Plant ABC Transporters

Preface

ABC (ATP-binding cassette) proteins are ubiquitous, membrane-intrinsic trans-porters that catalyze the primary (ATP-dependent) movement of their substrates over biological membranes. Until know, the special challenge of ABC transporter work lies in the identification of ABC transporter substrates. Therefore, in higher plants, ABC transporters were—in functional analogy to their mammalian orthologs—initially identified as central part of a detoxification process in that they sequester conjugated xenobiotics from the cytoplasm into the central vacuole. However, mainly genetic work in the last decade has provided the discovery of unexpectedly diverse ABC transporter substrates that include beside chlorophyll catabolites and xenobiotic conjugates, heavy metals, lipids, terpenoids, lignols, and organic acids. According to their associated wide biological function, plant ABCs were found beside on vacuolar membranes also on the plasma membrane and on membranes of other organelles, including the plastids, peroxisomes, itochondria and the endoplasmic reticulum. The discovery that members of the ABCB and ABCG family are involved in the cellular and intercellular movement of phytohor-mones, such as auxins (IAA and IBA), abscisic acid (ABA), cytokinin, and most probably also strigolactones, has boosted their investigation and provided a new
perception of the whole family. Further, recent work on ABC transporters has left the Arabidopsis limits and been extended to dicot and monocot crop plants, which has caused considerable interest also outside the plant community.
This book is therefore devoted to the exciting plethora of plant ABC transporter substrates and highlights their tightly connected biological functions that accordingly reach from cellular detoxification, over development, to symbiosis and defense. It contains a special focus on “phytohormone transporters” and several chapters converging on the trafficking, regulation, and structure–function of ABCB-type auxin transporters. Moreover, it especially emphasizes the role of ABC transporters in plant defense and the symbiosis between plant and microorganisms, such as arbuscular mycorrhiza and rhizobia root nodules. Finally, it encompasses also a set of chapters that center on ABC protein structure and ABC evolution.

I would like to express my deepest gratitude to the ABC transporter community for pushing this exciting field so tremendously forward in the last decade. But also for contributing to this little milestone, making it what it was initially meant to be: a complete, timely, and beautiful overview on Plant ABC Transporters for the expert.
And a teaser for the beginner: there is much more to explore!
Fribourg, Switzerland Markus Geisler
March 17, 2014

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