Fig. 10

A model for the primed transcriptional responses from specific dehydration stress response genes. JA-primed dehydration stress response genes are not transcribed under watered conditions (W). The ABFs and MYC2 transcription factors are inactive. Treatment with JA activates MYC2 enabling it to bind the MED25 subunit of the complex and to recruit it to the specific promoters (W + JA). MEDIATOR stimulates the assembly of PIC and the installment of activated (Ser5-P) Pol II at the TSS marked with arrow [+1]. Ser5-P Pol II recruits histone K4 methyltransferases (KTM) establishing the H3K4me3 marks at 5′-end nucleosomes. Pol II remains in activated (paused, or stalled) state unable to initiate transcription before a dehydration stress; H3K4me3-modified nucleosomes and Pol II remain at the 5′-gene’s after removal of JA (RJ1) and in the absence of transcription. TBP, MEDIATOR, and MYC2 do not fully dissociate from the promoter in RJ1. Upon dehydration stress (S1J1), the levels of endogenous ABA increase activating the ABFs. The levels MEDIATOR and MYC2 also increase, but the nature of their interactions with the ABFs is unclear at present (shown with dashed arrows). H3K4me3 and Ser5P Pol II also increase and transcription is induced. The possibility that ABFs recruit key elongation factors to release stalled Pol II into active transcription is indicated by a dashed line