Abstract
Whereas several mitochondrial/chloroplast pentatricopeptide repeat (PPR) proteins have been reported to regulate plant responses to abiotic stresses, no nucleus-localized PPR protein has been found to play role in these processes. In the present experiment, we provide evidence that a cytosol-nucleus dual-localized PPR protein SOAR1, functioning to negatively regulate abscisic acid (ABA) signaling in seed germination and postgermination growth, is a crucial, positive regulator of plant response to abiotic stresses. Downregulation of SOAR1 expression reduces, but upregulation of SOAR1 expression enhances, ABA sensitivity in ABA-induced promotion of stomatal closure and inhibition of stomatal opening, and plant tolerance to multiple, major abiotic stresses including drought, high salinity and low temperature. Interestingly and importantly, the SOAR1-overexpression lines display strong abilities to tolerate drought, salt and cold stresses, with surprisingly high resistance to salt stress in germination and postgermination growth of seeds that are able to potentially germinate in seawater, while no negative effect on plant growth and development was observed. So, the SOAR1 gene is likely useful for improvement of crops by transgenic manipulation to enhance crop productivity in stressful conditions. Further experimental data suggest that SOAR1 likely regulates plant stress responses at least partly by integrating ABA-dependent and independent signaling pathways, which is different from the ABI2/ABI1 type 2C protein phosphatase-mediated ABA signaling. These findings help to understand highly complicated stress and ABA signalling network.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-015-0327-9) contains supplementary material, which is available to authorized users.
Highlights
Terrestrial plant may suffer from various abiotic stresses during the whole life cycle, among which, salinity, drought and low temperature are major factors that restrict productivity
Downregulation of SOAR1 expression reduces, but upregulation of SOAR1 expression enhances, dehydration tolerance from detached leaves of the SOAR1-overexpression lines was relatively small compared with wild types, while this change resulted in significant increase in their drought tolerance
We observed that the stomata of an ABI2-overexpression line ABI2-OE that we generated previously (Sun et al 2011; Mei et al 2014) kept open even in the dark and exhibited strong abscisic acid (ABA)-insensitive phenotypes in ABA-induced promotion of stomatal closure and inhibition of stomatal opening (Fig. 1a), revealing that guard cell signaling in response to ABA was seriously lesioned in the ABI2OE line
Summary
Terrestrial plant may suffer from various abiotic stresses during the whole life cycle, among which, salinity, drought and low temperature are major factors that restrict productivity. The pgn mutant and PGN-overexpression lines (Laluk et al 2011), the ppr (Zsigmond et al 2008), ahg (Murayama et al 2012), slg (Yuan and Liu 2012), and slo (Zhu et al 2014) mutants showed hypersensitivity to salt or osmotic stress during germination and/or postgermination growth, while adult plants of the slo or slg mutants showed increased drought and/or salt tolerance (Yuan and Liu 2012; Zhu et al 2014) These data suggest a highly complicated mechanism by which these mitochondrial/ chloroplast PPRs regulate plant response to abiotic stresses, though it was proposed that they may regulate reactive oxygen species (ROS) homeostasis to be involved in stress responses or ABA signaling
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