Academic literature on the topic 'OsHKT genes'

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.

Abstract This study was conducted with the target of determine the role of OsHKT4 and OsHKT6 genes in rice plants under salt stress and observe its gene expression by GUS technology, as well as studying the Na+ and K+ accumulation in different tissues. The results obtained show that OsHKT4::GUS appeared strong GUS activity, expressed mainly in vascular tissues. In contrast, the GUS activity of the OsHKT6 promoters in NaCl-treated leaves was greater than that in water-treated leaves. Also in wild type plants, increasing the Na+ concentration has the effect of increasing the Na+ content of the tissues generally, the old leaves accumulating more Na+ which reduced the K+ content in roots and old leaves (Na+ levels are higher in the leaf lower parts). These results suggest that OsHKT4 and OsHKT6 genes plays a role in the accumulation of Na+ in old leaves, by adopting the mechanical exclusion of toxic ions in the old leaves of the plant.

Methyl jasmonate (MeJA) is a potent player that fine-tunes growth and developmental activities under salinity stress. In this study, we investigated the influence of MeJA on two rice cultivars (NJ9108 and XD22) subjected to different salinity stresses. Following stress treatment, reduction in the water use efficiency, relative water contents, and membrane stability index in both cultivars were observed, whereas MeJA treatment partially alleviated the negative effects. MeJA treatment significantly increased the maximum photochemical efficiency (Fv/Fm) and electron transfer to photosystem II (Fv/Fo). Under salinity stress, MeJA treatment significantly triggered the H2O2 and APX accumulation, while POD and SOD remained unchanged in both cultivars. Salt stress increased Na+ concentration in the roots and leaves but decreased K+ concentration and the K+/Na+ ratio in both cultivars. However, MeJA-treated plants had the maximum K+ accumulation in both leaves and roots under saline conditions. The differential expression pattern of OsHKT and OsHAK genes implied that ion homeostasis is crucial to growth under salt stress. These findings suggest that the application of MeJA can be an alternative source of reducing salinity without compromising growth and yield.

Abstract A field experiment was carried out at the Agricultural Research and Experiments Station of the College of Agriculture, Al-Muthanna University during the summer season 2020. Pots of 15 cm diameter were used for planting the genotypes, with (SS, F-RCBD) and three replications. Ten different genotypes rice were used (FRI, FR2, FR15, FR16, FR17, FR18, FR21, FR25, FR27), as well as the rice varieties, which are Pokkali, Anber-33 and Jasmine, were irrigated by three levels of salty water (4.5, 7.5 and 15 ds/m). The results of the experiment showed that the tolerance of the genotypes FR21 and FR12 to salinity was associated with containing low concentrations of sodium (0.38 and 0.42%) respectively in the shoot, and a high concentration of potassium in the shoot (1.22 and 1.23%) respectively, and this result was reflected in the ratio of potassium to sodium in the shoot total was (3.30 and 2.95%) compared to the salt-tolerant variety Pokkali. Salinity caused a significant decrease in all the studied traits of the genotypes, especially at levels 7.5 and 15 ds/m, in growth traits (plant height, flag leaf area and panicle length), yield and its components (number of productive tillers, weight of 1000 grains and yield per plant). The most potent varieties in salt tolerance were FR12 and FR21, as they gave the highest yield of grains (11.72 and 16.67 g/plant, respectively), flag leave area (30.47 and 27.76 cm2 respectively). Detection for OsHKT4 and OsHKT6 by PCR proved the presence of primary locus that utilized by each gene with successfully fused genes as well as their stability under Iraqi cultivation circumstances, particularly in the case of FR12 and FR21 where OsHKT4 lanes were very obvious (2840 Kb) and the bands of OsHKT6 at (2324 Kb), which resemble to that in Pokkali Japanese salt tolerance rice. These results suggested the variation among investigated rice varieties in their tolerance to salts, where FR12 and FR21 were best in their performance under applied the salt levels conditions.

Potassium (K+), as a vital element, is involved in regulating important cellular processes such as enzyme activity, cell turgor, and nutrient movement in plant cells, which affects plant growth and production. Potassium channels are involved in the transport and release of potassium in plant cells. In the current study, three OsKAT genes and two OsAKT genes, along with 11 nonredundant putative potassium channel genes in the rice genome, were characterized based on their physiochemical properties, protein structure, evolution, duplication, in silico gene expression, and protein–protein interactions. In addition, the expression patterns of OsAKTs and OsKATs were studied in root and shoot tissues under salt stress using real-time PCR in three rice cultivars. K+ channel genes were found to have diverse functions and structures, and OsKATs showed high genetic divergence from other K+ channel genes. Furthermore, the Ka/Ks ratios of duplicated gene pairs from the K+ channel gene family in rice suggested that these genes underwent purifying selection. Among the studied K+ channel proteins, OsKAT1 and OsAKT1 were identified as proteins with high potential N-glycosylation and phosphorylation sites, and LEU, VAL, SER, PRO, HIS, GLY, LYS, TYR, CYC, and ARG amino acids were predicted as the binding residues in the ligand-binding sites of K+ channel proteins. Regarding the coexpression network and KEGG ontology results, several metabolic pathways, including sugar metabolism, purine metabolism, carbon metabolism, glycerophospholipid metabolism, monoterpenoid biosynthesis, and folate biosynthesis, were recognized in the coexpression network of K+ channel proteins. Based on the available RNA-seq data, the K+ channel genes showed differential expression levels in rice tissues in response to biotic and abiotic stresses. In addition, the real-time PCR results revealed that OsAKTs and OsKATs are induced by salt stress in root and shoot tissues of rice cultivars, and OsKAT1 was identified as a key gene involved in the rice response to salt stress. In the present study, we found that the repression of OsAKTs, OsKAT2, and OsKAT2 in roots was related to salinity tolerance in rice. Our findings provide valuable insights for further structural and functional assays of K+ channel genes in rice.

Soil salinity is a major problem in agriculture because high accumulation of Na+ ions in plants causes toxicity that can result in yield reduction. Na+/K+ homeostasis is known to be important for salt tolerance in plants. Na+/K+ homeostasis in rice (Oryza sativa L.) involves nine high-affinity K+ transporter (HKT) encoding Na+-K+ symporter, five OsNHX Na+/H+ antiporters, and OsSOS1 Na+/K+ antiporter genes. In the present study, we investigated various molecular and physiological processes to evaluate germination rate, growth pattern, ion content, and expression of OsHKT, OsNHX, and OsSOS1genes related to Na+/K+ homeostasis in different rice genotypes under salt stress. We found a significant increase in the germination percentage, plant vigor, Na+/K+ ratio, and gene expression of the OsHKT family in both the roots and shoots of the Nagdong cultivar and salt-tolerant cultivar Pokkali. In the roots of Cheongcheong and IR28 cultivars, Na+ ion concentrations were found to be higher than K+ ion concentrations. Similarly, high expression levels of OsHKT1, OsHKT3, and OsHKT6 were observed in Cheongcheong, whereas expression levels of OsHKT9 was high in IR28. The expression patterns of OsNHX and OsSOS1 and regulation of other micronutrients differed in the roots and shoots regions of rice and were generally increased by salt stress. The OsNHX family was also expressed at high levels in the roots of Nagdong and in the roots and shoots of Pokkali; in contrast, comparatively low expression levels were observed in the roots and shoots of Cheongcheong and IR28 (with the exception of high OsNHX1 expression in the roots of IR28). Furthermore, the OsSOS1 gene was highly expressed in the roots of Nagdong and shoots of Cheongcheong. We also observed that salt stress decreases chlorophyll content in IR28 and Pokkali but not in Cheongcheong and Nagdong. This study suggests that under salt stress, cultivar Nagdong has more salt-tolerance than cultivar Cheongcheong.

Abstract Background Saline land in coastal areas has great potential for crop cultivation. Improving salt tolerance in rice is a key to expanding the available area for its growth and thus improving global food security. Seed priming with salt (halopriming) can enhance plant growth and decrease saline intolerance under salt stress conditions during the subsequent seedling stage. However, there is little known about rice defense mechanisms against salinity at seedling stages after seed halopriming treatment. This study focused on the effect of seed halopriming treatment on salinity tolerance in a susceptible cultivar, IR 64, a resistant cultivar, Pokkali, and two pigmented rice cultivars, Merah Kalimantan Selatan (Merah Kalsel) and Cempo Ireng Pendek (CI Pendek). We grew these cultivars in hydroponic culture, with and without halopriming at the seed stage, under either non-salt or salt stress conditions during the seedling stage. Results The SES scoring assessment showed that the level of salinity tolerance in susceptible cultivar, IR 64, and moderate cultivar, Merah Kalsel, improved after seed halopriming treatment. Furthermore, seed halopriming improved the growth performance of IR 64 and Merah Kalsel rice seedlings. Quantitative PCR revealed that seed halopriming induced expression of the OsNHX1 and OsHKT1 genes in susceptible rice cultivar, IR 64 and Merah Kalsel thereby increasing the level of resistance to salinity. The expression levels of OsSOS1 and OsHKT1 genes in resistant cultivar, Pokkali, also increased but there was no affect on the level of salinity tolerance. On the contrary, seed halopriming decreased the expression level of OsSOS1 genes in pigmented rice cultivar, CI Pendek, but did not affect the level of salinity tolerance. The transporter gene expression induction significantly improved salinity tolerance in salinity-susceptible rice, IR 64, and moderately tolerant rice cultivar, Merah Kalsel. Induction of expression of the OsNHX1 and OsHKT1 genes in susceptible rice, IR 64, after halopriming seed treatment balances the osmotic pressure and prevents the accumulation of toxic concentrations of Na+, resulting in tolerance to salinity stress. Conclusion These results suggest that seed halopriming can improve salinity tolerance of salinity-susceptible and moderately tolerant rice cultivars.

Salinity is a major abiotic stress influencing agricultural production in Australia and around the world. Plants grown in saline conditions are affected by both osmotic and ionic stress components. The focus of this thesis is on the ionic stress component of salinity stress and in particular the build up of sodium ions (Na⁺) in the leaf cytoplasm, one of the main components of salinity toxicity. In this thesis, genes encoding the high affinity potassium transporter family of proteins (HKTs) are studied in the plants Oryza sativa (rice) and Arabidopsis thaliana (Arabidopsis). These HKT transporters encode Na⁺ permeable membrane proteins and transport either Na⁺ selectively or co-transport Na⁺ and K⁺. HKT transporters have been identified in a number of plant species and to date have mainly been shown to be involved in reducing Na⁺ stress. A family of nine HKT genes have been identified in rice. Published reports to date have mainly investigated the function of these OsHKT genes in heterologous systems or have focused on one or two OsHKT genes in planta. During this PhD, tissue specific expression profiles were determined for each of the nine OsHKT genes, in ten rice varieties, exposed to a NaCl stress. Of most interest was OsHKT1;3 which showed very high levels of expression in leaf blades and sheath and higher levels of expression in NaCl treated roots compared to controls, across rice varieties. A range of experiments were designed to obtain further information regarding OsHKT1;3, as little was known about this gene or the encoded protein at the time of these experiments. A notable discovery was the identification of a novel OsHKT1;3 splice variant. In contrast to rice, Arabidopsis has only one HKT gene, AtHKT1;1. AtHKT1;1 is located in cells surrounding the xylem and is likely to be involved in the retrieval of Na⁺ from the xylem, thereby minimising shoot Na⁺ accumulation. To investigate the regulation of AtHKT1;1 gene expression two Arabidopsis ecotypes, Columbia-0 (Col-0) and C24, shown by QRT-PCR to have different AtHKT1;1 root expression levels, were studied. Sequencing of the C24 AtHKT1;1 promoter revealed substantial sequence differences between the Col-0 and C24 promoters, particularly 150 to 200 bp upstream of the AtHKT1;1 ATG start codon. It was hypothesised that these sequence differences were responsible for the lack of AtHKT1;1 root specific expression in C24 plants, due to a lack of transcription factor binding motif(s) or particular root specific transcription factor(s). To test this hypothesis a series of AtHKT1;1 promoter::GFP and AtHKT1;1 promoter::AtHKT1;1 cDNA constructs, with different combinations of Col-0 and C24 sequences, were tested. Preliminary results suggest that both the Col-0 and C24 AtHKT1;1 promoters are able to drive expression of the downstream transgene and therefore the sequence differences between the promoters is not the cause of the lack of C24 AtHKT1;1 root expression. A 1.6 kb insertion, identified in the second intron of the C24 AtHKT1;1 gene, is now proposed to disrupt C24 AtHKT1;1 root specific expression.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2011