CaCRF6, A Cytokinin Response Factor, Confers Cold Tolerance in Capsicum

Cytokinin response factors (CRFs), a subfamily attached to the transcription factor AP2/ERF family, are extensively involved in the responses to abiotic stresses in plants. However, the role of CRFs in cold tolerance remains poorly characterized in Capsicum. In this study, the cold tolerance of 14 accessions was screened in Capsicum, and it was found that accession C3 displayed strong cold tolerance, while accession C88 exhibited opposite characteristics. Transcriptome profiling revealed that 2223 genes, including 897 up-regulated and 1326 down-regulated genes, were commonly differentially expressed (DEGs) in response to cold treatment in both C3 and C88. It was interesting that the plant-pathogen interaction was among the most significant pathways. Notably, the expression of CaCRF6 was obviously up-regulated in C3 (92.80-fold) than that in C88 (4.04-fold) at cold treatment, which suggested that CaCRF6 was closely related to cold tolerance in Capsicum. Subsequently, CaCRF6 was silenced by Virus-induced gene silencing to study its function at cold stress, and the results showed that silencing CaCRF6 reduced cold tolerance of C3, accompanied by the increases in content of malondialdehyde, electrolyte leakage, and reactive oxygen species, as well as a decrease in the maximal photochemical efficiency of PSII. These results indicate that CaCRF6 plays a critical role in coping with cold stress in Capsicum, which provides new insights into understanding cold tolerance in Capsicum.