Abstract
Expansins are key regulators of cell-wall extension and are also involved in the abiotic stress response. In this study, we evaluated the function of OsEXPA7 involved in salt stress tolerance. Phenotypic analysis showed that OsEXPA7 overexpression remarkably enhanced tolerance to salt stress. OsEXPA7 was highly expressed in the shoot apical meristem, root, and the leaf sheath. Promoter activity of OsEXPA7:GUS was mainly observed in vascular tissues of roots and leaves. Morphological analysis revealed structural alterations in the root and leaf vasculature of OsEXPA7 overexpressing (OX) lines. OsEXPA7 overexpression resulted in decreased sodium ion (Na+) and accumulated potassium ion (K+) in the leaves and roots. Under salt stress, higher antioxidant activity was also observed in the OsEXPA7-OX lines, as indicated by lower reactive oxygen species (ROS) accumulation and increased antioxidant activity, when compared with the wild-type (WT) plants. In addition, transcriptional analysis using RNA-seq and RT-PCR revealed that genes involved in cation exchange, auxin signaling, cell-wall modification, and transcription were differentially expressed between the OX and WT lines. Notably, salt overly sensitive 1, which is a sodium transporter, was highly upregulated in the OX lines. These results suggest that OsEXPA7 plays an important role in increasing salt stress tolerance by coordinating sodium transport, ROS scavenging, and cell-wall loosening.
Highlights
Salt stress is one of the most severe environmental stresses that cause plant growth retardation and significant crop loss
OsEXPA7 was cloned into pPZP vectors, which contain the promoter for CaMV 35S, phosphogluconate dehydrogenase (PGD), or OsEXPA7, the PinII terminator, and the selectable marker Bar (Figure 1A)
OsEXPA3 was shown to be induced in response to salt stress [39], and OsEXPA7 accumulated under cold stress [41]
Summary
Salt stress is one of the most severe environmental stresses that cause plant growth retardation and significant crop loss. Over-accumulation of ROS damages various cellular components and macromolecules, including the plasma membrane, nucleic acids, and proteins, which eventually leads to cell death [5]. To cope with this damage, plants induce the expression of genes associated with transcription factors, enzymes, and ion channels [6]. Na+ competes with K+ for being taken up through common transport systems since Na+ and K+ are physicochemically similar monovalent cations This leads to high Na+ and low K+ concentrations in the cytosol. Major tonoplast-localized sodium-hydrogen exchanger (NHX) proteins are essential for active K+
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