Genotype Differences In Response To Low Potassium Stress And The Mechanism Of Low Potassium Tolerance In Barley

Soil potassium deficiency has become a worldwide problem in agricultural production,seriously restricting crops productions and agricultural sustainable development.Therefore,revealing the physiological and molecular mechanisms of low potassium tolerance is quite important for breeding low potassium?LK?tolerance crop in order to alleviate the dependence on potash fertilizer.Tibetan annual wild barley?Hordeum vulgare L.subsp.spontaneum?is a unique and precious resource in China,and rich in genetic diversity,including abiotic stress tolerance.Identification of the genotypes with LK tolerance and the related genes can provide excellent genetic resources for breeding of LK tolerance in barley and other crops.In this study,Tibetan annual wild barley was used as main material to identify the physiological and molecular mechanisms of low potassium tolerance.The main results are as follows:1.Genotypic differences in growth and physiological characteristics of barley under LK stressTwo Tibetan wild barley genotypes differing in LK tolerance?XZ153,tolerant;XZ141,sensitive?and one barley cultivar ZD9?sensitive?,were treated with 0.01?low K treatment,LK?and 1?normal K treatment,NK?mM KCl for 15 d and 20 d at seeding stage.The results revealed that LK stress inhibited barley growth and induced a reduction of tissue dry weight,with XZ153 being less affected.Compared with the other two genotypes,XZ153 had less reduction in photosynthetic rate and SPAD value,and could translocate more K⁺from the older leaves to younger leaves under LK stress.Moreover,the activities of H⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase were increased significantly in all three genotypes under LK stress,and the highest H⁺/K⁺-ATPase activity was observed in XZ153.Thus the higher LK tolerance in XZ153 is mainly attributed to its stronger K⁺transfer ability,so that the younger leaves could maintain a relatively normal photosynthesis and metabolic activities.2.RNA-Seq based comparative transcriptome profiling analysis of barley leaves in responses to LK stressIn this study,Illumina RNA-Sequencing was performed using a Tibetan wild barley accession?XZ153,LK tolerance?and a barley cultivar?ZD9,LK sensitivity?to compare their transcriptome profiles of the different leaves in response to LK stress.A total of 7263 differentially expressed genes?DEGs?were detected in the topmost 2and 3 leaves?YL2,YL3?of the two genotypes under LK stress.In the term of DEGs number,XZ153 and YL2 had larger change than ZD9 and YL3,respectively.GO functional annotation analysis found that metabolic process,translation,RNA methylation and abscisic acid response were the major biological processes;The KEGG pathway enrichment analysis matched these DEGs encoded enzymes to 49KEGG pathways.It may be concluded that the LK tolerance of XZ153 is attributed to the following characteristics:stronger K⁺uptake and accumulation ability in YL2 of XZ153;relatively perfect SAM cycle and methionine pathway involving in ethylene biosynthesis.3.Identification of microRNAs and their targets in Tibetan wild and cultivated barleys in response to LK stressIn this study,the material used is the same as?2?,and small RNA and degradome analysis were performed to identify the miRNAs and theirs targets in the two barley genotypes responding to LK stress.Totally 1108 miRNAs were detected after LK stress,and their targets were also identified through bioinformatics prediction and degradome analysis.We identified 65 differentially expressed miRNAs responding to LK stress.Under LK stress,miR164c,miR169h and miR395a modules mediated TCA cycle,glycolysis pathway and pentose phosphate pathway responding;osa-miR166g-3p and ghr-miR482b may act as the regulators in Ca²⁺signaling pathway;the methionine salvage cycle involved in ethylene biosynthesis process mediated by miR396c-3p and osa-miR171e-5p might be another factors responding to LK stress;and miR160a,miR396c and miR169h modules might regulate plant photosynthesis,while these exclusively expressed miRNAs and their targets play the crucial roles in LK tolerance.4.Genome-wide association analysis of potassium uptake and translocation rates under low K stress in Tibetan wild barleyIn this study,we performed a genome-wide association analysis on 179 Tibetan wild barley accessions exposed to LK stress and investigated the associations of K⁺uptake rate?KUR?,K⁺translocation rate?KTR?and other K traits using 11,013diversity arrays technology markers.The results showed that there were significant differences in tissue K⁺concentration and content,KUR and KTR among the wild barley accessions.The measured values of all traits showed a normal distribution.Three significant quantitative trait loci?QTLs?for KUR and KTR were identified,located on 6H and 1H.These QTLs were found to be associated with the cation/H⁺antiporter,cyclic nucleotide gated channel and SAM-dependent methyltransferase.Moreover,some unique candidate genes associated with K-related signals were also identified,including K⁺channels,K⁺transporters and ethylene-related genes.