Identification, phylogenetic analysis and expression profiling of ABC transporter family of Crocus sativus L: A step towards understanding apocarotenoid transport

Terpenoid Transport in Plants: How Far from the Final Picture?

Contrary to the biosynthetic pathways of many terpenoids, which are well characterized and elucidated, their transport inside subcellular compartments and the secretion of reaction intermediates and final products at the short- (cell-to-cell), medium- (tissue-to-tissue), and long-distance (organ-to-organ) levels are still poorly understood, with some limited exceptions. In this review, we aim to describe the state of the art of the transport of several terpene classes that have important physiological and ecological roles or that represent high-value bioactive molecules. Among the tens of thousands of terpenoids identified in the plant kingdom, only less than 20 have been characterized from the point of view of their transport and localization. Most terpenoids are secreted in the apoplast or stored in the vacuoles by the action of ATP-binding cassette (ABC) transporters. However, little information is available regarding the movement of terpenoid biosynthetic intermediates from plastids and the endoplasmic reticulum to the cytosol. Through a description of the transport mechanisms of cytosol- or plastid-synthesized terpenes, we attempt to provide some hypotheses, suggestions, and general schemes about the trafficking of different substrates, intermediates, and final products, which might help develop novel strategies and approaches to allow for the future identification of terpenoid transporters that are still uncharacterized.

Pathways for Carotenoid Biosynthesis, Degradation, and Storage

Carotenoids are isoprenoid compounds synthesized de novo in all photosynthetic organisms as well as in some nonphotosynthetic bacteria and fungi. In plants, carotenoids are essential for light harvesting and photoprotection. They contribute to the vivid color found in many plant organs. The cleavage of carotenoids produces small molecules (apocarotenoids) that serve as aroma compounds, as well as phytohormones and signals to affect plant growth and development. Since carotenoids provide valuable nutrition and health benefits for humans, understanding of carotenoid biosynthesis, catabolism and storage is important for biofortification of crops with improved nutritional quality. This chapter primarily introduces our current knowledge about carotenoid biosynthesis and degradation pathways as well as carotenoid storage in plants.