Analysis of sulfur and selenium assimilation in Astragalus plants with varying capacities to accumulate selenium.
Several Astragalus species have the ability to hyperaccumulate selenium (Se) when growing in their native habitat. Given that the biochemical properties of Se parallel those of sulfur (S), we examined the activity of key S assimilatory enzymes ATP sulfurylase (ATPS), APS reductase (APR), and serine acetyltransferase (SAT), as well as selenocysteine methyltransferase (SMT), in eight Astragalus species with varying abilities to accumulate Se. Se hyperaccumulation was found to positively correlate with shoot accumulation of S-methylcysteine (MeCys) and Se-methylselenocysteine (MeSeCys), in addition to the level of SMT enzymatic activity. However, no correlation was observed between Se hyperaccumulation and ATPS, APR, and SAT activities in shoot tissue. Transgenic Arabidopsis thaliana overexpressing both ATPS and APR had a significant enhancement of selenate reduction as a proportion of total Se, whereas SAT overexpression resulted in only a slight increase in selenate reduction to organic forms. In general, total Se accumulation in shoots was lower in the transgenic plants overexpressing ATPS, PaAPR, and SAT. Root growth was adversely affected by selenate treatment in both ATPS and SAT overexpressors and less so in the PaAPR transgenic plants. Such observations support our conclusions that ATPS and APR are major contributors of selenate reduction in planta. However, Se hyperaccumulation in Astragalus is not driven by an overall increase in the capacity of these enzymes, but rather by either an increased Se flux through the S assimilatory pathway, generated by the biosynthesis of the sink metabolites MeCys or MeSeCys, or through an as yet unidentified Se assimilation pathway.
Sors
Thomas G
TG
Center for Plant Environmental Stress Physiology, 1165 Horticulture Building, Purdue University, West Lafayette, IN 47907, USA.
Ellis
Danielle R
DR
Na
Gun Nam
GN
Lahner
Brett
B
Lee
Sangman
S
Leustek
Thomas
T
Pickering
Ingrid J
IJ
Salt
David E
DE
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D027883:Astragalus Plant / Q000145:classification / Q000201:enzymology / Q000378:metabolism*; D001693:Biological Transport, Active; D015870:Gene Expression; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012643:Selenium / Q000378:metabolism*; D013045:Species Specificity; D013455:Sulfur / Q000378:metabolism*
D010940:Plant Proteins; D013455:Sulfur; D012643:Selenium