Abstract
The calcium-sensing receptor (CaS), which is localized in the chloroplasts, is a crucial regulator of extracellular calcium-induced stomatal closure in Arabidopsis. It has homologs in Oryza sativa and other plants. These sequences all have a rhodanese-like protein domain, which has been demonstrated to be associated with specific stress conditions. In this study, we cloned the Oryza sativa calcium-sensing receptor gene (OsCAS) and demonstrated that OsCAS could sense an increase of extracellular Ca2+ concentration and mediate an increase in cytosolic Ca2+ concentration. The OsCAS gene was transformed into an Arabidopsis CaS knockout mutant (Salk) and overexpressed in the transgenic plants. OsCAS promoted stomatal closure. We screened homozygous transgenic Arabidopsis plants and determined physiological indices such as the oxidative damage biomarker malondialdehyde (MDA), relative membrane permeability (RMP), proline content, and chlorophyll fluorescence parameters, after 21 days of drought treatment. Our results revealed lower RMP and MDA contents and a higher Proline content in transgenic Arabidopsis plants after drought stress, whereas the opposite was observed in Salk plants. With respect to chlorophyll fluorescence, the electron transport rate and effective PSII quantum yield decreased in all lines under drought stress; however, in the transgenic plants these two parameters changed fewer and were higher than those in wild-type and Salk plants. The quantum yield of regulated energy dissipation and nonregulated energy dissipation in PSII were higher in Salk plants, whereas these values were lower in the transgenic plants than in the wild type under drought stress. The above results suggest that the transgenic plants showed better resistance to drought stress by decreasing damage to the cell membrane, increasing the amount of osmoprotectants, and maintaining a relatively high photosynthetic capacity. In conclusion, OsCAS is an extracellular calcium-sensing receptor that helps to compensate for the absence of CaS in Arabidopsis and increases the drought stress tolerance of transgenic plants.
Highlights
Water is vital for plant growth and development, and water deficit stress, permanent or temporary, limits the growth and distribution of natural vegetation and the performance of cultivated plants to a greater extent than any other environmental factor [1]
We found that Oryza sativa calcium-sensing receptor gene (OsCAS) overexpression in the transgenic plants promoted stomatal closure in the absence of external Ca2+ (Fig 3)
Arabidopsis thaliana is often used as a plant model to study the physiological and biochemical characteristics of plants
Summary
Water is vital for plant growth and development, and water deficit stress, permanent or temporary, limits the growth and distribution of natural vegetation and the performance of cultivated plants to a greater extent than any other environmental factor [1]. Synthesis of stress proteins is a ubiquitous response to cope with prevailing stressful conditions, including water deficit [6]. Photosynthetic capacity is progressively reduced by stomatal closure in response to water deficit stress. Chlorophyll fluorescence measurements have been widely used to study the response of plants to environmental stress [8,10,11,12]. Y(NPQ), the quantum yield of regulated energy dissipation in PSII, reflects the downregulation of PSII as a protective mechanism against excess light intensity. Y(NO), the quantum yield of non-regulated energy dissipation in PSII, is indicative of plants having serious problems coping with incident radiation [13,14,15]. The electron transport rate (ETR) can be measured using pulse amplitude-modulated (PAM) fluorimetry during rapid light curve experiments and used to assess the physiological state of the plant [16,17]
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