Studies on expression of CBF1 and CBF2 genes and anti-oxidant enzyme activities in papaya genotypes exposed to low temperature stress

Abstract

Papaya, a crop of tropical and subtropical regions, is a herbaceous plant. Frost damage is a serious problem of papaya cultivation in sub-tropical areas. The C-repeat binding factor (CBF) genes are transcriptional activators that bind to the promoter regions of cold tolerance genes. The present experiment was conducted under completely controlled conditions of National Phytotron Facility, ICAR-IARI, New Delhi to understand the effect of temperature stress and its interaction in five papaya genotypes namely, Pusa Nanha, Red Lady, P-7-2, P-7-9, P-7-14 and one cold tolerant distant relative genus, i.e., Vasconcellea cundinamarcensis. RNA was isolated from all the above genotypes under control and low temperature stress conditions of 12° and 6 °C for 2 h and the expression analysis was done using quantitative Real-Time PCR (qRT-PCR). The expression of CBF2 was found to be the lowest in V. cundinamarcensis followed by P-7-9, while the highest in Red Lady. However the expression of CBF1 was observed to increase under the low temperature regimes and was maximum in V. cundinamarcensis and P-7-9, while minimum in Red Lady. This clearly explains the molecular basis of cold tolerance in V. cundinamarcensis and P-7-9 and cold susceptibility of Red Lady. The maximum activity of superoxide dismutase (SOD) was recorded in the V. cundinamarcensis (9.36 unit mg–1 TSP min–1), which was statistically different from all other genotypes. The highest mean activity of ascorbate peroxidase (APX) was observed in V. cundinamarcensis (5.79 unit mg–1 TSP) followed by P-7-9 (5.47 unit mg–1 TSP).