The Effects of Co-Overexpression of the Arabidopsis Vacuolar Pyrophosphatase Gene AVP1 and the Protein Phosphatase 2a Catalytic Subunit 5 Gene PP2a-C5 Under Multi-Stress Conditions

Overview

Abiotic stresses such as drought, salt, and high temperatures cause significant losses in agricultural productivity worldwide. Global climate change will lead to an increased frequency of extreme weather events in many regions, which will pose even bigger challenges to food production in developing countries, where population growth often outpaces agricultural production. To continue feeding the world population, it is imperative to develop crops that can tolerate harsher conditions while maintaining yield and nutritional quality. Hence, many efforts have been made in the last 20 years in genetically modifying plants in order to make plants more tolerant to abiotic stress conditions. For example, the overexpression of the Arabidopsis protein phosphatase 2A catalytic subunit 5 gene (PP2A-C5) improves plant tolerance to several salts: NaCl, KCl, and KNO3. Also, the overexpression of the Arabidopsis thaliana vacuolar pyrophosphatase gene AVP1 and the co-overexpression of AVP1 and PP2A-C5 increase tolerance under a single stress of saline conditions. In nature, plants are often exposed to multiple stresses, and thus, it is imperative to develop crops that can tolerate multiple stresses simultaneously. In this study, a hypothesis that the co-overexpression of AVP1 and PP2A-C5 would increase tolerance under the stresses of drought plus salt when compared to wild-type, AVP1-overexpressing, and PP2A-C5 overexpressing plants was tested. A study of PP2A-C5 suggested that PP2A-C5 activates the activities of chloride channel proteins CLCa and CLCc, both antiporters, moving Clˉ and NO3ˉ into vacuoles, respectively, while moving a proton out. Since AVP1 is a proton pump that pumps protons into vacuoles, the activities of CLCa and CLCc depend on AVP1. Therefore, it was reasonable to postulate that the co-overexpression of AVP1 and PP2A-C5 might further improve activities of CLCa and CLCc, leading to higher tolerance to multiple stresses. Under low salt and drought stresses, there were no significant phenotypic or biomass differences, and all plants survived. Under high salt and drought stresses, the survival rate of AVP1/PP2A-C5 co-overexpressing plants was 63%, AVP1 overexpressing plants was 38%, PP2A-C5 overexpressing plants was 19%, and wild-type plants was 0%. Thus, the co-overexpression of AVP1 and PP2A-C5 significantly improved the survival rate under the combined stresses of drought and high salinity and may be a viable method to improve stress tolerance in crop plants. Additional experiments testing the co-overexpression of these genes in crops is warranted.