In the endopterygote Drosophila melanogaster, Zelda is an activator of the 
zygotic genome during the maternal-to-zygotic transition (MZT). Zelda binds 
cis-regulatory elements (TAGteam heptamers), making chromatin accessible for 
gene transcription. Zelda has been studied in other endopterygotes: 
Apis mellifera and Tribolium castaneum, and the paraneopteran Rhodnius prolixus. 
We studied Zelda in the cockroach Blattella germanica, a hemimetabolan, short 
germ-band, and polyneopteran species. B. germanica Zelda has the complete set of 
functional domains, which is typical of species displaying ancestral features 
concerning embryogenesis. Interestingly, we found D. melanogaster TAGteam 
heptamers in the B. germanica genome. The canonical one, CAGGTAG, is present at 
a similar proportion in the genome of these two species and in the genome of 
other insects, suggesting that the genome admits as many CAGGTAG motifs as its 
length allows. Zelda-depleted embryos of B. germanica show defects involving 
blastoderm formation and abdomen development, and genes contributing to these 
processes are down-regulated. We conclude that in B. germanica, Zelda strictly 
activates the zygotic genome, within the MZT, a role conserved in more derived 
endopterygote insects. In B. germanica, zelda is expressed during MZT, whereas 
in D. melanogaster and T. castaneum it is expressed beyond this transition. In 
these species and A. mellifera, Zelda has functions even in postembryonic 
development. The expansion of zelda expression beyond the MZT in endopterygotes 
might be related with the evolutionary innovation of holometabolan 
metamorphosis. DATABASES: The RNA-seq datasets of B. germanica, D. melanogaster, 
and T. castaneum are accessible at the GEO databases GSE99785, GSE18068, 
GSE63770, and GSE84253. In addition, the RNA-seq library from T. castaneum adult 
females is available at SRA: SRX021963. The B. germanica reference genome is 
available as BioProject PRJNA203136.