Regulation of sulfate transport and assimilation in plants.

Plants as autotrophic organisms have a set of transporters and enzymes that mediate uptake and assimilation of inorganic sulfate and subsequent metabolic conversion to organic sulfur compounds. Studies in higher plants indicate the individual components of sulfate transport systems and enzymes for sulfate assimilation are consisted of multiple isoforms. Among these isoforms, several essential components are shown to have specific biochemical properties and localize in specific cellular and subcellular compartments. This chapter will describe the functions and regulation of sulfate transport systems and assimilatory enzymes, particularly focusing on the sulfate transporter gene family of a model plant species Arabidopsis thaliana. Recent findings provided evidence that the regulatory pathways are highly organized to balance the uptake, storage, and assimilation of sulfate in plants. In addition to the physiological and biochemical functions diversified among the isoforms of sulfate transporters, regulatory elements in transcriptional and posttranscriptional mechanisms were suggested to play significant roles in coordinating the assimilatory functions to adapt with varying sulfur nutritional status that fluctuates in the environment.