Cloning and Characterization of a Maize cDNA Encoding Glutamate Decarboxylase

A putative glutamate decarboxylase (GAD) gene, designated ZmGAD1, was cloned from Zea mays with a combination of reverse-transcriptase polymerase chain reaction (RT-PCR) and bioinformatic approaches. The ZmGAD1 cDNA sequence contained a complete open reading frame encoding a putative protein of 496 amino acids, which contained a pyridoxal-5'-phosphate binding domain and a calmodulin (CaM)-binding domain found in nearly all GADs from plants. Sequence analysis showed that it had highest similarity with rice GAD1. Recombinant ZmGAD1 protein was expressed in Escherichia coli, purified and used to measure enzyme activity, which confirmed ZmGAD1 was really a glutamate decarboxylase gene. Southern blotting analysis suggested that ZmGAD1 was present as a single copy gene in the maize genome. RT-PCR analysis revealed that ZmGAD1 was expressed in all examined tissues including the roots, stems, leaves, ears, and tassels. The expression of the ZmGAD1 gene was upregulated and GAD activity was increased in the leaves and roots after treatment with ABA, MeJA, NaCl, PEG, or cold stress. Several stress-related cis-elements were present in the ZmGAD1 promoter cloned from maize genomic DNA. These results suggested that ZmGAD1 might play an important role in responses to abiotic factors and hormone treatments.