Function Analysis Of Expansin Gene GmEXLB1 With High Phosphorus Efficient Utilization In Soybean

Soybean is an important food and oil crop in the world,while its growth and development was severely affected by the soil low phosphorus(P)stress.Plant roots are the major organ in response to low P signal,and the alteration of root architecture plays an important role in the resistance to the low P stress.Expansin is an important enzyme which involves in plant cell elongation,root architecture formation,and plays an important role in response to many abiotic stresses.In our previous study,some expansin genes from suppression subtractive hybridization(SSH)library of soybean variety under low phosphorus condition were obtained.Base on these,the objective of this study was to select and confirm the candidate expansin gene through the SSH and transcriptome data.Subsequently,the expansin gene was cloned,and identified with response to low P stress through the spatiotemporal expression and promoter analysis.And then,the transgenic Arabidopsis with GmEXLB1 overexpression was obtained,and the biological function of GmEXLB1 was analyzed.The results can provide functional gene for molecular breeding and mechanism analysis of plant high phosphorus efficiency.The main results are as follows:1.Expansin gene GmEXLB1 was obtained through the analysis of SSH library and transcriptome data of high phosphorus utilization soybean variety under low P condition.The expansin gene GmEXLB1 was highly expressed in soybean root at 28~70 days post low P stress(DPP)with the peak level at 49 DPP.Subsequently,the gene was cloned,and the results showed that GmEXLB1 contained four exons and three introns,with an open reading frame 744 bp that encoded 247 amino acids.Furthermore,the multiple alignment result showed that GmEXLB1 had the conserved domain of expansin protein and was highly homology with other plant expansins.2.Expansin gene GmEXLB1 was confirmed through spatiotemporal expression and promoter analysis.The results of real time quantitative PCR showed that GmEXLB1 was mainly expressed in soybean lateral roots,and was induced at 28~49 DPP,with the highest level at 42 DPP.Furthermore,the analysis of GmEXLB1 promoter showed that GUS histochemical staining was much stronger during the lateral root development under low P condition,compared with that under normal P condition.Meanwhile,the GUS histochemical staining was observed in the elongation zone of mature lateral root,which suggested that GmEXLB1 was mainly functioned in the elongation of plant cell in lateral root.3.The biological function of GmEXLB1 was revealed to play an important role in Pefficient utilization through the culture medium and pot experiments.The observation and measurement of Arabidopsis root morphology on culture medium showed that the transgenic plants displayed much longer length of primary root with 9.82%~13.14%,lateral roots with 38.06%~41.28%,and much numbers of lateral roots with 22.11%~31.73% than the wildtype under low P condition.Meanwhile,the results of micro-observation showed that the elongation region and cell length of lateral roots in transgenic lines increased by 21.71%~26.18%,14.18%~22.72% under low P condition.Furthermore,the analysis of phosphorus utilization efficiency in pot experiment showed that the shoot fresh weight,root fresh weight and phosphorus content in transgenic lines increased by 72.50%~168.33%,43.19%~106.57% and 152.00%~322.98%,respectively,compared with wild type under low P condition.All these results indicated that the expansin gene GmEXLB1 could improve phosphorus acquisition and utilization efficieny of transgenic plants under low P condition.Based on these results above,the conclusion was: Expansin gene GmEXLB1 was strongly induced by low phosphorus stress,especially in the elongation zone of lateral roots at 28 ~70 DPP.The open reading frame of GmEXLB1 is 744 bp,and the encoding protein has the conserved domain of plant expansins.Furthermore,the overexpression of GmEXLB1 can alter the root morphology and structure in transgenic Arabisopsis to improve Pacquisition and-utilization efficieny around the rhizosphere of transgenic plants under low phosphorus condition.