The 'Christmas tree (Norwegian spruce) Picea abies
Seven times more DNA than a human.
Seven times more DNA than a human.
Try to get a creationist to explain the science behind that claim and you're likely to get nothing but rehearsed parrot squawks made in response to trigger words, if they don't run away hurling abuse and passive aggressive threats over their shoulder, or quickly change the subject. There will be no understanding of either information theory or thermodynamics.
The natural world is full of examples of how gene or even whole genome duplication creates redundant DNA and copies of genes than can mutate and be selected by natural selection to create new meaning in the genetic information. The Christmas tree, or Norwegian spruce, Picea abies, has about 29,000 functional genes (marginally more than a human) yet it has a genome seven times larger than the human genome, all packed into 12 chromosomes. The reason for this, according to a research team from Umeå universitet, Sweden, is because the mechanism for correcting duplication errors broke millions of years ago, so these duplications have been accumulating in the Picea abies genome ever since.
Creationists seem incapable of understanding the difference between information and the meaning in that information or how meaning is given by the environment. For example, a mutation which gave Streptococcus aureus resistance to the antibiotic, methicillin, would have had no meaning before medical science invented methicillin; now the same information makes MRSA an intractable condition and a highly successful pathogen. The point being that new meaning can arise without any change in the genome simply by a change in the environment, so evolution is not always dependent on change in genetic information.
Gene (including whole genome) duplication is common in nature, and especially in plants, where, unlike with most vertebrates save some lizards and amphibians, the normal state is diploid but many plants are polyploid. The delicious Coxes Orange Pippin apple is tetraploid, and the cultivated strawberry is octoploid, for example.
This false argument is often deployed by creationists as 'evidence' that evolution can't create new structure, which they assume requires an increase in genetic information, so is restricted to 'micro-evolution' based on another false assumption from their cult dogma - that evolution always involves increased complexity and an increase in information in the genome. The same people will also argue that humans are the most complex of organisms (because they have a lager brain, more intelligence, cultures, love, aesthetic appreciation, etc., etc., and, if there is anything to evolution, it means the process by which humans evolved by climbing the 'ladder' of increasing complexity, and now sit at the top as the pinnacle of directed evolution.
This would mean that humans should have the largest genome if it were remotely true. But in fact, the human genome size is fairly ordinary as genomes go and a mere dwarf compared to some.
Species
Common name
Ploidy level
Genome size (Gbp/1C)
Approx. length of DNA in a cell
Ostreococcus tauri
a unicellular marine green alga
Haploid
0.012
8 mm
Ananas comosus
Pineapple
Diploid
0.5
35 cm
Fragaria x ananassa
Strawberry
Octoploid
0.6
40 cm
Coffea arabica
Coffee
Tetraploid
1.2
80 cm
Cocos nucifera
Coconut
Diploid
2.7
1.8 m
Dionaea muscipula
Venus fly trap
Diploid
2.8
1.9 m
Homo sapiens
(male)
(male)
Man
Diploid
6.27
205 cm
Homo sapiens (female)
Woman
Diploid
6.37
205.23 cm
Allium cepa
Onion
Diploid
15.6
10.4 m
Aloe vera
Aloe
Diploid
16
10.7 m
Triticum aestivum
Bread wheat
Hexaploid
16.9
11.3 m
Pinus sylvestris
Pine tree
Diploid
22.5
15.0 m
Galanthus nivalis
Snowdrop
Diploid
35.3
23.5 m
Viscum album
Mistletoe
Diploid
95.1
63.3 m
Paris japonica
Japanese canopy plant
Octoploid
148.8
100 m
The reason these plants have such enormous genomes is because of repeated gene duplication and a massive amount of non-coding (redundant) DNA. The Japanese canopy plane, Paris japonica gets there by a combination of gene duplication and whole genome duplication in the form of eight copies of each chromosome.
According to creationists this massive duplication of information, each of which is replicated in every cell of the species, must be the result of magic creating new information, because, for dogmatic reasons, the observable instances of accidental duplication was impossible due to the second law of thermodynamics and information theory.
The point creationists have to pretend not to understand here is that if something can be observed to be happening, it is not impossible, therefore the notion (I won't grace it with the terms theory or hypothesis) which says it is impossible is wrong. It's little giveaway clues like this that would tell any rational person that creationism is a counter-factual superstition in which demonstrably false opinions are held to be unquestionable truths. The trick is to dismiss the evidence one way or another or ignore it altogether.
To ram home this point, here is the summary and introduction to a 1921 paper on the results of an investigation into the reason for mistletoe having such a massive genome consisting of just 10 chromosome pairs, (compared to the human 23 pairs plus 2 sex chromosomes):
SUMMARYIt should be perfectly clear then that creationists who claim no new genetic information can arise naturally are either fools who have believe the lies of creationist frauds, or are creationists frauds hoping to fool new recruit for the cult. New genetic information can and does arise naturally in a species' genome and new meaning can be imparted onto the information by changing the environmental context.
European mistletoe (Viscum album) is a hemiparasitic flowering plant that is known for its very special life cycle and extraordinary biochemical properties. Particularly, V. album has an unusual mode of cellular respiration that takes place in the absence of mitochondrial complex I. However, insights into the molecular biology of V. album so far are very limited. Since the genome of V. album is extremely large (estimated 600 times larger than the genome of the model plant Arabidopsis thaliana) it has not been sequenced up to now. We here report sequencing of the V. album gene space (defined as the space including and surrounding genic regions, encompassing coding as well as 5′ and 3′ non-coding regions). mRNA fractions were isolated from different V. album organs harvested in summer or winter and were analyzed via single-molecule real-time sequencing. We determined sequences of 39 092 distinct open reading frames encoding 32 064 V. album proteins (designated V. album protein space). Our data give new insights into the metabolism and molecular biology of V. album, including the biosynthesis of lectins and viscotoxins. The benefits of the V. album gene space information are demonstrated by re-evaluating mass spectrometry-based data of the V. album mitochondrial proteome, which previously had been evaluated using the A. thaliana genome sequence. Our re-examination allowed the additional identification of nearly 200 mitochondrial proteins, including four proteins related to complex I, which all have a secondary function not related to respiratory electron transport. The V. album gene space sequences are available at the NCBI.
INTRODUCTION
European mistletoe (Viscum album) is an obligate hemiparasitic flowering plant that grows on branches of various trees. It is supplied with water, minerals and organic compounds from the host. At the same time, V. album carries out photosynthesis and produces energy-rich compounds. Viscum album is widely distributed in central and northern Europe. It nicely is visible from November to March because it belongs to the few angiosperms that do not discard their leaves in the European winter. In fact, V. album is photosynthetically active at temperatures below the freezing point. Viscum album can cause problems in tree vitality, especially in combination with water stress. However, under favorable growth conditions, host trees are only moderately affected and can well coexist with the hemiparasite. European mistletoe has important ecological functions. Its flowers and berries ripe in winter and are a nutritional source for several insects and birds.
Compared to other flowering plants, the life cycle of V. album is characterized by numerous remarkable features (reviewed, e.g., in Glatzel and Geils, 2009): (i) V. album does not germinate in soil but on branches of trees, which requires particularly ‘sticky’ fruits (berries) that stably attach to tree bark; (ii) seeds consist of an embryo but lack a seed coat; (iii) embryos can germinate directly from the berry (without a dormancy phase); (iv) the direction of initial shoot growth is not determined by positive but rather negative phototropism, which guides the shoot onto the surface of the branch of the host tree; (v) the shoot afterwards penetrates the branch and gets connected to the xylem of the vascular system, where it forms a haustorium for uptake of water, minerals and organic compounds; (vi) the dichotomous mistletoe plant, which afterwards develops, forms one pair of shoot segments per year per shoot apical meristem and two comparatively simply organized leaves, which resemble primary leaves; (vii) shoots grow into all directions, giving rise to the typical ball-like shape of the adult plant (overall, the growth rate of V. album is low); (viii) in contrast to the leaves of the host tree, mistletoe leaves do not close stomata during water shortage (which may dramatically increase water stress of host plants); (ix) older leaves of the previous growth periods are discarded in September without preceding chlorophyll recycling; (x) leaves of the current growth period are kept during winter and perform photosynthesis; and (xi) fruit ripening and seed dispersal take place in winter.
Viscum album also has a particular biochemical composition. It is known for its rich content in phenolic acids, phenylpropanoids, flavonoids, triterpenes and phytosterols (Jäger et al., 2021; Urech and Baumgartner, 2015). It contains low-molecular-mass proteins designated viscotoxins as well as characteristic lectins (viscolectins), both of which contribute to its biotic defense system. The glue-like substances present in mistletoe berries mainly consist of hemicellulose compounds (Azuma et al., 2000). It is clear but hardly addressed by scientific investigations that the development of mistletoe is based on a very unusual distribution of phytohormones. Extracts of V. album have cytotoxic and immune-stimulating effects and are used in medicine (Nazaruk and Orlikowski, 2016).
On a molecular scale, V. album has been less characterized to date. Its mitochondrial and chloroplast genomes have been sequenced (Petersen et al., 2015.1a,b; Skippington et al., 2015.2, 2017) and were surprisingly found to lack some genes previously considered to be essential for multicellular eukaryotes, like genes encoding subunits of complex I of the mitochondrial respiratory chain. In contrast, the sequence of the nuclear genome has not been analyzed. The V. album genome consists of 2n = 20 chromosomes, is exceptionally large and is estimated to have a mass of 160 pg (80 pg for the haploid genome; average taken from the ‘Plant DNA C-values Database’, Pellicer and Leitch, 2019 [https://cvalues.science.kew.org/search]; original data from Nagl et al., 1983 [53.5 pg], Ulrich et al., 1988 [79.3 pg], Marie and Brown, 1993 [76 and 77.5 pg] and Zonneveld, 2010 [102.9 pg]). Indeed, the V. album genome is one of the largest genomes of any flowering plant known to date (Novák et al., 2020; Zonneveld, 2010). Its size has been estimated to be in the range of 88 × 109 base pairs (approximately 90 Gbp; Novák et al., 2020), which is 600 times the size of the genome of the model plant Arabidopsis thaliana (approximately 0.15 Gbp). Correspondingly, chromosomes of V. album are very large. Structural rearrangements in the chromosomes occur frequently and may cause large chromosome assemblies during meiosis (Barlow, 1981). The GC content is in the range of 39%, which is about average for flowering plants (Novák et al., 2020). An initial transcriptome analysis of V. album haustorium tissue has been performed and yielded sequences of 3044 open reading frames (Ko et al., 2014).
The gene content of seed plants (angiosperms and gymnosperms) is considered to be similar and amounts to approximately 0.03 Gbp (Novák et al., 2020). This implies that the gene content of V. album only covers 0.03% of its genome (20% in A. thaliana) and that the size of the inter-gene space is enormous. In general, genome size of eukaryotes correlates with the amount of repetitive DNA (Elliott and Gregory, 2015.3). Interestingly, this does not hold true for especially large genomes of seed plants (>10 Gbp), which unexpectedly were found not to have a further increased amount of repetitive DNA. In V. album, the genome proportion of repeats (copy number > 20) is 55% (Novák et al., 2020). This leaves much space for non-repetitive and low-copy DNA (excluding protein-coding genes).
Due to genome size and the amount of repetitive DNA, determination of the V. album genome sequence remains challenging. We therefore decided to firstly characterize the V. album gene space. The mRNA fraction was extracted from various organs of V. album, reverse-transcribed into cDNAs and subsequently used for systematic sequence determination by single-molecule real-time (SMRT) sequencing. We developed a database including >39 000 V. album gene sequences, which contain complete open reading frames encoding V. album proteins. Several new insights into the molecular biology of V. album are provided by an initial analysis of the deduced protein sequences and by re-evaluation of previously published V. album proteome data. The database is publicly available.
Schröder, L., Hohnjec, N., Senkler, M., Senkler, J., Küster, H. and Braun, H.-P. (2022),
The gene space of European mistletoe (Viscum album). Plant J, 109: 278-294. https://doi.org/10.1111/tpj.15558
Copyright: © 2021 The authors.
Published by John Wiley & Sons, Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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