Several sub-projects in this field aim to increase our understanding of the inhibition and regulation of cysteine protease activity by plant cystatins. This includes the role of cysteine proteases and cystatins during nodule development and senescence in soybean as well as the possibility of using cystatins to increase abiotic stress resistance in nodules. A further project relates to the inhibition of insect digestive proteases by plant cystatins and their potential for use in developing insect resistant crops.

We study the function and importance of specific amino acids in the cystatin proteins using techniques such as homology modelling and protein-protein docking to study and predict specific interactions in silico. We also change specific amino acids in the proteins through site-directed mutagenesis in order to study their effect on the inhibition potential of the modified cystatins in vitro. Selected cystatins have also been recombinantly expressed in various plants to evaluate their role in vivo particularly in repressing senescence and protein degradation.

New Publications

Juan Vorster, Chris Cullis, Karl Kunert. (2019) Plant Vacuolar Processing Enzymes. Frontiers in Plant Science :00497. 10.3389/fpls.2019.00479 PDF
Cullis C, Lawler DW, Chimwamurombe P, Kunert K, Bbebe N, Vorster J. (2019) Development of marama bean, an orphan legume, as a crop. Food and Energy Security e00164:1-12. 10.1002/fes3.164 PDF
NM Okumu, BJ Vorster, CF Reinhardt. (2019) Growth-stage and temperature influence glyphosate resistance in Conyza bonariensis (L.) Cronquist.. South African Journal of Botany 121:248-256. 10.1016/j.sajb.2018.10.034 PDF
Cristopher Cullis, Percy Chimwamurombe, Nigel Barker, Karl Kunert, Juan Vorster. (2018) Orphan Legumes Growing in Dry Environments: Marama Bean as a Case Study. Frontiers in Plant Science 9:11999. 10.3389/fpls.2018.01199 PDF
Magdeleen Cilliers, Stefan van Wyk, Phillipus van Heerden, Karl Kunert, Juan Vorster. (2018) Identification and changes of the drought-induced cysteine protease transcriptome in soybean (Glycine max) root nodules. Journal of Experimental and Environmental Botany 148:59-69. 10.1016/j.envexpbot.2017.12.005
Priyen Pillay, Karl Kunert, Eugene Makgopa, Chris Cullis, Juan Vorste. (2016) Agroinfiltration contributes to VP1 recombinant protein degradation. Bioengineered 7(6):459-477. 10.1080/21655979.2016.1208868 PDF
Foyer CH, Lam H-M, Nguyen HT, Siddique KHM, Varshney RK, Colmer TD, Cowling W, Bramley H, Mori TA, Hodgson JM, Cooper JW, Miller AJ, Kunert K, Vorster J, Cullis C, Ozga JA, Wahlqvist ML, Liang Y, Shou H, Shi K, Yu J, Fodor N, Kaiser BN, Wong F-L, Valliyodan B, Considine MJ. (2016) Neglecting legumes has compromised human health and sustainable food production. Nature Plants 2:16112. 10.1038/nplants.2016.112
Pillay P, Kunert KJ, van Wyk S, Makgopa ME, Cullis CA, Vorster BJ. (2016) Agroinfiltration contributes to VP1 recombinant protein degradation. Bioengineered 7(6):459-477. 10.1080/21655979.2016.1208868
Kunert K, Vorster BJ, Fenta BA, Kibido T, Dionisio G, Foyer CH. (2016) Drought stress responses in soybean roots and nodules. Frontiers in Plant Science 7(1015) 10.3389/fpls.2016.01015 PDF
Sapountzis P, de Verges J, Rousk K, Cilliers M, Vorster BJ, Poulsen M. (2016) Potential for Nitrogen Fixation in the Fungus-Growing Termite Symbiosis. Frontiers in Microbiology 7:1993. 10.3389/fmicb.2016.01993 PDF
Naidoo SIM, Laurie SM, Odeny DA, Vorster BJ, Mphela WM, Greyling MM, Crampton BG. (2016) Genetic analysis of yield and flesh colour in sweetpotato. African Crop Science Journal 24(1):61-73. 10.4314/acsj.v24i1.5 PDF
Sainsbury F, Jutras PV, Vorster J, Goulet MC , Michaud D. (2016) A Chimeric Affinity Tag for Efficient Expression and Chromatographic Purification of Heterologous Proteins from Plants. Frontiers in Plant Science 7:141. 10.3389/fpls.2016.00141
Van Wyk SG, Kunert KJ, Cullis CA, Pillay P, Makgopa ME, Schluter U , Vorster BJ. (2016) The future of cystatin engineering. Plant Science 246:119-127. 10.1016/j.plantsci.2016.02.016 PDF
van Wyk SG, Du Plessis M, Cullis CA, Kunert KJ, Vorster BJ. (2014) Cysteine protease and cystatin expression and activity during soybean nodule development and senescence. BMC Plant Biology 14(294) 10.1186/s12870-014-0294-3
Pillay P, Schlüter U, van Wyk S, Kunert KJ, Vorster BJ. (2014) Proteolysis of recombinant proteins in bioengineered plant cells. Bioengineered 5(1):15-20. 10.4161/bioe.25158
Vorster BJ, Schlüter U, du Plessis M, van Wyk S, Makgopa ME, Ncube I, Quain MD, Kunert K, Foyer CH. (2013) The Cysteine Protease – Cysteine Protease Inhibitor System Explored in Soybean Nodule Development. Agronomy 3(3):550-570. 10.3390/agronomy3030550
Vorster B, Schlüter U, du Plessis M, van Wyk S, Makgopa M, Ncube I, Quain M, Kunert K, Foyer C. (2013) The cysteine protease–cysteine protease inhibitor system explored in soybean nodule development. Agronomy 3(3):550-570. 10.3390/agronomy3030550
Mphangwe NIK, Vorster J, Steyn JM, Nyirenda HE, Taylor NJ, Apostolides Z. (2013) Screening of Tea (Camellia sinensis) for Trait-Associated Molecular Markers. Applied Biochemistry and Biotechnology 171:437-449. 10.1007/s12010-013-0370-4
Vorster BJ, Schlüter U, du Plessis M, van Wyk S, Makgopa M, Ncube I, Quain M, Kunert KJ, Foyer C. (2013) The Cysteine Protease–Cysteine Protease Inhibitor System Explored in Soybean Nodule Development. Agronomy 3(3):550-570.
Kunert KJ, Okole B, Vorster BJ, Brewin NJ, Cullis CA. (2012) A general model for training the next generation of biotechnology entrepreneurs based on recent experience of USA-UK-South Africa collaborations. Journal of Commercial Biotechnology 18:62-66. 10.5912/jcb.525
Pillay P, Kibido T, Du Plessis M, Van der Vyver C, Beyene G, Vorster BJ, Kunert KJ, Schlueter U. (2012) Use of Transgenic Oryzacystatin-I-Expressing Plants Enhances Recombinant Protein Production. Applied Biochemistry and Biotechnology 168(6):1608-1620. 10.1007/s12010-012-9882-6
Sainsbury F, Rheaume A-J, Goulet M-C, Vorster J, Michaud D. (2012) Discrimination of Differentially Inhibited Cysteine Proteases by Activity-Based Profiling Using Cystatin Variants with Tailored Specificities. Journal of Proteome Research 11:5983-5993. 10.1021/pr300699n
Afiukwa CA, Kunert KJ, Vorster J, Cullis CA, Ubi BE. (2011) Microsatellite association with seed protein content and flowering time in Nigerian cowpea cultivars. African Journal of Biotechnology 10:18057-18064. 10.5897/AJB10.2537
Van der Vyver C, Vorster BJ, Kunert KJ, Cullis CA. (2011) Analysis of radiation-induced genome alterations in Vigna unguiculata. Research and Reports in Biology 2:89-99. 10.2147/RRB.S22790
Benchabane M, Schluter U, Vorster J, Goulet M, Michaud D. (2010) Plant cystatins. Biochimie 92(11):1657-1666. 10.1016/j.biochi.2010.06.006
Khalf M, Goulet C, Vorster BJ, Brunelle F, Anguenot R, Fliss I, Michaud D. (2010) Tubers from potato lines expressing a tomato Kunitz protease inhibitor are substantially equivalent to parental and transigenic controls. Plant Biotechnology Journal 8(2):155-169. 10.1111/j.1467-7652.2009.00471.x
Kiggundu A, Muchwezi J, Van der Vyver C, Viljoen A, Vorster BJ, Schluter U, Kunert KJ, Michaud D. (2010) Deleterious effects of plant cystatins against the Banana weevil Cosmopolites sordidus. Archives of Insect Biochemistry and Physiology 73(2):87-105. 10.1002/arch.20342
Schluter U, Benchabane M, Munger A, Kiggundu A, Vorster J, Goulet M, Cloutier C, Michaud D. (2010) Recombinant protease inhibitors for herbivore pest control: a multitrophic perspective. Journal of Experimental Botany 61(15):4169-4183. 10.1093/jxb/erq166
Cullis CA, Vorster BJ, van der Vyver C, Kunert KJ. (2009) Transfer of genetic material between the chloroplast and nucleus: how is it related to stress in plants?. Annals of Botany 103(4):625-633. 10.1093/aob/mcn173
Kunert K, Vorster J, Bester C, Cullis C, Rajasekaran K, Jacks T, Finley J. 2002. DNA microchip technology in the plant tissue culture industry. In: Crop Biotechnology, ACS Symposium Series, Vol. 829. American Chemical Society, USA, pp 86-96.