Plant Molecular Biology 37: 989–999, 1998.
© 1998 Kluwer Academic Publishers. Printed in Belgium.
The behaviour of the autonomous maize transposable element En/Spm in
Arabidopsis thaliana allows efﬁcient mutagenesis
, Guillermo H. Cardon, Paul Fransz and Heinz Saedler
Max-Planck-Institut für Züchtungsforschung, Carl von Linn´e Weg 10, 50829 Köln, Germany (
Received 29 October 1997; accepted in revised form 26 February 1998
Key words: Arabidopsis thaliana, transposable element, En-1, mutagenesis, evolution
The behavior of the autonomous maize transposable element En/Spm of maize was studied in Arabidopsis.Trans-
genic Arabidopsis plants carrying En-1 elements were propagated for 12 generations using a single seed descent
procedure. The distribution and activity of the En-1 element was monitored using Southern DNA hybridisations
in generations 1, 6 and 12. In the ﬁrst generation the highest number of En-1 insertions per line was 7, which
increased to 20 in generation 12. The average number of En-1 insertions increased only slightly in the popula-
tion, due to a gradual accumulation of segregants that lost the transposable element. During the development of
the En-1 mutagenised population the element remained active even in the high-copy lines. In situ hybridisation
demonstrated that multiple En-1 insertions were distributed over all Arabidopsis chromosomes. From the initial
En-1 mutagenised populations many unstable gene mutations were recovered, indicating that En-1 can be used as
a efﬁcient tool for gene tagging in Arabidopsis.
Transposable elements and retrotransposons are
widely distributed among higher plants . Retro-
transposons moveby replicative transposition and thus
can accumulate to large copy numbers in the genome
. In contrast, transposable elements transpose via
excision and reintegration and thus their copy num-
ber is usually stable in a population. The structure
and mode of transposition of classical transposable
elements is well known in various plants, most promi-
nently in Zea mays . The presence of transposable
elements in plants is indicated by the fact that they
frequently induce variegated mutations . Ac and
En/Spm in Zea mays [13, 21, 22, 26, 27] and Tam
elements in Anthirrhinum majus  induce mutations
in two ways: by integrating into a gene causing a mu-
tation, or by imprecise excision generating mutations
at the site of excision .
Consequences of transposable element insertions
thus include a reduction or loss of gene expression
leading to recessive mutations or, rarely, to ectopic
gene expression yielding a gain of function [6, 18,
20]. In addition, transposable elements may cause
chromosomal rearrangements [3, 20].
In order to develop an efﬁcient and simple transpo-
son mutagenesis system, the autonomous maize En-1
element was introduced into the genome of Arabidop-
sis thaliana ecotype Columbia and its activity was
studied throughout 12 successive generations. En-1
belongs to the CACTA family of transposable ele-
ments . Mechanisticfeatures ofEn-1 in Arabidopsis
were found to be very similar to its behaviour in its
natural host, Z. mays , suggesting that En-1 may
also be an efﬁcient mutator element in Arabidopsis.
Here we describe the development and properties of
a transposon tagging system employing multiple-copy
En-1 insertions in A. thaliana.