Under stress, plant cellular proteins can be oxidized at multiple amino acid residues causing protein dysfunction that may lead to reduced viability of plants. One of the oxidized amino acids, methionine sulfoxide (MetO), was frequently found in stressed plants. In soybeans, there are five methionine-R-sulfoxide reductases (GmMSRBs) responsible for the reduction of Met-R-O, one of the two MetO isomers. To identify GmMSRBs that may be involved in repairing Met-R-O under different stress conditions, we determined transcript levels of GmMSRBs in various tissues subjected to dehydration/drought, high salinity, and abscisic acid (ABA) during different developmental stages. Under normal conditions, expression levels were the highest in leaves, followed by roots, and lowest in seeds and seed pods. Among the GmMSRBs, transcripts of GmMSRB1 in the leaves were the highest; at the same time, GmMSRB5 was shown to be expressed at the lowest levels. Expression of GmMSRBs were then determined under stress-inducing conditions. In seedling shoots, GmMSRB2 and GmMSRB5 were expressed in response to drought conditions. In vegetative V6 trifolia, only GmMSRB3 was induced under drought. In reproductive R2 trifolia, the expression of GmMSRB2 and GmMSRB5 were induced by drought. However, expressions of all five GmMSRBs in the roots were not affected by the any stress-inducing conditions. Under salt stress, GmMSRB1 was down-regulated in seedling shoots and GmMSRB5 was up-regulated in seedling roots. Treatment with ABA did not affect the transcript levels of any GmMSRBs in seedling shoots. However, this treatment up-regulates GmMSRB2 in seedling roots. Our data suggested that with the exception of GmMSRB4, all the remaining four GmMSRBs play a role in soybean responses to multiple environmental stresses and that genes encoding cytosolic and plastidic GmMSRBs respond differently under stress.
