Exogenous expression of ACC deaminase gene in psychrotolerant bacteria alleviates chilling stress and promotes plant growth in millets under chilling conditions

Abstract

Endogeneous ethylene evolved during cold stress is a major limiting factor for plant growth which can be controlled by bacterial enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCD), by breaking down ACC, the precursor of ethylene. In the present study, we introduced ACCD expressing plasmid in ACCD negative psychrotolerant bacteria to study its effect on growth of finger and foxtail millet seedlings. ACCD negative <i>Sphingomonas </i> faeni ISO were selected and transformed with plasmid pRKACC containing the <i>acdS </i> gene. Inoculation of the millet seeds and studying physiological parameters when a cold stress of 4 and 10ºC was imposed showed that inoculation with ACCD expressing strains improved root and shoot length, biomass content of foxtail and finger millets seeds. Further, we also observed increased antioxidant activity in the plants by high levels of SOD, CAT, GPX, POD, APX and GR enzyme activity, and decreased proline content on inoculation with ACCD positive mutants. The enzyme ACC deaminase is thus be proved to be a potential strategy to alleviate cold stress in foxtail and finger millet by regulating endogenous ethylene evolved during stress conditions.