BcWRKY53 promotes chlorophyll biosynthesis and cold tolerance of non-heading Chinese cabbage under cold stress.

WRKY transcription factors are widely involved in plant responses to biotic and abiotic stresses, including cold stress. However, they have not been well studied in the regulation of chlorophyll synthesis and cold tolerance. So it is meaningful to analyze the mechanism under cold stress in non-heading Chinese cabbage. Here, BcWRKY53, a transcriptional activator WRKY-III gene, was identified by a screen upstream of the key chlorophyll synthesis genes BcCHLH and BcGUN4. BcWRKY53 was localized in the cell nucleus and induced to a significant extent by cold treatment. Ectopic expression of BcWRKY53 in Arabidopsis not only increased the chlorophyll content under cold stress, but also improved the cold tolerance. After silencing of BcWRKY53, there was a decrease in chlorophyll content and an increase in cold sensitivity. BcWRKY53 could inhibit self-expression by binding W-boxes in its own promoter. In addition, histone deacetylase 9 (BcHDA9) interacted with BcWRKY53 to inhibit BcWRKY53-mediated transcriptional activation. When ectopically overexpressed, BcHDA9 negatively regulates chlorophyll content and cold tolerance under cold treatment. Taken together, this study demonstrated that the cold-inducible transcription factor BcWRKY53 positively regulates BcCHLH and BcGUN4 under the regulation of self-regulation and BcHDA9 interactions. In this way, BcWRKY53 is actively involved in chlorophyll synthesis and the establishment of cold tolerance, which providing practical theoretical support in molecular characterization of cold tolerance and variety selection of non-heading Chinese cabbage.