Hui-Jun Yuan1, Qing Ma1, Guo-Qiang Wu2, Pei Wang1, Jing Hu1, Suo-Min Wang3. 1. State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou 730020, PR China. 2. School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, PR China. 3. State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou 730020, PR China smwang@lzu.edu.cn.
Abstract
BACKGROUND AND AIMS: In order to cope with arid environments, the xerohalophyte Zygophyllum xanthoxylum efficiently compartmentalizes Na(+) into vacuoles, mediated by ZxNHX, and maintains stability of K(+) in its leaves. However, the function of ZxNHX in controlling Na(+) and K(+) homeostasis at the whole-plant level remains unclear. In this study, the role of ZxNHX in regulating the expression of genes involved in Na(+) and K(+) transport and spatial distribution was investigated. METHODS: The role of ZxNHX in maintaining Na(+) and K(+) homeostasis in Z. xanthoxylum was studied using post-transcriptional gene silencing via Agrobacterium-mediated transformation. Transformed plants were grown with or without 50 mm NaCl, and expression levels and physiological parameters were measured. KEY RESULTS: It was found that 50 mm NaCl induced a 620 % increase in transcripts of ZxSOS1 but only an 80 % increase in transcripts of ZxHKT1;1 in roots of wild-type (WT) plants. Consequently, the ability of ZxSOS1 to transport Na(+) exceeded that of ZxHKT1;1, and Na(+) was loaded into the xylem by ZxSOS1 and delivered to the shoots. However, in a ZxNHX-silenced line (L7), the capacity to sequester Na(+) into vacuoles of leaves was weakened, which in turn regulated long-distance Na(+) transport from roots to shoots. In roots of L7, NaCl (50 mm) increased transcripts of ZxSOS1 by only 10 %, whereas transcripts of ZxHKT1;1 increased by 53 %. Thus, in L7, the transport ability of ZxHKT1;1 for Na(+) outweighed that of ZxSOS1. Na(+) was unloaded from the xylem stream, consequently reducing Na(+) accumulation and relative distribution in leaves, but increasing the relative distribution of Na(+) in roots and the net selective transport capacity for K(+) over Na(+) from roots to shoots compared with the WT. Silencing of ZxNHX also triggered a downregulation of ZxAKT1 and ZxSKOR in roots, resulting in a significant decrease in K(+) accumulation in all the tissues in plants grown in 50 mm NaCl. These changes led to a significant reduction in osmotic adjustment, and thus an inhibition of growth in ZxNHX-silenced lines. CONCLUSIONS: The results suggest that ZxNHX is essential for controlling Na(+), K(+) uptake, long-distance transport and their homeostasis at whole-plant level via feedback regulation of the expression of genes involved in Na(+), K(+) transport. The net result is the maintenance of the characteristic salt accumulation observed in Z. xanthoxylum and the regulation of its normal growth. A model is proposed for the role of ZxNHX in regulating the Na(+) transport system in Z. xanthoxylum under saline conditions.
BACKGROUND AND AIMS: In order to cope with arid environments, the xerohalophyte Zygophyllum xanthoxylum efficiently compartmentalizes Na(+) into vacuoles, mediated by ZxNHX, and maintains stability of K(+) in its leaves. However, the function of ZxNHX in controlling Na(+) and K(+) homeostasis at the whole-plant level remains unclear. In this study, the role of ZxNHX in regulating the expression of genes involved in Na(+) and K(+) transport and spatial distribution was investigated. METHODS: The role of ZxNHX in maintaining Na(+) and K(+) homeostasis in Z. xanthoxylum was studied using post-transcriptional gene silencing via Agrobacterium-mediated transformation. Transformed plants were grown with or without 50 mm NaCl, and expression levels and physiological parameters were measured. KEY RESULTS: It was found that 50 mm NaCl induced a 620 % increase in transcripts of ZxSOS1 but only an 80 % increase in transcripts of ZxHKT1;1 in roots of wild-type (WT) plants. Consequently, the ability of ZxSOS1 to transport Na(+) exceeded that of ZxHKT1;1, and Na(+) was loaded into the xylem by ZxSOS1 and delivered to the shoots. However, in a ZxNHX-silenced line (L7), the capacity to sequester Na(+) into vacuoles of leaves was weakened, which in turn regulated long-distance Na(+) transport from roots to shoots. In roots of L7, NaCl (50 mm) increased transcripts of ZxSOS1 by only 10 %, whereas transcripts of ZxHKT1;1 increased by 53 %. Thus, in L7, the transport ability of ZxHKT1;1 for Na(+) outweighed that of ZxSOS1. Na(+) was unloaded from the xylem stream, consequently reducing Na(+) accumulation and relative distribution in leaves, but increasing the relative distribution of Na(+) in roots and the net selective transport capacity for K(+) over Na(+) from roots to shoots compared with the WT. Silencing of ZxNHX also triggered a downregulation of ZxAKT1 and ZxSKOR in roots, resulting in a significant decrease in K(+) accumulation in all the tissues in plants grown in 50 mm NaCl. These changes led to a significant reduction in osmotic adjustment, and thus an inhibition of growth in ZxNHX-silenced lines. CONCLUSIONS: The results suggest that ZxNHX is essential for controlling Na(+), K(+) uptake, long-distance transport and their homeostasis at whole-plant level via feedback regulation of the expression of genes involved in Na(+), K(+) transport. The net result is the maintenance of the characteristic salt accumulation observed in Z. xanthoxylum and the regulation of its normal growth. A model is proposed for the role of ZxNHX in regulating the Na(+) transport system in Z. xanthoxylum under saline conditions.
Authors: Raquel Olías; Zakia Eljakaoui; Jun Li; Paz Alvarez De Morales; Mari Carmen Marín-Manzano; Jose M Pardo; Andrés Belver Journal: Plant Cell Environ Date: 2009-03-03 Impact factor: 7.228
Authors: Zaida Andrés; Javier Pérez-Hormaeche; Eduardo O Leidi; Kathrin Schlücking; Leonie Steinhorst; Deirdre H McLachlan; Karin Schumacher; Alistair M Hetherington; Jörg Kudla; Beatriz Cubero; José M Pardo Journal: Proc Natl Acad Sci U S A Date: 2014-04-14 Impact factor: 11.205