Untitled

Abstract

Potassium is an essential macronutrient in higher plants. It plays an important physiological role in stoma movements, osmoregulation, enzyme activation and cell expansion. The demand for potassium can be substantial, especially when the plant concerned is a Eucalyptus tree in excess of 50 m tall. We have isolated two cDNAs, EcHKT1 and EcHKT2, from Eucalyptus camaldulensis (river red gum) which are expressed in leaves, stems and roots. These encode potassium transporter polypeptides with homology to the wheat K+-Na+ symporter, HKT1. EcHKT1 and EcHKT2 both complemented the K+-limited growth of an Escherichia coli K+-uptake-deficient triple mutant. EcHKT1 and EcHKT2 also mediated Na+ and K+ uptake when expressed in Xenopus oocytes. A comparison of the EcHKT1 and EcHKT2 sequences and their transport properties indicated that these cDNAs represent two K+ transporters with distinct functional characteristics. The functional and structural conservation between these two E. camaldulensis genes and the wheat HKT1 suggests that they play an important, albeit elusive, physiological role.

Glycine residues in potassium channel-like selectivity filters determine potassium selectivity in four-loop-per-subunit HKT transporters from plants

“…4). Surprisingly, EcHKT1 and EcHKT2 from eucalyptus transported K ϩ when expressed in Xenopus oocytes, although both proteins have a serine at the predicted filter position in P-loop A (21,23). However, mutations in rice OsHKTs (Fig.…”

“…HKT1 homologs were identified from Arabidopsis (20), eucalyptus (21), rice (22) (14,19,20). K ϩ ͞Na ϩ selectivity is of particular importance in plant nutrition.…”

All Four Putative Selectivity Filter Glycine Residues in KtrB Are Essential for High Affinity and Selective K+ Uptake by the KtrAB System from Vibrio alginolyticus

“…and yeast, several plant HKT proteins containing a serine residue instead of glycine in the first pore segment (P A ) transport Na ϩ rather than K ϩ (8,11,28,44,45). We wished to determine whether a similar phenomenon occurs for the VaKtrB serine variants.…”

Role of Na+, K+, Cl-, proline and sucrose concentrations in determining salinity tolerance and their correlation with the expression of multiple genes in tomato

“…For example, HKT (Berthomieu et al 2003; Ren et al 2005; Davenport et al 2007; Moller et al 2009; Jha et al 2010; Ali et al 2012), SOS (Qiu et al 2002; Shi et al 2002), NHX (Gaxiola et al 1999), AVP (Gaxiola et al 2001; Zhao et al 2006) and AHA (Apse et al 1999) gene families encompass such genes. Studies carried out with Arabidopsis (Uozumi et al 2000; Berthomieu et al 2003; Davenport et al 2007; Moller et al 2009), rice (Ren et al 2005; Jabnoune et al 2009; Yao et al 2010), Eucalyptus (Fairbairn et al 2000), barley (Mian et al 2011) and Thellungiella (Ali et al 2012) show that HKT genes are involved in the control of the Na + movement throughout the plant. The HKT gene family encodes proteins that are responsible for the influx of Na + into cells (Uozumi et al 2000; Moller et al 2009).…”