Current understanding of gene regulatory networks underlying the sulfate deficiency response in plants.

Sulfur (S) is an essential macronutrient for plants and its availability in soils is a relevant determinant for plant growth and development. Current regulatory policies aimed at reducing industrial S emissions and changes in agronomical practices have caused a decline in S contents in soils worldwide. Deficiency of sulfate - the primary form of S accessible to plants in soil - has adverse effects on both crop yield and nutritional quality. Therefore, recent research has increasingly focused on unraveling the molecular mechanisms through which plants detect and adapt to a limiting supply of sulfate. A significant part of these studies involves the use of omics technologies and has generated comprehensive catalogs of sulfate deficiency-responsive genes and processes, principally in Arabidopsis thaliana, with a few studies centering on crop species such as wheat, rice or members of the Brassica genus. Although we know that sulfate deficiency elicits an important reprogramming of the transcriptome, the transcriptional regulators orchestrating this response are not yet well understood. In this review, we summarize the knowledge on gene expression responses to sulfate deficiency and current efforts on the identification of transcription factors relevant for controlling this response. We further compare the transcriptional response and putative regulators between Arabidopsis thaliana and two relevant crop plants, rice and tomato, to gain insights into common mechanisms of response to sulfate deficiency.