Overexpression of a GmGBP1 ortholog of soybean enhances the responses to flowering, stem elongation and heat tolerance in transgenic tobaccos
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Soybean is a typical short-day crop, and its photoperiodic and gibberellin (GA) responses for the control of flowering are critical to seed yield. The GmGBP1 mRNA abundance in leaves was dramatically increased in short-days (SDs) compared to that in long-days in which it was consistently low at all time points from 0 to 6 days (days after transfer to SDs). GmGBP1 was highly expressed in leaves and exhibited a circadian rhythm in SDs. Ectopic overexpression of GmGBP1 in tobaccos caused photoperiod-insensitive early flowering by increasing NtCO mRNA levels. GmGBP1 mRNA abundance was also increased by GAs. Transgenic GmGBP1 overexpressing (-ox) tobacco plants exhibited increased GA signaling-related phenotypes including flowering and plant height promotion. Furthermore, the hypocotyl elongation, early-flowering and longer internode phenotypes were largely accelerated by GA3 application in the GmGBP1-ox tobacco seedlings. Being consistent, overexpression of GmGBP1 resulted in significantly enhanced GA signaling (evidenced suppressed expression of NtGA20ox) both with and without GA treatments. GmGBP1 was a positive regulator of both photoperiod and GA-mediated flowering responses. In addition, GmGBP1-ox tobaccos were hypersensitive to ABA, salt and osmotic stresses during seed germination. Heat-inducible GmGBP1 also enhanced thermotolerance in transgenic GmGBP1-ox tobaccos during seed germination and growth. GmGBP1 protein was localized in the nucleus. Analyses of a series of 5′-deletions of the GmGBP1 promoter suggested that several cis-acting elements, including P-BOX, TCA-motif and three HSE elements necessary to induce gene expression by GA, salicic acid and heat stress, were specifically localized in the GmGBP1 promoter region.
KeywordsGA signaling Photoperiod Soybean GmGBP1 gene Promoter Stem elongation Thermotolerance
This study was conducted in the Key Laboratory of Soybean Biology of Chinese Education Ministry, Soybean Research & Development Center, CARS and the key Laboratory of Northeastern Soybean Biology and Breeding/Genetics of Chinese Agriculture Ministry, financially supported by Chinese National Natural Science Foundation (31101169, 30671318,31271748), Chinese Key Projects of Soybean Transformation (2013ZX08004-005, 2013ZX08004-002), National 863 project (2013AA102602), Provincial/National Education Ministry for the team of soybean molecular design, Youth Backbone Research program of Provincial Education Department (1253G010), Northeast Agricultural University doctoral foundation. We thank Dr. Xuedong Wang for the help of scanning electron microscopy.
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