Plants are subject to a number of stresses, with some aggravated by the pressures of climate change. This has immediate implications for plant health and ultimately, food security. With an increasing amount of arable land under drought stress and a growing global population, there is a growing need for the cultivation of plants that are drought-tolerant. It is therefore critical to understand the processes that determine a plant’s susceptibility or tolerance to stresses such as drought at a molecular level because it can contribute to the breeding of plants that can survive various stresses. 

Research undertaken as part of a PhD study by Molly Malefo at the University of Pretoria’s Department of Plant and Soil Sciences and Forestry and Agricultural Biotechnology Institute (FABI) sheds more light on the role of protease inhibitors in plants under drought stress. This is detailed in “Investigating the role of Bowman-Birk serine protease inhibitor in Arabidopsis plants under drought stress” published in Plant Physiology and Biochemistry. According to the authors, protein inhibitors play an important role in abiotic stress tolerance. Protease inhibitors such as Bowman-Birk inhibitors (BBI) regulate the expression of enzymes that facilitate the breakdown of protein in plants. Though important for cellular functions, an overexpression of these enzymes can be damaging to plants and therefore needs regulation. 

In this study, four-week-old Arabidopsis thaliana plants overexpressing the BBIgene from maize were generated and subjected to drought stress by withholding water for nine days. In Arabidopsis, serine protease inhibitors were noted to increase salt, drought, oxidation and cold tolerance. Harvested plant material was used for physiological and biochemical analysis. The transgenic lines exhibited normal growth after nine days of drought as compared to the wild-type, wrote the authors. 

“In our study, BBI-gene expressing plants displayed more tolerance to drought stress when compared to the wild-type, which showed wilting symptoms at nine days of water withdrawal while transgenic lines possessed more turgid leaves as a result of the higher relative water content observed,” wrote the authors. Relative water content is a signifier of drought tolerance in plants. Furthermore, the authors showed that there was higher antioxidant activity in the transgenic lines compared to the wild-type. Antioxidants are known to play an important role against drought stress. 

Ms Malefo undertakes this study under the supervision of Dr Eugene Makgopa and Dr Bridget Crampton. As FABI supports the International Year of Plant Health in 2020, this study highlights the need to promote research that contributes to plant health in Africa and the world. 

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