Plant Systematics and Evolution (2018) 304:521–533
An insight into the evolution of introns in the gyrase A gene of plants
· Dhirendra Fartyal
· V. Mohan M. Achary
· Aakrati Agarwal
· Malireddy K. Reddy
Received: 28 January 2017 / Accepted: 28 January 2018 / Published online: 19 February 2018
© Springer-Verlag GmbH Austria, part of Springer Nature 2018
DNA gyrase is a type II topoisomerase essential for replication and transcription in prokaryotes and eukaryotic cell organelles.
The functional gyrase enzyme is an A
tetramer encoded by the gyrA and gyrB genes. Most of the eukaryotic gyrase A
genes possess introns while they are intron-less in prokaryotes. In the present study, we found out the evolutionary passage
of intron development in gyrase A gene with the help of bioinformatics approaches. All the plant gyrase A genes studied by
us were found to be a part of the nuclear genome, and their respective proteins were targeted to the organelles. Except the
green alga Bathycoccus prasinos, these genes contained introns, and the positions of the homologous introns were found to
be highly conserved in diverse plant lineages despite having variation in their nucleotide sequence compositions and lengths.
However, in red, brown, and green algae: Chlorella variabilis and Chlamydomonas reinhardtii, homologous intron posi-
tions were not conserved, which might be due to the independent acquisition of introns. The study makes it amply evident
that the introns appeared in the gene following endosymbiotic gene transfer of the gyrase A to the nuclear genome of an
ancestral green plant. The land plants appear to have acquired intron-bearing gyrase A gene from a common ancestral green
algae and subsequently lesser re-arrangement of introns at homologous positions resulted in their positional conservation.
However, the introns which are known to be under lesser selection pressure evolved diﬀerently in various plant species in
terms of base composition and lengths.
Keywords Endosymbiosis · Gyrase A · Introns · Introns early model · Introns late model
The replication and transcription processes in prokaryotes
are dependent on DNA gyrase enzyme, a type II topoisomer-
ase (type II indicates the ability of DNA gyrase to transiently
break both strands of DNA) (Wang 1996; Champoux 2001).
The enzyme, an A
tetramer encoded by the gyrA and
gyrB genes, catalyzes negative supercoils in DNA during
replication and transcription, which is a critical process
for survival of the cells (Cozzarelli 1980; Gellert 1981).
Eukaryotic nuclear genomes do not require gyrase activity
as the negative supercoiling in DNA is achieved by wrap-
ping up of DNA molecules around the histone proteins, and
the relaxation of DNA molecules is carried out by gyrase-
like type I and type II topoisomerases. On the other hand,
organellar genomes, i.e., of chloroplast and mitochondria
do not possess histones and essentially require the presence
of DNA gyrase enzyme to supercoil and relax their DNA.
Previous studies and sequencing data available in databases
conﬁrm that DNA gyrase genes are a part of nuclear genome
of eukaryotes and the proteins encoded by them are targeted
Handling Editor: Jim Leebens-Mack.
Mrinalini Manna, Dhirendra Fartyal, and V. Mohan M. Achary
have equally contributed to this work.
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s0060 6-018-1503-6) contains
supplementary material, which is available to authorized users.
* Mrinalini Manna
* Dhirendra Fartyal
Crop Improvement Group, International Centre for Genetic
Engineering and Biotechnology, Aruna Asaf Ali Marg,
New Delhi 110 067, India
Uttarakhand Technical University, Dehradun, India
Plant Molecular Biology Lab, Department of Botany,
University of Delhi, New Delhi, India