Characterization and Expression of KT/HAK/KUP Transporter Family Genes in Willow under Potassium Deficiency, Drought, and Salt Stresses.

Meixia Liang,Xiaoyan Zhang,Shaoying Zhang,Tingting Mao,Yachao Gao,Hongxia Zhang,Zhizhong Song

doi:10.1155/2020/2690760

Abstract

The K+ transporter/high-affinity K+/K+ uptake (KT/HAK/KUP) transporters dominate K+ uptake, transport, and allocation that play a pivotal role in mineral homeostasis and plant adaptation to adverse abiotic stresses. However, molecular mechanisms towards K+ nutrition in forest trees are extremely rare, especially in willow. In this study, we identified 22 KT/HAK/KUP transporter genes in purple osier willow (designated as SpuHAK1 to SpuHAK22) and examined their expression under K+ deficiency, drought, and salt stress conditions. Both transcriptomic and quantitative real-time PCR (qRT-PCR) analyses demonstrated that SpuHAKs were predominantly expressed in stems, and the expression levels of SpuHAK1, SpuHAK2, SpuHAK3, SpuHAK7, and SpuHAK8 were higher at the whole plant level, whereas SpuHAK9, SpuHAK11, SpuHAK20, and SpuHAK22 were hardly detected in tested tissues. In addition, both K+ deficiency and salt stress decreased the tissue K+ content, while drought increased the tissue K+ content in purple osier plant. Moreover, SpuHAK genes were differentially responsive to K+ deficiency, drought, and salt stresses in roots. K+ deficiency and salt stress mainly enhanced the expression level of responsive SpuHAK genes. Fifteen putative cis-acting regulatory elements, including the stress response, hormone response, circadian regulation, and nutrition and development, were identified in the promoter region of SpuHAK genes. Our findings provide a foundation for further functional characterization of KT/HAK/KUP transporters in forest trees and may be useful for breeding willow rootstocks that utilize potassium more efficiently.

Highlights

As one of the most abundant cations in plant cells, potassium (K+) is involved in many physiological and metabolic processes, such as stomatal movement, photosynthesis, respiration, cellular osmoregulation, and enzyme activation [1,2,3]
By BLAST searching of the Phytozome Genomics Resources, 22 putative strawberry SpuHAK genes were identified, which were entitled as SpuHAK1 to SpuHAK22
Except SpuHAK14 and 16 which are still unclear, all the other SpuHAK genes were distributed on 9 distinct chromosomes, in which 6 genes on the 3rd chromosome and 5 genes on the 1st chromosome

Summary

Introduction

As one of the most abundant cations in plant cells, potassium (K+) is involved in many physiological and metabolic processes, such as stomatal movement, photosynthesis, respiration, cellular osmoregulation, and enzyme activation [1,2,3]. Application of K+ fertilizer favorably improved leaf growth [4, 5], flowering [6], wood quality, and yield [7,8,9]. Plants need to uptake an optimal amount of K+ via highaffinity K+ transporter uptake system in roots from the soil, to maintain normal growth [3, 11, 12]. K+ transporters can be divided into four families: KT/HAK/KUP, Trk/HKT, CHX, and KEA [1, 13], which play an important role in improving plant tolerance to different abiotic stresses such as drought [14,15,16], salt [17,18,19,20,21], and heavy metal stresses [22, 23]. KT/HAK/KUP transporters are one of the largest K+ transporter families, which function in acquiring K+, catalyzing K+ uptake across a wide range of external

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Conclusion