Preface

Transposable elements (TEs) are ubiquitous mobile DNA sequences found in both prokaryotic and eukaryotic genomes. They are able to insert at different positions of the genome, either by excising from one position and reinserting into another or by replicating into daughter copies. TEs are particularly abundant in plant genomes, where they can represent over 80 % of the bulk of large cereal genomes. Their discovery by B.McClintock, and the subsequent introduction of the notion of genome fluidity, was a major shift in our concepts on heredity. TEs can dramatically modify the structure of host genomes, affect genome sizes and generate genetic variation, not only by transposition but also by providing the raw material for genomic rearrangements due to their repetitive nature. Until recently, and in spite of B. Mc Clintock’s seminal concept of “Controlling Elements,” the impact of TEs on host genome function was merely regarded as circumstantial. A rather different representation has been brought to light in the last decade, which strongly argues that TEs may also act as pivotal factors in generating genic variation and modulating cellular gene expression. This book is intended at presenting the latest advances on the importance of TEs and on their impact on plant genome dynamics and function. The TE research scene has recently seen major advances, with new tools such as Next Generation Sequencing (NGS) technologies opening tremendous possibilities for rapid global analyses of genomes at reduced costs. This has led to an exponential increase in the amount of TE-related data and to a deeper knowledge of their impact on host genomes. As a consequence, all plant researchers engaged in genomic studies are more or less unwillingly bumping into this wealth of TEs and are now realizing that these TEs cannot be discarded as annoying junk sequences anymore. TEs are encountered in both genomic and transcriptomic data, and in a tremendous variety of elements, including highly defective and deleted versions sometimes mobilized at surprisingly high levels via related copies, making their classification a difficult task. There is therefore a need for researchers to find guidelines to recognize and classify TEs and better understand their importance and potential impact.