| Summary: | Siberian wildrye (<i>Elymus sibiricus</i> L.) is a salt-tolerant, high-quality forage grass that plays an important role in forage production and ecological restoration. Abscisic acid (ABA)-insensitive 5 (<i>ABI5</i>) is essential for the normal functioning of the ABA signal pathway. However, the role of <i>ABI5</i> from Siberian wildrye under salt stress remains unclear. Here, we evaluated the role of <i>Elymus sibiricus</i> L. abscisic acid-insensitive 5 (<i>EsABI5</i>) in the ABA-dependent regulation of the response of Siberian wildrye to salt stress. The open reading frame length of <i>EsABI5</i> isolated from Siberian wildrye was 1170 bp, and it encoded a 389 amino acid protein, which was localized to the nucleus, with obvious coiled coil areas. EsABI5 had high homology, with ABI5 proteins from <i>Hordeum vulgare</i>, <i>Triticum monococcum</i>, <i>Triticum aestivum</i>, and <i>Aegilops tauschii</i>. The conserved domains of EsABI5 belonged to the basic leucine zipper domain superfamily. EsABI5 had 10 functional interaction proteins with credibility greater than 0.7. <i>EsABI5</i> expression was upregulated in roots and leaves under NaCl stress and was upregulated in leaves and downregulated in roots under ABA treatment. Notably, tobacco plants overexpressing the <i>EsABI5</i> were more sensitive to salt stress, as confirmed by the determining of related physiological indicators. <i>EsABI5</i> expression affected the ABA and mitogen-activated protein kinase pathways. Therefore, <i>EsABI5</i> is involved in antisalt responses in these pathways and plays a negative regulatory role during salt stress.
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