Plant sulfate transporters dealing with drought and salinity stress

For sustainable agriculture, significant improvement in abiotic stress (like drought and salinity) tolerance is necessary for any crop species. Sulfur acts as a key factor to combat abiotic stress in plants. Inorganic sulfate is absorbed from the environment through roots and then reduced and assimilated into cysteine, which is further utilized in production of other organic sulfur compounds in plants. Several compounds that are synthesized from sulfur metabolism have a free radical scavenging attribute that can reverse the adverse effects of abiotic stress. The sulfur uptake is governed by specific transporter proteins known as sulfate transporters (SULTRs), which are coded by a specific family of sulfate transporter genes. These SULTRs mediate both absorption and accumulation of sulfate within cells and translocation of sulfate at concerned parts of plant tissue. Also, they help in flowing out of sulfate from the vacuoles. The SULTRs have various kinds of functions depending on which species they belong to and thus can be divided into four groups. Group 1 shows high association for sulfate transport, whereas Group 2 shows low association for it. Group 3 mainly encodes for plastid and symbiosome membrane-associated transporters, and Group 4 encodes for vacuolar transporters. Drought and salt stress can also trigger Group 3 transporters, which results in their increased activity. Sulfate transporters in various plant species were studied for the past several years having different affinities and cell specificities. The SULTRs enable sulfate uptake by plants, thus helping to deal with abiotic stresses. In this chapter, different functions of sulfate transporters are discussed that hold great potential for enhancing sulfate transport capacities of crop plants under varying climatic conditions. An attempt has been made to enlist and understand different functions of different types of plant SULTRs associated with abiotic stress.