Soybean seeds overexpressing asparaginase exhibit reduced protein concentration.

Pandurangan, S., Pajak, A., Rintoul, T.L., Beyaert, R.P., Hernández-Sebastià, C., Brown, D.C.W., and Marsolais, F. (2015). "Soybean seeds overexpressing asparaginase exhibit reduced protein concentration.", Physiologia Plantarum, 152(2), pp. 126-137. doi : 10.1111/ppl.12341  Access to full text

Abstract

In soybean seed, a correlation has been observed between the concentration of free asparagine at mid-maturation and protein concentration at maturity. In this study, a Phaseolus vulgaris K+-dependent asparaginase cDNA, PvAspG2, was expressed in transgenic soybean under the control of the embryo specific promoter of the β-subunit of β-conglycinin. Three lines were isolated having high expression of the transgene at the transcript, protein and enzyme activity levels at mid-maturation, with a 20- to 40-fold higher asparaginase activity in embryo than a control line expressing β-glucuronidase. Increased asparaginase activity was associated with a reduction in free asparagine levels as a percentage of total free amino acids, by 11–18%, and an increase in free aspartic acid levels, by 25–60%. Two of the lines had reduced nitrogen concentration in mature seed as determined by nitrogen analysis, by 9–13%. Their levels of extractible globulins were reduced by 11–30%. This was accompanied by an increase in oil concentration, by 5–8%. The lack of change in nitrogen concentration in the third transgenic line was correlated with an increase in free glutamic acid levels by approximately 40% at mid-maturation.

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