Comprehensive expression analysis of ERF transcription factors during chilling acclimation in Saintpaulia

Saintpaulia (Saintpaulia ionantha), a popular indoor ornamental potted plant, is native to the highlands of Kenya and Tanzania where temperatures rarely fall below 4 °C. Chilling injury during cultivation and transportation is a major commercial problem in Saintpaulia. In this study, we investigated chilling acclimation in Saintpaulia ‘Kilauea’. Plants grown at 20 °C (14 h light/10 h dark) displayed rapid and severe chilling injury after 24-h exposure to 4 °C. However, chilling injury at 4 °C could be dramatically reduced by pre-treating the plants at 10 °C but not at 6 °C. From whole genome analysis, 161 ethylene-responsive factors (ERFs) were identified and classified into 12 clades according to existing reports. Among these ERFs, 43, 8, and 4 ERFs were upregulated at 12, 24, and 48 h after 10 °C treatment, respectively. Most of these ERFs had GCC box and/or DRE/CRT core motifs-like sequences in their upstream regions. Finally, we compared the expression of ERFs between the treatments for 24 h at 10 °C, an effective temperature for chilling acclimation, and 6 °C, an ineffective temperature. The results showed that the expression of all six ERFs we investigated was increased by the 10 °C treatment, but not or only barely increased by the 6 °C treatment. This study suggests that Saintpaulia, a subtropical plant, can acclimate to low temperatures and that ERF upregulation is involved in chilling acclimation.