Overexpression of tobacco osmotin (Tbosm) in soybean conferred resistance to salinity stress and fungal infections

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Abstract
Salinity and fungal diseases are the two significant constraints limiting soybean productivity. In order to address these problems, we have transformed soybean cv. Pusa 16 via somatic embryogenesis with salinity induced and apoplastically secreted pathogenesis-related tobacco osmotin (Tbosm) gene using Agrobacterium-mediated genetic transformation. Integration of Tbosm in randomly selected five GUS assay-positive independently transformed soybean plants was confirmed by polymerase chain reaction (PCR) and Southern hybridization. Reverse transcriptase-PCR (RT-PCR) and Western blotting confirmed that the Tbosm was expressed in three of the five transformed soybean plants. Further the Western blotting revealed that the truncated osmotin protein accumulated more in apoplastic fluid. The transformed (T1) soybean plants survived up to 200 mM NaCl, whereas non-transformed (NT) plants could withstand till 100 mM and perished at 150 mM NaCl. The biochemical analysis revealed the T1 soybean plants accumulated higher amount of proline, chlorophyll, APX, CAT, SOD, DHAR, MDHAR, and RWC than NT plants. Leaf gas exchange measurements revealed that T1 soybean plants maintained higher net photosynthetic rate, CO2 assimilation, and stomatal conductance than NT plants. The three T1 soybean plants expressing the osmotin gene also showed resistance against three important fungal pathogens of soybean—Microsphaera diffusa, Septoria glycines and Phakopsora pachyrhizi. The T1 soybean plants produced 32–35 soybean pods/plant containing 10.3–12.0 g of seeds at 200 mM NaCl, whereas NT plant produced 28.6 soybean pods containing 9.6 g of seeds at 100 mM NaCl. The present investigation clearly shows that expression of Tbosm enhances salinity tolerance and fungal disease resistance in transformed soybean plants.

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