Transgenic Indian mustard overexpressing selenocysteine lyase or selenocysteine methyltransferase exhibit enhanced potential for selenium phytoremediation under field conditions

Two new transgenic Indian mustard [Brassica juncea (L.) Czern.] lines were tested under field conditions for their ability to accumulate selenium (Se) from Se- and boron-contaminated saline sediment. The transgenic lines overexpress genes encoding the enzymes selenocysteine lyase (cpSL) and selenocysteine methyltransferase (SMT), respectively. In the first Spring planting, cpSL, SMT, and wildtype plants (WT) were compared, while SMT and WT were compared in a second, Fall planting. In the Spring planting, shoots of the cpSL transgenic plants accumulated 2-fold more Se (p < 0.01), had 1.8 times higher leaf Se concentrations (p < 0.01), and grew better on contaminated soil than WT. The SMT plants had a 1.7-fold higher leaf Se concentration than WT (p < 0.05). In the Fall planting, the SMT transgenic plants accumulated 1.6-fold more Se in their shoots than WT (p < 0.01) with Se concentrations being higher in both leaves and stems. These results conclusively demonstrate that cpSL and SMT transgenic lines have significantly greater Se phytoremediation potential than wildtype Indian mustard. Further, this study confirms the importance of field testing for evaluating future transgenic lines.