Isolation and characterization of salt overly sensitive family genes in spinach

Authors: ZHAO, CHAOYANG - University Of California; WILLIAM, DAVID - University Of California; Sandhu, Devinder

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2020
Publication Date: 5/16/2020
Publication URL: https://handle.nal.usda.gov/10113/7019858
Citation: Zhao, C., William, D., Sandhu, D. 2021. Isolation and characterization of Salt Overly Sensitive family genes in spinach. Physiologia Plantarum. 171(4):520-532. https://doi.org/10.1111/ppl.13125.
DOI: https://doi.org/10.1111/ppl.13125

Interpretive Summary: To survive, all organisms must maintain the cellular balance and an internal stability with regards to many factors including temperature, pH, and ions. Exposure of an organism to abiotic stresses such as high salinity may lead to the excessive accumulation of certain molecules causing balance disruption or failure. Under high salinity environment, Salt Overly Sensitive (SOS) pathway is critical in extruding Na+ from plant cells. SOS pathway in Arabidopsis, a model plant, is comprised of SOS1, SOS2 and SOS3 proteins. The objective of this investigation was to investigate if SOS pathway is conserved in spinach, a member of Amaranthaceae family. In addition, we wanted to understand how SOS pathway-related genes evolved in Amaranthaceae species. We conducted genome-wide identification and family analyses of SOS1-, SOS2-, and SOS3-like genes on four Amaranthaceae species. Most Amaranthaceae genes identified exhibited orthologous relationships with Arabidopsis and/or rice. We identified single spinach proteins for each SOS1, SOS2, and SOS3. Protein-protein interaction assay showed that SOS3 and SOS2 interact with each other, however SOS2 and SOS1 do not, suggesting some differences in modes of action between Spinach and Arabidopsis. Spinach SOS3 gene was expressed at higher levels in roots emphasizing its more critical role in roots. Spinach SOS3 was upregulated under salinity in both leaves and roots. These results are important to spinach breeders and geneticists to develop new salt-tolerant spinach varieties, which will allow farmers to increase spinach yield in regions where quality of water/soil is not suitable.

Technical Abstract: The Salt Overly Sensitive (SOS) pathway regulates intracellular sodium ion homeostasis as a salt-stress response in plants. This pathway involves three main genes designated as SOS1, SOS2, and SOS3, which are members of the Na+/H+ exchanger (NHX), CBL-interacting protein kinase (CIPK), and Calcineurin B-like (CBL) gene families, respectively. To identify and characterize SOS genes in spinach (Spinacia oleracea), a species of the Amaranthaceae family, we conducted genome-wide identification and phylogenetic analyses of NHX, CIPK, and CBL genes from four Amaranthaceae species, Arabidopsis, and rice. Most Amaranthaceae genes exhibited orthologous relationships with Arabidopsis and/or rice, except a clade of Vac-type Amaranthaceae NHX genes. Phylogenetic analyses also revealed gene gain/loss events in Amaranthaceae species and the intron-less to intron-rich evolution of CIPK genes. A bacterial protein-rooted CIPK tree allowed naming most of the phylogenetic clades based on their evolutionary history. Single S. oleracea (So) SOS1, SOS2, and SOS3 proteins were identified. Direct protein–protein interaction was observed between SoSOS2 and SoSOS3 but not between SoSOS2 and SoSOS1 based on yeast two-hybrid assay. This may suggest distinct modes of action of spinach SOS proteins compared to Arabidopsis SOS proteins. Unlike SoSOS1 and SoSOS2, which were expressed at similar or higher levels in leaves than roots, SoSOS3 expression was significantly higher in roots than leaves, suggesting its greater importance in roots. The expression of SoSOS3 was upregulated in both roots and leaves under salinity compared to the control; however, SoSOS1 was only upregulated in roots. Thus, this study demonstrated the conservation of SOS pathway genes in spinach and also highlighted the complexity of SOS signaling in Amaranthaceae species.