Lateral Root Response To Phosphorus Deficiency Of Maize And Its Physiological And Biochemical Mechanism

As an essential element in plants,phosphorus easily chelate with other elements in soil,forming sparingly soluble phosphorus which leads to the low phosphorus availability.Large amounts of phosphorus in soil cannot be used efficiently by crops and that seriously constrains the food production in the farmland in China.Root system is a vital organ for the water and nutrient uptake of crops.It is very important to improve the uptake and utilization of phosphorus by improving the root exploration of phosphorus in topsoil and the mobilization of sparingly soluble phosphorus.Root system of maize belongs to fibrous root system,in which the lateral root plays an important role for the absorption of water and nutrients.We studied the response of maize lateral root to phosphorus deficiency and its physiological and biochemical mechanism,which was beneficial to explore the potential of maize root system to improve phosphorus uptake and grain yield of maize.This study was conducted from 2016 to 2019 in Experimental Farm of Shandong Agricultural University,the Larson Agricultural Research Center of the Pennsylvania State University and State Key Laboratory of Crop Biology.We selected the maize inbred line of B73 and Mo17 and its recombinant inbred lines(many short lateral roots,MS;few long lateral roots,FL)as the material.Two phosphorus level of high phosphorus(HP)and low phosphorus(LP)was designed for the hydroponics,greenhouse and field.All the experiment was randomized complete block design.Our study employed the method of the plant physiology,biochemistry and molecular biology,analyzing the root architecture,root anatomy,root respiration,root H⁺-flux,plant nutrient content,root transcriptome,root metabolome of diffenent maize inbred lines under low phosphorus conditions.The results as followed:1.Root system response to phosphorus deficiencyPhosphorus deficiency decreased the lateral root branching density and total lateral root length of maize.MS lines obtained significantly higher lateral root branching density of crown root than FL lines,6.9 vs 5.9 branches cm^-1 respectively.MS lines had significant total lateral root length and root length densith in topsoil than FL lines,incerasing by 42.2%and 138.6%respectively.MS lines decreased the root depth and formed a shallow root system,improving the topsoil exploration of root.Phosphorus deficiency significantly increased the root cortical aerenchyma percentage and root respiration.Under low phosphorus conditions,MS lines had significant higher the root cortical aerenchyma percentage than FL lines,increasing by 86.3%;MS lines had significant lower root respiration than FL lines,decreasing by 41.0%.Under low phosphorus conditions,MS lines increased the phosphorus uptake,leaf chlorophyll content and photosynthetic rate,and thus increased the shoot biomass and grain yield.Under low phosphorus conditions,Mo17 significantly increased the lateral root length and lateral root surface area of 0.5-0.75 mm root diameter,increasing by 139.8%and 145.7%than B73;Mo17 had higher total lateral root length and lateral root surface area than B73,increasing by 8.1%and 33.0%.Thus,Mo17 located more carbon to the lateral roots under phosphorus conditions.In the meanwhile,under low phosphorus conditions,Mo17 formed more root aerenchyma of axial root,decreasing root respiration;Mo17 increased the H⁺efflux rate.Under low phosphorus conditions,Mo17 increased the phosphorus and nitrogen uptake.2.The molecular mechanism of maize root response to phosphorus deficiencyWe studied the transcriptome after low phosphorus treatment of 2 h,1 d and 5 d.After low phosphorus treatment of 2 h,B73 and Mo17 identified the most differentially expressed genes(DEGs),1758 and 3513.Gene ontology(GO)and KEGG enrichment was analyzed.After low phosphorus treatment of 2 h,1 d and 5 d,Mo17 was significantly enriched to 47,34 and 20entries,respectively;the significant enrichment of GO item included the oxidoreductase activity,DNA binding,response to gibberellin,carbohydrate transport,cellular response to phosphate starvation and acid phosphatase activity;B73 was significantly enriched to 45,25and 17 entries,respectively;the significant enrichment of GO item included response to oxidative stress,the oxidoreductase activity,cytokinin metabolic process,carbohydrate transport,cellular response to phosphate starvation.After low phosphorus treatment of 2 h,1 d and 5 d,Mo17 was significantly enriched to 20,21 and 10 KEGG pathway,respectively;the significant enrichment of KEGG pathway included biosynthesis of secondary metabolites,plant hormone signal transduction,phenylpropanoid biosynthesis,starch and sucrose metabolism,flavonoid biosynthesis,cysteine and methionine metabolism,Starch and sucrose metabolism,glutathione metabolism,nitrogen metabolism.Mo17 was significantly enriched to 14,9 and 16KEGG pathway,respectively;the significant enrichment of KEGG pathway included biosynthesis of secondary metabolites biosynthesis of secondary metabolites,phenylpropanoid biosynthesis,cysteine and methionine metabolism,flavonoid biosynthesis,carbon metabolism,plant hormone signal transduction,nitrogen metabolism.Under phosphorus deficiency,Mo17could induce the differentially expressed transcription factors(TF)of NAC,SPX,SAUR,TIFY,b HLH,MYB,WRKY and LPR,regulate the hormonal signal pathways related to auxin,abscisic acid and jasmonic acid,and thus regulate the root growth.After low phosphrus treatment of 5 d,Mo17 upregulated MHA5;after low phosphorus treatment of 2 h and 1 d,Mo17 upregulated the Zm PHT1;13 and purple acid phosphatase,while B73 downregulated the Zm PHT1;13 after low phosphorus treatment of 2 h.Thus Mo17 improved the phosphorus mobilization and uptake of root.Under phosphorus deficiency,Mo17 and B73 had 159 and 149 different metabolite,respectively,in which Mo17 and B73 had 72 common different metabolite.Under low phosphorus conditions,Mo17 and B73 downregulated the glucose-1-phosphate,trehalose 6-phosphate and D-glucose-6-phosphate,indicating root recovered phosphorus from small molecular weight phosphorylated metabolites to maintain important cellular functions.Under low phosphorus conditions,Mo17 decreased the level of D-glucose,and Mo17 located more carbohydrates to root for growth.Mo17 significantly enriched the metabolic pathway of flavone and flavonol biosynthesis,starch and sucrose metabolism,pentose and glucuronate interconversions,amino sugar and nucleotide sugar metabolism.B73 significantly enriched the metabolic pathway of anthocyanin biosynthesis,starch and sucrose metabolism.