期刊
ANNALS OF BOTANY
卷 115, 期 3, 页码 495-507出版社
OXFORD UNIV PRESS
DOI: 10.1093/aob/mcu177
关键词
Xerohalophyte; tonoplast Na+/H+ antiporter ZxNHX; Na+ and K+ homeostasis; long-distance transport; gene silencing; ZxSOS1; ZxHKT1; 1, Zygophyllum xanthoxylum
资金
- National Basic Research Program of China (973 Program) [2014CB138701]
- National Natural Science Foundation of China [31170431]
- Specialized Research Fund for the Doctoral Program of Higher Education of China [20130211130001]
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 ZacSOS/ but only an 80 % increase in transcripts of ZacHKT1; 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 ANHX-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 ZacSOS/ by only 10 %, whereas transcripts of ZacHKT1;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 ANHX also triggered a downregulation of ZxAKT1 and ASKOR in roots, resulting in a significant decrease in K+ accumulation in all the tissues in plants grown in 50 mmNaCl. These changes led to a significant reduction in osmotic adjustment, and thus an inhibition of growth in ANHX-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.
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