The potassium transporter OsHAK21 functions in the maintenance of ion homeostasis and tolerance to salt stress in rice

Abstract

The intracellular potassium (K(+) ) homeostasis, which is crucial for plant survival in saline environments, is modulated by K(+) channels and transporters. Some members of the high-affinity K(+) transporter (HAK) family are believed to function in the regulation of plant salt tolerance, but the physiological mechanisms remain unclear. Here, we report a significant inducement of OsHAK21 expression by high-salinity treatment and provide genetic evidence of the involvement of OsHAK21 in rice salt tolerance. Disruption of OsHAK21 rendered plants sensitive to salt stress. Compared with the wild type, oshak21 accumulated less K(+) and considerably more Na(+) in both shoots and roots, and had a significantly lower K(+) net uptake rate but higher Na(+) uptake rate. Our analyses of subcellular localizations and expression patterns showed that OsHAK21 was localized in the plasma membrane and expressed in xylem parenchyma and individual endodermal cells (putative passage cells). Further functional characterizations of OsHAK21 in K(+) uptake-deficient yeast and Arabidopsis revealed that OsHAK21 possesses K(+) transporter activity. These results demonstrate that OsHAK21 may mediate K(+) absorption by the plasma membrane and play crucial roles in the maintenance of the Na(+) /K(+) homeostasis in rice under salt stress.

Molecular Cloning and Functional Analysis of a Na+-Insensitive K+ Transporter of Capsicum chinense Jacq

“…However, K + uptake through the PhaHAK2 and HvHAK1 transporters is sensitive to high concentrations of Na + (Takahashi et al, 2007a; Fulgenzi et al, 2008; Véry et al, 2014). In rice roots, hulls and vascular tissues, the levels of OsHAK5 and OsHAK21 transcripts are positively regulated by high concentrations of NaCl under conditions of low and high K + availability (Yang et al, 2014; Shen et al, 2015). …”

“…At the transcriptional level, the members of this family are expressed in different tissues and organs (Su et al, 2002; Ahn et al, 2004; Yang et al, 2014; Song Z. et al, 2015) and are regulated by physiological conditions and environmental factors in a differential manner according to the group to which they belong (Véry et al, 2014; Song Z. et al, 2015). In particular, the genes that encode the HAK transporters of group I are positively regulated in roots under K + starvation (Santa-María et al, 1997; Bañuelos et al, 2002; Ahn et al, 2004; Martínez-Cordero et al, 2004; Nieves-Cordones et al, 2007; Alemán et al, 2009; Horie et al, 2011; Shen et al, 2015), suggesting an adaptive role of group I transporters under conditions of low K + availability. The positive regulation of the HAK genes by K + deficiency can be inhibited by the presence of various ions.…”

“…The positive regulation of the HAK genes by K + deficiency can be inhibited by the presence of various ions. It has been reported that the cation sodium (Na + ) prevents positive regulation by K + starvation of LeHAK5, AtHAK5 , and ThHAK5 (Nieves-Cordones et al, 2007; Alemán et al, 2009), whereas the expression of HvHAK1, OsHAK5, OsHAK21 , and some members of group II such as McHAK1, McHAK3 , and PhaHAK2 increases under these conditions (Su et al, 2002; Takahashi et al, 2007a; Fulgenzi et al, 2008; Yang et al, 2014; Shen et al, 2015). Ammonium (${\text{NH}}_4^{+}$) and cesium (Cs + ) can induce the expression of HAK-type genes, suggesting the participation of HAK-type gene products in their transport and/or an effect of ${\text{NH}}_4^{+}$ and Cs + on K + levels through competitive inhibition (Nieves-Cordones et al, 2007; Qi et al, 2008; ten-Hoopen et al, 2010).…”

“…Recently, the participation of HAK transporters of group I in the maintenance of K + homeostasis under hostile conditions has been reported (Nieves-Cordones et al, 2010, 2014; Alemán et al, 2014; Chérel et al, 2014; Yang et al, 2014; Shen et al, 2015). Salinity can induce K + deficiency by inhibiting influx and increasing K + efflux in roots, resulting in decreased K + content of the plant (Bojórquez-Quintal et al, 2014; Demidchik, 2014; Shabala and Pottosin, 2014).…”

“…Its expression in the bright yellow 2 (BY2) tobacco cell line has demonstrated to increase the salinity tolerance of the cells (Horie et al, 2011), and overexpression of the same transporter in rice increased the K + /Na + ratio and salt stress tolerance, suggesting the maintenance of high-affinity K + uptake in the presence of Na + (Yang et al, 2014). Also, AtHAK5 and OsHAK21 plays an important role in the absorption of K + under conditions of K + deficiency and high levels of Na + (Nieves-Cordones et al, 2010; Shen et al, 2015). …”