Genome-Wide Identification of the <i>Gossypium hirsutum</i> NHX Genes Reveals that the Endosomal-Type <i>GhNHX4A</i> is Critical for the Salt Tolerance of Cotton

• Main Authors: Wenyu Ma, Zhongying Ren, Yang Zhou, Junjie Zhao, Fei Zhang, Junping Feng, Wei Liu, Xiongfeng Ma
• Format: Article
• Language: English
• Published: MDPI AG 2020-10-01
• Series: International Journal of Molecular Sciences
• Subjects: <i>Gossypium hirsutum</i>; salt stress; Na⁺/H⁺ antiporter; genome-wide identification; virus-induced gene silencing
• Online Access: https://www.mdpi.com/1422-0067/21/20/7712

Soil salinization, which is primarily due to excessive Na⁺ levels, is a major abiotic stress adversely affecting plant growth and development. The Na⁺/H⁺ antiporter (NHX) is a transmembrane protein mediating the transport of Na⁺ or K⁺ and H⁺ across the membrane to modulate the ionic balance of plants in response to salt stress. Research regarding NHXs has mainly focused on the vacuolar-type NHX family members. However, the biological functions of the endosomal-type NHXs remain relatively uncharacterized. In this study, 22 NHX family members were identified in <i>Gossypium hirsutum</i>. A phylogenetic analysis divided the <i>GhNHX</i> genes into two categories, with 18 and 4 in the vacuolar and endosomal groups, respectively. The chromosomal distribution of the NHX genes revealed the significant impact of genome-wide duplication during the polyploidization process on the number of <i>GhNHX</i> genes. Analyses of gene structures and conserved motifs indicated that <i>GhNHX </i>genes in the same phylogenetic cluster are conserved. Additionally, the salt-induced expression patterns confirmed that the expression levels of most of the <i>GhNHX</i> genes are affected by salinity. Specifically, in the endosomal group, <i>GhNHX4A</i> expression was substantially up-regulated by salt stress. A yeast functional complementation test proved that <i>GhNHX4A</i> can partially restore the salt tolerance of the salt-sensitive yeast mutant AXT3. Silencing <i>GhNHX4A</i> expression decreased the resistance of cotton to salt stress because of an increase in the accumulation of Na⁺ in stems and a decrease in the accumulation of K⁺ in roots. The results of this study may provide the basis for an in-depth characterization of the regulatory functions of NHX genes related to cotton salt tolerance, especially the endosomal-type <i>GhNHX4A</i>. Furthermore, the presented data may be useful for selecting appropriate candidate genes for the breeding of new salt-tolerant cotton varieties.