Transcriptome-Wide Analysis Revealed the Potential of the High-Affinity Potassium Transporter (HKT) Gene Family in Rice Salinity Tolerance via Ion Homeostasis

Abstract

The high-affinity potassium transporter (HKT) genes are key ions transporters, regulating the plant response to salt stress via sodium (Na⁺) and potassium (K⁺) homeostasis. The main goal of this research was to find and understand the HKT genes in rice and their potential biological activities in response to brassinosteroids (BRs), jasmonic acid (JA), seawater, and NaCl stress. The in silico analyses of seven OsHKT genes involved their evolutionary tree, gene structures, conserved motifs, and chemical properties, highlighting the key aspects of OsHKT genes. The Gene Ontology (GO) analysis of HKT genes revealed their roles in growth and stress responses. Promoter analysis showed that the majority of the HKT genes participate in abiotic stress responses. Tissue-specific expression analysis showed higher transcriptional activity of OsHKT genes in roots and leaves. Under NaCl, BR, and JA application, OsHKT1 was expressed differentially in roots and shoots. Similarly, the induced expression pattern of OsHKT1 was recorded in the seawater resistant (SWR) cultivar. Additionally, the Na⁺ to K⁺ ratio under different concentrations of NaCl stress has been evaluated. Our data highlighted the important role of the OsHKT gene family in regulating the JA and BR mediated rice salinity tolerance and could be useful for rice future breeding programs.

Keywords: HKT; hormones; rice; salinity; seawater.

Figure 1

HKT protein phylogeny in three plants: T. aestivum, Zea maize, and O. sativa. MEGA 7 was used for the phylogenetic tree using the following parameters: Bootstrap D 1000 replicates, maximum likelihood method, and Poisson correction. All group members were divided into five groups, each represented by an assorted color. Different labels were used to identify members of various species.

Figure 2

Conserved motifs analysis of OsHKT genes in rice. The motif locations and logo are presented separately. The sequences of 5 conserved motifs are presented in the box called Motif Consensus.

Figure 3

Gene structure analysis of OsHKT genes in rice. The red bars show CDS regions, whereas the grey lines represent introns. The blue bars at both ends display upstream/downstream regions.

Figure 4

Gene ontology of the OsHKT gene family in rice. The figure displays the predicted biological, molecular, and cellular functions of OsHKT genes.

Figure 5

Cis-acting elements presented in the 1.5 kb upstream regions of OsHKT genes. The figure shows hormonal, stress, and growth responsive cis-regulatory elements of the OsHKT gene family in rice.

Figure 6

Predictive protein interaction analysis of OsHKT1 genes in rice. Our reference protein is in the middle in red.

Figure 7

Tissue-specific expression analysis of the OsHKT gene family in rice. Data were obtained from a publicly available database. Rows represent OsHKT members, and columns show different developmental stages and tissues. The expression level of OsHKT [log2 (FPKM  +  1)] is shown by the intensity of color; red represents high expression and blue represents low expression.

Figure 8

Expression analysis of the OsHKT gene family in rice roots under brassinosteroids application. Rows represent OsHKT members, and columns show different time points. The expression level of OsHKT [log2 (FPKM + 1)] is shown by the intensity of color: red represents high expression, and blue represents low expression.

Figure 9

Expression analysis of OsHKT genes in rice roots under Jasmonic acid application. Rows represent OsHKT members, and columns show different time points. The expression level of OsHKT [log2 (FPKM  +  1)] is indicated by the intensity of color: red represents high expression and blue represents low expression.

Figure 10

Expression analysis of the OsHKT gene family in rice roots and stems under saline conditions. Different treatments were represented with different colors. ANOVA was used to test significance. p  <  0.05. Error bars represent standard deviation.

Figure 11

Expression analysis of the OsHKT gene family in the salinity resistant cultivar subjected to sea water stress. Control (CK) and seawater resistant (SWR). Different treatments are represented with different colors. ANOVA was used to test significance at p < 0.05 probability level. Error bars represent standard deviation.

Figure 12

Na⁺, K⁺, and ratio in tolerant cultivar (3Y9H) and five salt concentration treatments (0, 25, 50, 75, and 100 mM). Different letters showed the significant variance at p < 0.05.

Figure 13

Na⁺, K⁺, and ratio in sensitive cultivar (JLY252) and five salt concentration treatments (0, 25, 50, 75, and 100 mM). Different letters showed the significant variance at p < 0.05.