Abstract
Soil salinity is a main abiotic stress in agriculture worldwide. The Na+/H+ antiporters (NHXs) play pivotal roles in intracellular Na+ excretion and vacuolar Na+ compartmentalization, which are important for plant salt stress resistance (SSR). However, few systematic analyses of NHXs has been reported in allotetraploid rapeseed so far. Here, a total of 18 full-length NHX homologs, representing seven subgroups (NHX1-NHX8 without NHX5), were identified in the rapeseed genome (AnAnCnCn). Number variations of BnaNHXs might indicate their significantly differential roles in the regulation of rapeseed SSR. BnaNHXs were phylogenetically divided into three evolutionary clades, and the members in the same subgroups had similar physiochemical characteristics, gene/protein structures, and conserved Na+ transport motifs. Darwin´s evolutionary pressure analysis suggested that BnaNHXs suffered from strong purifying selection. The cis-element analysis revealed the differential transcriptional regulation of NHXs between the model Arabidopsis and B. napus. Differential expression of BnaNHXs under salt stress, different nitrogen forms (ammonium and nitrate), and low phosphate indicated their potential involvement in the regulation of rapeseed SSR. Global landscapes of BnaNHXs will give an integrated understanding of their family evolution and molecular features, which will provide elite gene resources for the genetic improvement of plant SSR through regulating the NHX-mediated Na+ transport.
Highlights
Plants are usually exposed to various environmental stresses, among which salinity is one of the major limiting factors for plant growth and development, and crop productivity [1,2,3]
Arabidopsis NHXs can be divided into three main groups: (i) AtNHX1-4 localized on the tonoplast, (ii) AtNHX5-6 localized on the endosomal compartment, and (iii) AtSOS1 (Salt Overly Sensitive 1)/NHX7 and AtNHX8 localized on the plasma membrane [9,10,11]
To identify the NHX family members in diverse plant species, we used the amino acid sequences of Arabidopsis NHXs as queries to perform BLASTp search against the genome databases of B. rapa (‘Chiifu-401’), B. oleracea (‘TO1000’), B. napus (‘Darmor-bzh’), and other plant species
Summary
Plants are usually exposed to various environmental stresses, among which salinity is one of the major limiting factors for plant growth and development, and crop productivity [1,2,3]. Plants have developed multiple strategies to cope with salt stresses, including the regulation of growth and development, ion homeostasis, detoxification and osmotic adjustment [5]. The maintenance of ion homeostasis plays an essential role in the plant salt stress resistance (SSR). The decrease in sodium ion (Na+) concentrations and the increase in potassium ion (K+) concentrations, leading to a high K+/Na+ ratio, are very crucial for plant SSR. In this process, the Na+/H+ antiporters (NHXs) are very important players. The silencing of GhNHX1 resulted in the enhanced sensitivity of cotton seedlings to high salt concentrations, which suggested that GhNHX1 positively regulated the cotton resistance to salt stress [24]. Ectopic expression of Arabidopsis NHX5 enhanced the soybean SSR [26]
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