Overexpression of Iris lactea tonoplast Na⁺/H⁺ antiporter gene IlNHX confers improved salt tolerance in tobacco

Abstract

Sodium cation compartmentalization into vacuoles is one of the effective strategies for adaptation of halophytes to saline environments. Tonoplast Na + /H + antiporter (NHX) is involved in Na + sequestration into vacuoles under salt stress. However, the function of NHX in halophyte Iris lactea is still unclear. In this study, a significant positive correlation was observed between Na + accumulations and IlNHX expression in tissues under 0-200 mM NaCl, indicating IlNHX might be responsible for Na + accumulation of I. lactea under salt stress. More important, IlNHX was specifically localized to the tonoplast. Transgenic tobacco expressing IlNHX grew better and showed higher tolerance to 200 mM NaCl than respective wild type (WT). Compared to WT, transgenic tobacco accumulated more Na + and K + and maintained higher K + /Na + ratios in tissues, accompanied by the reduction of chlorophyll loss and lipid peroxidation in the presence of NaCl. Moreover, transgenic tobacco exhibited markedly higher vacuolar H +-ATPase (V-ATPase) activity relative to WT when subjected to salt stress. The findings suggest that transgenic plants overexpressing IlNHX could compartmentalize more Na + into vacuoles in tobacco via enhanced V-ATPase activity, which further contributes to maintaining K + and Na + homeostasis, to improved photosynthesis, and to protection of cell membrane integrity under salt stress.

Root vacuolar sequestration and suberization contribute to salinity tolerance in Pistacia spp. rootstocks

“…Thus, additional mechanisms must be employed to limit salt transport to the salinity sensitive leaves. Vacuolar sequestration of Na + is one such mechanism that reduces the amount of salt reaching the shoot, therefore reducing salt toxicity (Zhang and Blumwald, 2001;Gonzalez et al, 2012;Gupta and Huang, 2014;Guo et al, 2020). The dominant role of vacuolar Na + sequestration over Na + exclusion in salinity tolerance was recently demonstrated in barley.…”

“…UCB1 plants showed a higher vacuolar Na + sequestration capacity compared to P. integerrima (Fig 3). It is likely that UCB1 is more efficient at vacuolar sequestration due to the increased activity of salt ion antiporters such as the NHX transporter family (Gupta and Huang, 2014;Bassil et al, 2019;Guo et al, 2020). Overexpression of NHX1 increases salt tolerance in diverse species such as wheat, rice, tomato and mung bean (Zhang and Blumwald, 2001;Moghaieb et al, 2014;Kumar et al, 2017;Zeng et al, 2018) and likely contributes to vacuolar sequestration in pistachio.…”

“…Plants can maximize intracellular compartmentalization of salt in tissues by sequestering excessive salt ions within vacuoles to reduce cytosolic toxicity (Zhang and Blumwald, 2001;Gonzalez et al, 2012;Gupta and Huang, 2014;Munns et al, 2016;Guo et al, 2020). This process is mediated by the H + /Na + antiporters, encoded by the NHX1/2 genes (Zhang and Blumwald, 2001;Bassil et al, 2019).…”

Root vacuolar sequestration and suberization are prominent responses of Pistacia spp. rootstocks during salinity stress

“…Overexpression of NHX1 , a salt ion antiporter, increases salt tolerance in diverse species such as wheat, rice, tomato, and mung bean (Kumar et al., 2017; Moghaieb et al., 2014; Zeng et al., 2018; Zhang & Blumwald, 2001). UCB1 may exhibit higher salinity tolerance compared to P. integerrima due to an increased efficiency at vacuolar sequestration via increased expression or activity of salt ion antiporters such as the NHX1 (Bassil et al., 2019; Guo et al., 2020; Gupta & Huang, 2014). Retention of Na + in the vacuole can also be affected by the back‐leak of Na + into the cytosol via cation channels or tonoplast permeability (Isayenkov et al., 2010; Leach et al., 1990; Munns et al., 2016, 2020).…”

“…Molecular mechanisms include the Salt Overly Sensitive (SOS) pathway at the plasma membrane, which regulates sodium ion (Na + ) efflux from the cytosol (Lin et al., 2009; Shi et al., 2000, 2003; Tester & Davenport, 2003; Yang et al., 2009; Zhu, 2002), and HKT1‐type transporters, which contribute to reducing root to shoot Na + transport by retrieving Na + from the xylem (Davenport et al., 2007; Hauser & Horie, 2010; Møller et al., 2009; Rubio et al., 1995). Furthermore, intracellular compartmentalization of salt ions via vacuolar sequestration to reduce cytosolic toxicity is mediated by H + /Na + antiporters, encoded by the NHX1/2 genes (Bassil et al., 2019; Gonzalez et al., 2012; Guo et al., 2020; Gupta & Huang, 2014; Munns et al., 2016; Zhang & Blumwald, 2001). Such pathways are being explored to obtain salinity tolerance in different crop and non‐crop species (Escalante‐Pérez et al., 2009; Henderson et al., 2018; Shohan et al., 2019; Yang et al., 2009; Zhang et al., 2019).…”