Genome Identification Of BvHAKs And BvHKTs And Analysis Of Their Expression Patterns In Sugar Beet Under Salt Treatment

K⁺is the most abundant inorganic cation in plants,and it is also a necessary nutrient element for plant growth and development.HAK（high affinity K⁺transporter）and HKT（high affinity K⁺transporter）are the largest K⁺transporters in plants.They play important roles in K⁺absorption and transport in plants.However,the expression and genome-wide analysis of HAK and HKT genes in sugar beet have not been reported,especially in response to salt stress under potassium deficiency.In this paper,sugar beet（Beta vulgaris L.）was used as the research material,the effects of salt stress on seedling growth and physiological characteristics under K⁺deficiency were analyzed.The gene structure,chromosome location,conserved motifs,cis-acting elements,phylogeny,and three-dimensional structure of BvHAK and BvHKT were systematically identified at the whole genome level.The expression patterns of BvHAKs and BvHKTs in different tissues of sugar beet under salt stress were analyzed by q RT-PCR.The objective of this study is to reveal mechanisms of these transporters in ion homeostasis and response to salt stress in sugar beet.（1）Adding 50 mmol·L^-1NaCl can significantly promote the growth of sugar beet seedlings,but the biomass and water content were decreased under high salt condition.Under K⁺deficiency,the dry weight,fresh weight,tissue water content,soluble sugar,sucrose,and glucose content of sugar beet seedlings were decreased,while the MDA content was increased,and the growth of sugar beet seedlings was inhibited.Under normal K⁺concentration,the dry weight,fresh weight,tissue water content,soluble sugar,sucrose,and glucose content of sugar beet seedlings under high salt stress were higher than those under K⁺deficiency,while MDA content was lower.The results showed that K⁺could effectively reduce the damage of sugar beet seedlings caused by salt stress.（2）A total of 10 BvHAKs were identified at the genome-wide level.BvHAK4,-5,-7 and-13 were located on the plasma membrane,other were located on the vacuole.Phylogenetic analysis showed that HAK could be divided into five subfamilies,cluster I（BvHAK5）,cluster III（BvHAK10）,cluster V（BvHAK9 and BvHAK12）,and cluster II was further divided into three subfamilies:IIA（BvHAK4,-7 and-13）,IIb and IIC（BvHAK2,-6 and-8）.In addition,the exon/intron number structure of BvHAK in each cluster is relatively conservative.Protein and protein interaction（PPI）prediction indicated that HAK could interact with K⁺channels TPK3 and AKT1,which suggested that the protein might be an important pivot in K⁺transport during the low potassium stress.（3）Three BvHKTs were identified at the genome-wide level and located on the plasma membrane.Phylogenetic analysis showed that HKT could be divided into two clusters.However,all BvHKTs belong to cluster I,and the exon/intron structure of the coding gene is relatively conservative.All members of BvHKT family contain the same PKD1 and PKD2 cation channel domains.It was predicted that the cis-acting elements of BvHKT could regulate various abiotic and biotic stresses in sugar beet.PPI analysis showed that all members of BvHKTs interacted with each other,and all members interacted with Na⁺/H⁺antiporters NHX1,NHX3,NHX4,NHX6 and NHX8,K⁺channel TPK3,and K⁺transporters KT1 and KT12.These results suggest that HKT may play an important role in regulating ion homeostasis under salt stress.（4）The expression pattern analysis showed that the members of BvHAKs family were up-regulated under salt stress,and the up regulation of BvHAK2,BvHAK5 and BvHAK7 were significant.In addition,under salt stress,the expression levels of BvHKT1;1,BvHKT1;2 and BvHKT1;3 in roots were significantly increased.Under high salt stress,HKT1 could unload Na⁺from xylem to roots,reduce the accumulation of Na⁺in shoot parts,and protect sugar beet leaves from salt toxicity.