-$ rsync -avpuzP backup/by_gene/* by_gene

Well Done! Now you should have five trees - one for each of the genes. Just to doublecheck:

(user@host)-$ ls -1 by_gene/phylogeny/*/*treefile
by_gene/phylogeny/359032at7742/359032at7742.treefile
by_gene/phylogeny/406935at7742/406935at7742.treefile
by_gene/phylogeny/409625at7742/409625at7742.treefile
by_gene/phylogeny/409719at7742/409719at7742.treefile
by_gene/phylogeny/413149at7742/413149at7742.treefile

Now, then, let's infer a ML tree using a supermatrix of all 5 genes that we have processed so far. Conveniently, you'll just need to point IQtree onto a directory that contains multiple alignments and it will do the rest. In our case we use the trimmed alignments. Be aware, though, that in order for IQtree to be able to match up the right sequences in the supermatrix you're going to have to use the same names in all individual alignment files.

(user@host)-$ singularity exec docker://reslp/iqtree:2.0.7 \
              iqtree \
              -s by_gene/trimmed/ \
              --prefix five_genes \
              -m MFP --seqtype AA -T 2 -bb 1000 

This will run for about 10 Minutes. You can check out the result five_genes.treefile, once it's done.

(user@host)-$ cat five_genes.treefile #or try backup/five_genes.treefile instead if you had trouble

Now, we can also try to build a speciestree from the 5 individual gene trees using ASTRAL.

TASK

First bring the individual gene trees together into one file. Let's call the file trees.txt.

Then run ASTRAL.

(user@host)-$ singularity exec docker://reslp/astral:5.7.1 \
               java -jar /ASTRAL-5.7.1/Astral/astral.5.7.1.jar \
               -i trees.txt -o species_tree.astral.tre 

Have a look at the result.

(user@host)-$ cat species_tree.astral.tre #or try backup/species_tree.astral.tre instead if you had trouble

Instead of looking at the plain text representation you can also explore the trees e.g. via iTOL.

Congratulations, you've just built your first phylogenomic tree(s)!!!

5.) Automate the workflow with Snakemake

A very neat way of handling this kind of thing is Snakemake.

The very minimum you'll need to create Snakemake workflow is a so called Snakefile. The repository ships with files called Snakemake_intro/Snakefile_local and Snakemake_intro/Snakefile_cloud. This file contains the instructions for running a basic workflow with Snakemake. Let's have a look.

(user@host)-$ less Snakemake_intro/Snakefile_local #exit less with 'q' - the version to use local images
(user@host)-$ less Snakemake_intro/Snakefile_cloud #exit less with 'q' - the version to use images from the cloud

In the Snakefile you'll see 'rules' (that's what individual steps in the analyses are called in the Snakemake world). Some of which should look familiar, because we just ran them manually, and then again within a simple for loop. Filenames etc. are replaced with variables but other than that..

Spend some time to explore the file.

Snakemake should be installed on your system - check back with your instructors if you're doing this as part of a course. An easy way to get it set up is through conda. A conda envirnoment has most likely been set up for you, if you're doing this as part of a course. If you haven't set it up yet, we provide some instructions here.

Assuming you've set up a conda environment called snakemake (this will usually be the case if you do this as part of a course), in order to run Snakemake you first need to enter this environment.

(user@host)-$ conda activate snakemake
(snakemake) (user@host)-$ snakemake -h

Now, let's try to do a Snakemake 'dry-run', providing a specific target file and see what happens. You'll first need to put a file called Snakefile in place - this is the default expectation of Snakemake.

(user@host)-$ cp Snakemake_intro/Snakefile_local Snakefile #or cp Snakemake_intro/Snakefile_cloud Snakefile if you prefer to query the cloud
(user@host)-$ snakemake -n -rp \
                 auto/trimmed/193525at7742.clustalo.trimal.fasta

Now, you could extend the analyses to further genes.

(user@host)-$ snakemake -n -rp \
                 auto/trimmed/193525at7742.clustalo.trimal.fasta \
                 auto/trimmed/406935at7742.clustalo.trimal.fasta

Actually, running would happen if you remove the -n flag. Note that I've added another flag (--use-singularity) which tells snakemake to use containers for certain rules if so indicated in the Snakefile.

(user@host)-$ snakemake -rp --cores 2 --use-singularity \
                 auto/trimmed/193525at7742.clustalo.trimal.fasta \
                 auto/trimmed/406935at7742.clustalo.trimal.fasta

Now try the following:

• Check what happens if you run the above command once again.
• remove the file auto/trimmed/406935at7742.clustalo.trimal.fasta and rerun the command. Neat, no?

See if you can get it run also for gene id 378120at7742.

TASK

Try to extend the Snakefile to also include:

• per gene phylogenetic inference (see above)
• supermatrix tree inference using the following 5 genes

Perform the analyses for the following genes:

• 409625at7742
• 409719at7742
• 413149at7742
• 42971at7742
• 97645at7742

Have fun playing around with this for a while ;-)

Solutions can be found in these files:

• backup/Snakefile_with_ml_local
• backup/Snakefile_with_ml

The tree based on a supermatrix built from alignments of the above 5 genes also ships with the repository - see backup/super.5.treefiles.

TASK

Finally, let's try adjust the Snakefile to automatically consider all alignments that are present in the directory by_gene/raw.

A Snakefile that would do the full analyses using all genes that are present in the directory by_gene/raw/ can be found here:

• backup/Snakefile_with_ml_from_dir_local
• backup/Snakefile_with_ml_from_dir

Try it out:

(user@host)-$ snakemake -n --cores 2 -rp --use-singularity \
                 -s backup/Snakefile_with_ml_from_dir_local

If you were to run the above (not dry-run, i.e. remove the -n flag) it will take ~30 Minutes. The best tree will be written to a file called super.from_dir.treefile. If you didn't manage to run it but are still interested in the tree it ships with the repo here: backup/super.from_dir.treefile

Check it out in iTOL.

Create yourself a dag (directed acyclic graph) to see what the current status of the workflow is.

(user@host)-$ snakemake -n --dag -s backup/Snakefile_with_ml_from_dir_local | dot -Tpdf > dag.with_ml_from_dir.pdf

The result will look something like this.

6.) Full automation (OPTIONAL)

The current repository is actually a snapshot of phylociraptor. This is a pipeline for automating the entire process of phylogenomic analyses from BUSCO genes (for now).

In the base directory of this repository you could resume an analysis as shown below. If there is time we'll talk about the setup a little bit.

The main things you need are:

• config file data/config.vertebrata_minimal.yaml
• sample file data/vertebrata_minimal.csv

A few steps were already run for you - see the file data/preparation.md

#get table
./phylociraptor orthology -t serial=2 --config-file data/config.vertebrata_minimal.yaml

#filter-orthology
./phylociraptor filter-orthology -t serial=2 --config-file data/config.vertebrata_minimal.yaml --verbose

#align
./phylociraptor align -t serial=2 --config-file data/config.vertebrata_minimal.yaml --verbose

#filter align
./phylociraptor filter-align -t serial=2 --config-file data/config.vertebrata_minimal.yaml --verbose

#modeltest
./phylociraptor modeltest -t serial=2 --config-file data/config.vertebrata_minimal.yaml

#ml tree
./phylociraptor mltree -t serial=2 --config-file data/config.vertebrata_minimal.yaml --verbose

#speciestree
./phylociraptor speciestree -t serial=2 --config-file data/config.vertebrata_minimal.yaml --verbose

#figure
./phylociraptor report --config-file data/config.vertebrata_minimal.yaml 
./phylociraptor report --figure --config-file data/config.vertebrata_minimal.yaml