Abstract
Overexpression of abscisic acid (ABA) receptors has been reported to enhance drought tolerance, but also to cause stunted growth and decreased crop yield. Here, we constructed transgenic rice for all monomeric ABA receptors and observed that only transgenic rice over-expressing OsPYL/RCAR7 showed similar phenotype with wild type, without total yield loss when grown under normal growth condition in a paddy field. Even though transgenic rice over-expressing OsPYL/RCAR7 showed neither an ABA-sensitivity nor an osmotic stress tolerance in plate assay, it showed drought tolerance. We investigated the ABA-dependent interaction with OsPP2CAs and ABA signaling induction by OsPYL/RCAR7. In yeast two hybrid assay, OsPYL/RCAR7 required critically higher ABA concentrations to interact with OsPP2CAs than other ABA receptors, and co-immunoprecipitation assay showed strong interaction under ABA treatment. When ABA-responsive signaling activity was monitored using a transient expression system in rice protoplasts, OsPYL/RCAR7 had the lowest ABA-responsive signaling activity as compared with other ABA receptors. OsPYL/RCAR7 also showed weak suppression of phosphatase activity as compared with other ABA receptors in vitro. Transcriptome analysis of transgenic rice over-expressing OsPYL/RCAR7 suggested that only a few genes were induced similar to control under without exogenous ABA, but a large number of genes was induced under ABA treatment compared with control. We conclude that OsPYL/RCAR7 is a novel functional ABA receptor that has low ABA signaling activity and exhibits high ABA dependence. These results lay the foundation for a new strategy to improve drought stress tolerance without compromising crop growth.
Highlights
Rice is a staple crop that provides a major source of calories for more than 2 billion people around the world, in Asian countries
According to Miao and co-worker’s report (2018), the knock-out lines of abscisic acid (ABA) receptors showed an increase in growth under paddy field conditions, suggesting that each ABA receptor affects plant growth differently
Overexpression of TaPYL4 showed the increase of ABA sensitivity, resulting in higher water use efficiency (WUE) and drought tolerance in wheat [38]
Summary
Rice is a staple crop that provides a major source of calories for more than 2 billion people around the world, in Asian countries. Distinct mutant phenotype with higher growth rate was shown for class I mutation and no significant phenotype was recorded for class II mutants These differences among the ABA receptors suggest the possibility of their functional variation between different classes. Apart from the mutant analyses, earlier studies have shown that gain-of-function mutations of ABA receptors negatively regulate plant growth and positively enhance the osmotic stress tolerance and sensitivity to ABA [6,25,28,34,36]. The regulation of water use efficiency (WUE) in wheat by alteration in the ABA receptors provides another scenario of fine tuning the ABA receptors expression in plants and developing osmotic stress tolerant crops without compromising the total yield [37,38]. This work provides a new strategy to develop abiotic stress-tolerant crops without yield penalty by introducing stress tolerance mechanisms that are not activated under normal or mild stress conditions, but function under harsh stress condition
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