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

Nancy Ruiz-Lau,Emanuel Bojórquez-Quintal,María De Fátima Medina-Lara,Lucila A Sánchez-Cach,Manuel Martínez-Estévez,Begoña Benito,Ileana Echevarría-Machado

doi:10.3389/fpls.2016.01980

Abstract

High-affinity K+ (HAK) transporters are encoded by a large family of genes and are ubiquitous in the plant kingdom. These HAK-type transporters participate in low- and high-affinity potassium (K+) uptake and are crucial for the maintenance of K+ homeostasis under hostile conditions. In this study, the full-length cDNA of CcHAK1 gene was isolated from roots of the habanero pepper (Capsicum chinense). CcHAK1 expression was positively regulated by K+ starvation in roots and was not inhibited in the presence of NaCl. Phylogenetic analysis placed the CcHAK1 transporter in group I of the HAK K+ transporters, showing that it is closely related to Capsicum annuum CaHAK1 and Solanum lycopersicum LeHAK5. Characterization of the protein in a yeast mutant deficient in high-affinity K+ uptake (WΔ3) suggested that CcHAK1 function is associated with high-affinity K+ uptake, with Km and Vmax for Rb of 50 μM and 0.52 nmol mg−1 min−1, respectively. K+ uptake in yeast expressing the CcHAK1 transporter was inhibited by millimolar concentrations of the cations ammonium () and cesium (Cs+) but not by sodium (Na+). The results presented in this study suggest that the CcHAK1 transporter may contribute to the maintenance of K+ homeostasis in root cells in C. chinense plants undergoing K+-deficiency and salt stress.

Highlights

Plants require a variety of mineral nutrients throughout their ontogeny to complete their growth and development (Marschner, 2012)
Total RNA was isolated from the roots of C. chinense seedlings exposed to K+ starvation for 15 days to identify putative K+ transporters that can be expressed in this growth conditions
The cDNA corresponding to the CcHAK1 gene (KT202302) was isolated from the RNA of habanero pepper roots (C. chinense) grown in the absence of K+

Summary

Introduction

Plants require a variety of mineral nutrients throughout their ontogeny to complete their growth and development (Marschner, 2012). Potassium (K+) is one of the most important essential macronutrients and the most abundant inorganic cation in plant cells. Despite the abundance of K+ in the earth’s crust (2.1%), its low availability in the soil limits vegetal growth and reduces the productivity of large areas of arable land (Benito et al, 2014; Zörb et al, 2014). K+ fertilization has become a common and necessary practice in agriculture. Such fertilization is very expensive, and a great proportion of the added K+ is lost by lixiviation (Römheld and Kirkby, 2010; Zörb et al, 2014)

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