Identification and differential expression of two isogenes encoding 1-deoxy-D-xylulose 5-phosphate reductoisomerase in Glycine max

Plant 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) were considered to be encoded by single copy. In this study, we successfully isolated two DXR isogenes, designated GmDXR1 and GmDXR2, from soybean. The multicopy nature of DXRs in soybean was supported by Southern blot. Alignment of the two GmDXRs showed the presence of the N-terminal transit peptide for plastids, the conserved cleavage site, proline-rich region, and the NADPH-binding motif. Phylogenetic analysis revealed GmDXR1 and GmDXR2 belonged to different branches of angiosperm DXRs clusters. Expression pattern analysis indicated that GmDXR1 was expressed in all analyzed organs except the pod walls, with the highest level in seeds, whereas no message was detected for GmDXR2. In response to heat stress, GmDXR1 showed declined transcript levels in the experiments; in contrast, GmDXR2 was highly responsive, with mRNA accumulation peaking at 6 h after treatment. We also demonstrated that both GmDXRs were localized in chloroplasts. Overexpression of GmDXRs induced increased contents of various isoprenoids (chlorophyll, carotenoids, and gibberellins), but with reduced level of ABA, indicating that GmDXRs participate in the control of differential isoprenoid biosynthesis of the MEP pathway. This work provides a new insight into the wide presence of multicopies of DXR enzyme in plants.