The Function Of Wheat Potassium Transporter Gene TaHAK11 In Lateral Root Formation

Potassium is the most abundant mineral nutrient in plants,accounting for 2%to 10%of the dry weight of plants.Potassium is a major inorganic substance participating in plant leaf growth,stomatal opening,axial growth and tropism.Potassium also serves as an important signaling factor that mediates the adaptive response of plants to the environment.With the increase of the intensification of grain cultivation and the wide planting of high-yield varieties,potassium consumption of potassium in farmland soils is rising,resulting in a decline in wheat yield and quality deterioration.In recent years,the phenomenon of potassium deficiency has become more and more serious in China,which seriously affects food security.Our group previously bred a wheat introgression cultivar Shanrong No.3(SR3)via asymmetric somatic cell hybridization approach with the common wheat Jinan 177 and wheatgrass as parents.Based on transcriptomic analysis,a KT/KUP/HAK transporter family cluster III gene TaHAKll was identified.TaHAK11 was responsive to abiotic stress and showed differential expression between SR3 and JN177.TaHAK11 had two copies,TaHAK11-3 and its paralog TaHAK11-5,whose peptide sequences had allelic difference at five amino acid resides.Previous studies found that TaHAK11-3 and TaHAK11-5 were highly expressed in the lateral root primordia;their overexpression promoted lateral root formation in Arabidopsis,and the promotion was erased when potassium influx was inhibited.In this work,we found:1.In comparison with the wildtype,TaHAK11-3 and TaHAK11-5 overexpressing lines accumulated more potassium in root and lateral root primordia.After exposure to potassium influx inhibitor,the increase of lateral root primordia was eliminated.The result indicates that the promotion of TaHAKll to lateral root formation is achieved via elevating potassium influx to increase the potassium content in roots,especially in lateral root primordia.2.TaHAK11-3 and TaHAK11-5 overexpression increased the expression of auxin transporters PIN 1 and PIN2 as well as auxin responsive genes such as ARF7 and ARF19,and promoted the fluorescence signals of PIN1/2-GFP at lateral root primordia,indicating that TaHAK11 promotes the transporting of auxin to lateral root primordia,and enlarges auxin signaling pathway.The inhibitor of potassium influx erased the promotion of TaHAKll overexpression to PIN1/2-GFP signal accumulation at lateral root primordia and the expression of genes involved in auxin signaling pathway,showing that TaHAK11 promotes auxin transporting and response via elevating potassium influx.TaHAK11 did not physically interact with PIN1/2,primarily demonstrating that potassium influx does not couple with auxin transmembrane-transporting,but leads to increase in intracellular potassium content and therefore promotes auxin transporting and lateral root formation.3.Auxin induced the expression of TaHAK11-3 and TaHAK11-5 in roots,and ARF7 was found to bind the promoters of TaHAK11-3 and TaHAK11-5.The result indicates that auxin may modulate the expression of TaHAK11-3 and TaHAK11-5 via ARP7,and the induction of TaHAKll-3 and TaHAKll-5 in turn enhances auxin transporting,which forms a positive feedback loop to promote lateral root formation.