ERF109 of trifoliate orange (Poncirus trifoliata (L.) Raf.) contributes to cold tolerance by directly regulating expression of Prx1 involved in antioxidative process

Summary Ethylene‐responsive factors ( ERF s) have been revealed to play essential roles in a variety of physiological and biological processes in higher plants. However, functions and regulatory pathways of most ERF s in cold stress remain largely unclear. Here, we identified Ptr ERF 109 of trifoliate orange ( Poncirus trifoliata (L.) Raf.) and deciphered its role in cold tolerance. Ptr ERF 109 was drastically up‐regulated by cold, ethylene and dehydration, but repressed by salt. Ptr ERF 109 was localized in the nucleus and displayed transcriptional activity, and the C terminus is required for the activation. Overexpression of Ptr ERF 109 conferred enhanced cold tolerance in transgenic tobacco and lemon plants, whereas VIGS (virus‐induced gene silencing)‐mediated suppression of Ptr ERF 109 in trifoliate orange led to increased cold susceptibility. Ptr ERF 109 overexpression caused extensive transcriptional reprogramming of several suites of stress‐responsive genes. Prx1 encoding class III peroxidase ( POD ) was one of the antioxidant genes exhibiting the greatest induction. Ptr ERF 109 was shown to directly bind to the promoter of PtrPrx1 (trifoliate orange Prx1 homologue) and positively activated its expression. In addition, the Ptr ERF 109 ‐overexpressing plants exhibited significantly higher POD activity and accumulated dramatically less H 2 O 2 and were more tolerant to oxidative stress, whereas the VIGS plants exhibited opposite trends, in comparison with wild type. Taken together, these results indicate that Ptr ERF 109 as a positive regulator contributes to imparting cold tolerance by, at least partly, directly regulating the POD ‐encoding gene to maintain a robust antioxidant capacity for effectively scavenging the reactive oxygen species. Our findings gain insight into better understanding of transcriptional regulation of antioxidant genes in response to cold stress.