Evaluation Of Phosphorus Use Efficiency And Transcriptome Analysis In Barley Germplasm(Hordeum Vulgare L.)

Phosphorus dificiency is one of the major elements constraining plant growth and development.The area of phosphorus deficient soil is expanding,which severely affects agricultural production around the world.Generally,crop yield can be improved via application of fertilizer,which also triggers a series of problems such as environmental pollution.Phosphate rock,one of non-renewable resoueces,is the raw material of phosphate fertilizer and will be exhausted.Therefore,it is imperative to breed new varieties with high phosphorus efficiency.Barley,one of the earliest domesticated crops,is greatly accommodated and even known as ‘the last crop before the desert'.In the present study,two barley genotypes(GN121 and GN42)-with contrasting phosphorus efficiency-were selected from 150 barley accessions based on the results of phosphorus efficiency evaluation,and used to reveal comprehensive mechanisms in response to low phosphorus stress at the morphological,physiological,biochemical and molecular level.The main results are as follows:1.The pot experiment ? was conducted to evaluate the phosphorus use efficiency(PUE)among 150 barley genotypes based on their agronomic characters at mature stage under normal and low phosphorus conditions.The results indicated that all genotypes showed a significant difference in response to low phosphorus starvation,growth and yield of which were all suppressed and decreased.Compared with the control,the plant height,stemdiameter,spike length,grain number of the primary spike,total spike weight and thousand-grain weight of GN121 declined by 0.86,2.50,1.45,4.17,3.79 and 4.31%,respectively,and these measurements of GN42 fell sharply by 10.37,15.39,51.97,31.25,40.74 and 27.03%,respectively.Two candidate materials were identified,with variety GN121 achieving the highest tolerance,and GN42 being most sensitive.2.Two barley genotypes(GN121,low-P-tolerant,and GN42,low-P-sensitive)were applied to perform hydroponic experiment ? for analysis of their root morphological charaters.The results showed that the volume,surface area and total length of root reduced underphosphorus deficiency and varied between GN121 and GN42.These three indexes of GN121 decreased by 4.92,3.45 and 0.79% in comparison to control group,respectively,and which of GN42 declined sharply by 37.86,18.87 and 12.37%,respectively.Results indicated that GN42 showed more severe symptoms than GN121 did.Activity of protective enzymes and content of Chlorophyll,inorganic phosphorus and malondialdehyde(MDA)were measued in pot experiment ?,all of which were no remarkable differences in GN121 between normal and low phosphorus level,however,it is contrary to the results of GN42.MDA contents of GN121 increased less than that of GN42 under low phosphorus condition,and which of GN121 and GN42 increased most by 2.68% and 24.61% in comparison with the control,respectively.The expression pattern of Hv PT5 was investigated in the roots of GN121 and GN42 under different treatment conditions in hydroponic experiment ?.Following the extension of stress time,the relative expression level of Hv PT5 consistently increased in GN121 and decreased in GN42.3.Hydroponic experiment was conducted to analyse the characters of growth and physiology and biochemistry in GN121 and GN42 treated with normal and low(1/10 normal)phosphorus levels,which were calculated by the field fertilization of barley.The root growth of GN121 and GN42 at 19 d after phosphorus deficiency was significantly slower than that of the control groups,and a slight difference of shoot growth in GN42 occurred between normal and low phosphorus conditions.The growth of GN121 was remarkably less affected than that of GN42 by low phosphorus treatment for 90 days.Physiological and biochemical characters of GN121 and GN42 were analyzed at three time points(3rd,19 th day after phosphorus deficiency and 3rd day after phosphorus recovery).The results indicated that biomass,content of inorganic phosphorus and soluble sugar of GN121 and GN42 declined under phosphorus deficiency.Compared with the control,these three indicators of GN121 declined most by 7.69,26.18 and 16.33%,respectively,and which of GN42 fell sharply by 21.79,44.22 and 26.89%,respectively.However,the activity of acid phosphatase,relative conductivity and soluble protein content increased under phosphorus deficiency and varied between GN121 and GN42.These three indicators of GN121 increased most by 32.89,20.63 and 22.99% in comparison to control group,respectively,and which of GN42 elevated sharply by 26.04,45.46 and 64.80%,respectively.After 3 d of recovery,the changes of all parameters were opposite to that of low phosphorus stress except the continuous increase of the relativeconductivity.All indicators of GN121 are larger than that of GN42 except for relative conductivity under the same conditions.4.A multi-transcriptome database of barley in response to phosphorus starvation and recovery was firstly constructed by Illumina Hi Seq X ten and Pac Bio RS? SMRT platform.A total of 6,182 and 5,270 differentially expressed genes(DEGs)were identified in GN121 and GN42,respectively.The majority of these DEGs were involved in phosphorus metabolism such as phospholipid degradation,hydrolysis of phosphoric enzymes,sucrose synthesis,phosphorylation / dephosphorylation and post-transcriptional regulation,and expression level of these genes in GN121 was significantly higher than that in GN42.In addition,six and seven DEGs were annotated as phosphorus transporters in roots and leaves,respectively,and the expression patterns of which were quite different between GN121 and GN42.In the current research,the difference of phosphorus efficiency between GN121 and GN42 was studied from different aspects.In term of molecular level,genes related to phosphorus metabolism were identified,and the function and role of which still need to be further studied.