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ulence factors. But when Weiberg and his colleagues looked more

closely, they discovered that influencing expression wasn’t all the

transposons were doing: some of them were actually coding for

those plant-manipulating RNAs directly, and these RNAs play a

pivotal role in pathogenicity, according to results the researchers

published last August.^5 Not only do more-pathogenic strains have

more TE-derived RNAs, but when Weiberg’s team added TEs to

less-pathogenic individuals, those molds became more virulent,

causing larger lesions on the leaves of plants they infected.

While more research is needed, Weiberg says TEs could

explain the fungus’s promiscuity. The constant duplication and

subsequent mutation of TEs could give the mold “such a diverse

pool of small RNAs that no matter what plant species it is infect-

ing, there must be at least a few small RNAs that fit to the tran-

scriptome, or the mRNA, of this host species.”

TE mutations: Harder, better, faster, stronger

In addition to a growing body of evidence that transposons can

generate diversity in host genomes to drive change over millions of

years, Mirouze says TEs are likely major drivers of rapid evolution—

changes measured in terms of generations rather than millennia.

While González Pérez’s group has yet to conclusively dem-

onstrate that a TE is responsible for rapid evolutionary change

in wild flies, some of their analyses have suggested that recent,

VARIABLE ELEMENTS

“You can find transposable elements in virtually all the organisms that have been studied [genetically], from bacteria to

eukaryotes,” notes genomicist Josefa González Pérez of Pompeu Fabra University in Barcelona. But while TEs are nearly uni-

versal throughout living organisms, their prevalence varies widely. In some organisms, TEs dominate, accounting for up to

90 percent of the genome, while in others, transposable elements make up only a fraction of the entire genetic code. When

abundant, TEs can grow the size of the genome to enormous, unwieldy proportions that continue to baffle scientists.

100

80

60

40

20

0 54+39+3+90+63+20+15+85+19+3+2

Humans (Homo sapiens)

Total genome = 3.2Gb

Thale cress

(Arabidopsis thaliana)

Total genome = 0.15 Gb

Staphylococcus aureus

Total genome = 0.002 Gb

Japanese pufferfish

(Takifugu rubripes)

Total genome = 0.4 Gb

Mouse (Mus musculus)

Total genome = 2.5 Gb

Desert locust

(Schistocerca gregaria)

Total genome = 8.6 Gb

Caenorhabditis elegans

Total genome = 0.1 Gb

Lungfish (Neoceratodus forsteri)

Total genome= 43 Gb

Maize (Zea mays)

Total genome = 2.4 Gb

Baker’s yeast

(Saccharomyces cerevisiae)

Total genome = 0.12 Gb

Drosophila melanogaster

Total genome = 0.2 Gb

54%

39%

2.7%

63%

15%

20%

90%

85%

18.5%

Percentage of genome made up by transposable elements 3.4% 1-5%

DATA FROM: PLOS GENET, 17:E1009768, 2021; PLANT PHYSIOL, 139:1612–24, 2005; GENOME BIOL EVOL, 5:1886–901, 2013; GENOME BIOL, 10:107, 2009; NATURE, 590:284–89,

2021; SCIENCE, 297:1301–10, 2002; CYTOGENET GENOME RES, 147:217–39, 2015; BIORXIV, DOI:10.1101/2021.07.12.451456, 2021; NATURE, 420:520–62, 2002; F1000RES, 9:775,

2020; MOBILE DNA, 11:23, 2020; PLOS ONE, 6:E16526, 2011; C. ELEGANS II. 2ND EDITION, CSHL PRESS, 1997; BMC BIOINFORMAT, 20:484, 2019; PLOS ONE, 7:E50978, 2012;

CURR MICROBIOL, 62:198–208, 2011; J BACTERIOL, 194:4124, 2012

© JULIA MOORE,

WWW.MOOREILLUSTRATIONS.COM