Molecular and physiological characterization of transgenic soybean (Glycine max) over-expressing oryzacystatin-I (OCI) in their root nodules

Abstract

Pre-mature nodule senescence is a naturally occurring process that often has a negative impact on plant growth and development. Nodule senescence is regulated by a class of enzymes known as cysteine proteases. In this study, transgenic soybean (Glycine max) were investigated in order to determine whether nodule senescence can be prolonged by reducing the activity of cysteine proteases. Transgenic lines over-expressing a cysteine protease inhibitor (oryzacystatin-I) in root nodules were characterized under different growth conditions. Differential transgene expression occurred in transgenic lines. The presence of OCI was detected by determining cysteine protease activity using a fluoremetric assay which utilizes a fluorogenic cysteine protease substrate. Under well-watered conditions, OCI did lower cysteine protease activity in transgenic plants and also improved the growth rate of trifoliate leaves. The most potent effects of OCI were observed when plants were less than 9 weeks old. This was maybe due to a spike of OCI expression in nodules. Although cysteine protease activity was also lowered under drought conditions, detectable effects of OCI on plant biology were difficult to characterize in drought-treated transgenic lines. Overall, the results of this study demonstrated that organ-specific over-expression of a cysteine protease inhibitor can alter certain plant functionalities that are related to the activity of those cysteine proteases. Future work will focus on determining OCI sensitive proteases and the respectable pathways which they are involved in.