title: Cadmium exposure and sulfate limitation reveal differences in the transcriptional control of three sulfate transporter (Sultr1;2) genes in Brassica juncea.
abstract: BACKGROUND
  Cadmium (Cd) exposure and sulfate limitation induce root sulfate uptake to meet the metabolic demand for reduced sulfur. Although these responses are well studied, some aspects are still an object of debate, since little is known about the molecular mechanisms by which changes in sulfate availability and sulfur metabolic demand are perceived and transduced into changes in the expression of the high-affinity sulfate transporters of the roots. The analysis of the natural variation occurring in species with complex and highly redundant genome could provide precious information to better understand the topic, because of the possible retention of mutations in the sulfate transporter genes.
  
  
  RESULTS
  The analysis of plant sulfur nutritional status and root sulfate uptake performed on plants of Brassica juncea - a naturally occurring allotetraploid species - grown either under Cd exposure or sulfate limitation showed that both these conditions increased root sulfate uptake capacity but they caused quite dissimilar nutritional states, as indicated by changes in the levels of nonprotein thiols, glutathione and sulfate of both roots and shoots. Such behaviors were related to the general accumulation of the transcripts of the transporters involved in root sulfate uptake (BjSultr1;1 and BjSultr1;2). However, a deeper analysis of the expression patterns of three redundant, fully functional, and simultaneously expressed Sultr1;2 forms (BjSultr1;2a, BjSultr1;2b, BjSultr1;2c) revealed that sulfate limitation induced the expression of all the variants, whilst BjSultr1;2b and BjSultr1;2c only seemed to have the capacity to respond to Cd.
  
  
  CONCLUSIONS
  A novel method to estimate the apparent kM for sulfate, avoiding the use of radiotracers, revealed that BjSultr1;1 and BjSultr1;2a/b/c are fully functional high-affinity sulfate transporters. The different behavior of the three BjSultr1;2 variants following Cd exposure or sulfate limitation suggests the existence of at least two distinct signal transduction pathways controlling root sulfate uptake in dissimilar nutritional and metabolic states.
authors.forename: Clarissa
authors.initials: C
authors.lastname: Lancilli
authors.forename: Barbara
authors.initials: B
authors.lastname: Giacomini
authors.forename: Giorgio
authors.initials: G
authors.lastname: Lucchini
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Davidian
authors.forename: Maurizio
authors.initials: M
authors.lastname: Cocucci
authors.forename: Gian Attilio
authors.initials: GA
authors.lastname: Sacchi
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia, Università degli Studi di Milano, 20133 Milano, Italy. fabio.nocito@unimi.it.
authors.forename: Fabio Francesco
authors.initials: FF
authors.lastname: Nocito
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics; D018533:Biomass; D002104:Cadmium / Q000633:toxicity*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009149:Mustard Plant / Q000187:drug effects / Q000235:genetics*; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015183:Restriction Mapping; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000254:growth & development; D013431:Sulfates / Q000378:metabolism / Q000494:pharmacology*; D013455:Sulfur / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D013431:Sulfates; D002104:Cadmium; D013455:Sulfur