Abstract
The Salt Overly Sensitive (SOS) signaling pathway is key in responding to salt stress in plants. SOS2, a central factor in this pathway, has been studied in non-halophytes such as Arabidopsis and rice, but has so far not been reported in the halophyte Nitraria tangutorum. In order to better understand how Nitraria tangutorum acquires its tolerance for a high salt environment, here, the NtSOS2 was cloned from Nitraria tangutorum, phylogenetic analyses showed that NtSOS2 is homologous to the SOS2 of Arabidopsis and rice. Gene expression profile analysis showed that NtSOS2 localizes to the cytoplasm and cell membrane and it can be induced by salt stress. Transgenesis experiments showed that exogenous expression of NtSOS2 reduces leaf mortality and improves the germination rate, biomass and root growth of Arabidopsis under salt stress. Also, exogenous expression of NtSOS2 affected the expression of ion transporter-related genes and can rescue the phenotype of sos2-1 under salt stress. All these results revealed that NtSOS2 plays an important role in plant salt stress tolerance. Our findings will be of great significance to further understand the mechanism of salt tolerance and to develop and utilize molecular knowledge gained from halophytes to improve the ecological environment.
Highlights
Soil salinization has become a major constraint to the sustainable development of the ecological environment, more than 20% of arable land suffered from soil salinization (Shrivastava and Kumar, 2015; Rui and Ricardo, 2017) and a trend for ever increasing salinization has been observed (Cuevas et al, 2019; Singh, 2021)
In order to clone SOS2 of Nitraria tangutorum, the SOS2 protein sequences from rice and Arabidopsis were compared to our unpublished transcriptome data using the NCBI blastp program
The NtSOS2 protein sequence was aligned with the Calcineurin B-like proteins-interacting protein kinases (CIPKs) gene family of Arabidopsis and rice to construct a phylogenetic tree, and the results showed that NtSOS2, AtCIPK24, and OsCIPK24 are distributed on one branch (Figure 2)
Summary
Soil salinization has become a major constraint to the sustainable development of the ecological environment, more than 20% of arable land suffered from soil salinization (Shrivastava and Kumar, 2015; Rui and Ricardo, 2017) and a trend for ever increasing salinization has been observed (Cuevas et al, 2019; Singh, 2021). The main reason why plants have difficulty in living in salinized soil is that they are subjected to abiotic stress, which will lead to osmotic stress and ion toxicity under salt stress (Liang et al, 2018; Arif et al, 2020). When plants subjected to stress, Ca2+ concentration increases and activates protein kinases by calmodulin induce a series of cellular reactions to make plants adapt to or reduce the damage caused by salt stress (Villalobo and Berchtold, 2020). Plant protein kinases (a kind of phosphotransferase) participate in the process of plant stress resistance signaling and play an important role when plants suffer from salt damage and drought stress (Yip Delormel and Boudsocq, 2019; Chen et al, 2021). The SOS2 C-terminal regulatory region contains a conserved NAF/FISL motif that interacts with the Ca2+ binding protein SOS3/CBL4 to form a binary complex, after which they integrate into the plasma membrane and activate the SOS1 gene (Quintero et al, 2002; Qiu et al, 2004; Yang et al, 2009)
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