CsRBOH5.1 governs H3K4me3 and cold induced transcription during recovery after cold priming
Plants can maintain acquired cold tolerance after cold priming for a long period, even after resumption of warmer temperatures. However, the transcriptional mechanism during recovery after cold priming is rarely reported. Here, we found that in cucumber, cold priming altered the Histone H3 lysine 4 trimethylation (H3K4me3) signal of sustainably induced (memory) and non-sustainably induced (NSI) genes during recovery, and H3K4me3, on the upregulated memory gene, exhibited a specific epigenetic memory during recovery. However, the rank of the H3K4me3 signal on memory and NSI genes in the genome was independent of cold priming, which always contributed to and inhibited the formation of transcription patterns of memory and NIS genes, respectively. Further study revealed that short-lived increase of CsRBOH5.1 expression during recovery after cold priming was essential for cucumber maintaining a high-level of NADPH oxidase activity and apoplast H2O2 content, causing cucumber to acquire cold priming and enhancing the maintenance of acquired cold tolerance (MACT). Interestingly, the expression of some key H3K4me3 methyltransferase genes, and the accumulation of H3K4me3 on memory genes depended on CsRBOH5.1. Surprisingly, CsRBOH5.1 was essential for almost all genes to form the normal H3K4me3 signaling patterns during recovery, and the necessity was more obvious with the extension of recovery. Moreover, transcriptional-memory in Csrboh5.1 mutants was completely lost, and the transcriptional patterns of about 80% of NSI genes were disrupted. Generally, CsRBOH5.1 governed H3K4me3 and cold-induced transcription during recovery after cold priming, which affected the acquisition of cold priming and, in turn, affected the intension of MACT.