Effect of mustard rhizobacteria on wheat growth promotion under cadmium stress: characterization of acdS gene coding ACC deaminase

Ten mustard rhizobacterial isolates that utilize 1-aminocyclopropane-1-carboxylate (ACC) as sole nitrogen source were screened for plant growth-promoting traits. These isolates enhanced root elongation significantly and minimized ethylene synthesis in wheat seedlings under induced cadmium stress condition. The presence of acdS gene coding for ACC deaminase was tested through gene-specific PCR amplification and further confirmed by nucleic acid hybridization. acdS gene from isolates Ps 2-3 and Ps 7-12 selected on the basis of wheat growth promotion was cloned and sequenced. Sequence analysis showed an open reading frame of 1017 bp encoding a complete polypeptide with an identity of 86.4 % between each other and sharing 84-95 % similarity with the earlier reported acdS genes. The deduced protein sequences were highly conserved and shared a 95.2 % homology at the amino acid level. Eight and thirteen new amino acid residues were found in the protein sequence of Ps 2-3 and Ps 7-12 with variation in numbers of different peptidase acting sites and protein motifs. Based on 16S rDNA sequencing, the isolates Ps 2-3 and Ps 7-12 were identified as Pseudomonas sp. and Pseudomonas fluorescens, respectively.