This project concerns a family of metal transporters called YELLOW STRIPE-LIKE (YSL), which have been identified based on their very strong sequence similarity to the YS1 protein of maize. The function of YS1 is in the primary uptake of iron from the soil. However, unlike other known plant iron transporters, YS1 transports iron that is complexed by specific plant-derived Fe(III) chelators called phytosiderophores. There are eight YSL proteins encoded in the Arabidopsis thaliana genome (www.bio.umass.edu/biology/ewalker), but they cannot function in phytosiderophore uptake, since Arabidopsis (like all non-grasses) can neither synthesize nor use phytosiderophores. Arabidopsis does make and use a related compound, nicotianamine, which is the biosynthetic precursor to phytosiderophores. Preliminary evidence suggests that YSL proteins mediate transport of metals bound to nicotianamine. The many roles of nicotianamine in achieving proper metal ion allocation in plants are incompletely understood, but there is strong evidence that nicotianamine is necessary for distribution of Fe, Zn, and Mn via phloem, and that it is required for transport of Cu in xylem.
The functions of the eight Arabidopsis thaliana YSL genes will be determined from the narrowest definition of function-biochemical function, to the broadest definition of function-the role of these proteins in the growth and development of the plant. A comprehensive description of the function of each YSL protein will be formed that will answer these questions: Which metals are transported by YSL proteins? Which cells express each YSL and therefore are involved in transporting these metals? Which nutrient conditions affect expression of each YSL family member? In what way(s) does abolishing specific YSL genes affect the pattern of metal ion distribution in the plant? By integrating this specific information for all eight YSL genes, our understanding of the metal ion allocation mechanisms used by plants will be greatly improved.
Sequence information will be made immediately available through Genbank and on the project website. The website will also be updated with experimental data for each YSL gene as it becomes available.
