Abstract：Pectin methylesterase (PME) is a cell wall-localized protein associated with aluminum tolerance of plant. Tamba Black soybean (Glycine max cv. Tamba) belongs to leguminous plants and has great potential for aluminum tolerance. To study the function of GmPME2 (GenBank No. MN867684) in Tamba Black soybean under aluminum stress, this research cloned one of Tamba Black soybean's gene of GmPME2 by using reverse transcription PCR (RT-PCR). The coding regions of GmPME2 was 900 bp in length and encoded a protein of 299 amino acids with the isoelectric point of 8.85. GmPME2 was a stable protein with instability coefficient of 30.11<40. The expression analyses of GmPME2 in Tamba Black soybean challenged by Al3+ (pH4.5, 0.5 mmol/L CaCl2, 50 μmol/L AlCl3) showed an upregulation of GmPME2 within 12 h and downregulation from 12~24 h with the highest spot on the 12 h. Expression of GmPME2 in roots was significantly higher than that in stems or leaves (P<0.05), especially in root tips. Transient expression of tobacco (Nicotiana benthamiana) revealed that GmPME2 protein was located in cell wall. The expression vector, pBI121-GmPME2-eGFP, was constructed and transformed into tobacco by Agrobacterium mediated transformation and subsequently obtained transgenic tobaccos. Three transgenic tobaccos (GmPME2-1, GmPME2-3 and GmPME2-4) were selected to investigate the aluminum tolerance, The results showed that the relative expression of GmPME2 increased significantly (P<0.05), GmPME2 activity and malondialdehyde (MDA) content in root tips had remarkable decrease in root relative elongation compared to wild type (WT). Hematoxylin and Evans blue staining revealed a deeper stain in transgenic tobacco than that in WT. Compared with WT, the secretion of citrate in transgenic tobacco root tips significantly increased due to more aluminum absorption (P<0.05). This research indicated that plant could enhance its aluminum tolerance by decreasing aluminum absorption in root tips via regulating the expression of PME2 gene which provides the genetic resources for researches in aluminum toxicity.
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