Expression of bacterial L-aspartate-α-decarboxylase in tobacco increases β-alanine and pantothenate levels and improves thermotolerance

L-Aspartate-alpha-decarboxylase catalyzes the decarboxylation of L-aspartate to generate beta-alanine and carbon dioxide. This is an unusual pyruvoyl-dependent enzyme unique to prokaryotes that undergoes limited self-processing. The Escherichia coli panD gene encoding L-aspartate-alpha-decarboxylase was expressed under a constitutive promoter in transgenic tobacco. Transgene expression was verified by assays based on RNA blots, immunoblots and enzyme activity in vitro. The panD lines had increased levels of leaf beta-alanine (1.2- to 4-fold), pantothenate (3.2- to 4.1-fold) and total free amino acids (up to 3.7-fold) compared to wild-type and vector controls. Growth of homozygous lines expressing E. coli L-aspartate-alpha-decarboxylase was less affected than that of the control lines when the plants were stressed for 1 week at 35 degrees C. When transferred from 35 to 30 degrees C for 3 weeks, the PanD transgenic lines recovered significantly (P <= 0.001) better than the controls: PanD lines had on an average 54% and 84% greater fresh and dry weights respectively, compared to the controls. Homozygous lines expressing E. coli L-aspartate-alpha-decarboxylase had significantly greater thermotolerance (P <= 0.05) during germination. At 42 degrees C, 95% of two T3 PanD transgenic line seeds germinated after 12 days compared to 73% for the wild-type seeds. Our results indicated that E. coli L-aspartate-alpha-decarboxylase was correctly processed and active in the transgenic eukaryotic host and its expression resulted in increased thermotolerance in tobacco.