2.4 Heat priming and BRs promote the accumulation of dephosphorylated BES1 during memory phase
HS activates BES1 via dephosphorylation (Albertos et al., 2022), so we are curious about whether the state can be sustained in the memory phase. We executed a transient expression experiment on N. benthamiana leaves to explore the subcellular distribution of BES1 after heat priming. As shown in Fig. 3A, BES1 was diffused in the nucleus and cytoplasm prior priming, after exposure to 44℃ for 90 min, more BES1-GFP was shuttled to the nucleus, and the accumulation of BES1 in the nucleus could be maintained for another 2-3 d. BRs signal transduction activates BES1/BZR1 through releasing the inhibition of BIN2 thus promotes dephosphorylation of BES1, so we suppose BRs mediate thermomemory through promoting the accumulation of activated BES1 during the memory phase. We detected the abundance of de-phosphorylated BES1 in seedlings grown on solid plate medium with or without BL application during the memory phase. As shown in Fig. 3B, BL application strengthens the accumulation of dephosphorylated BES1, whereas BRZ (brassinazole, a specific inhibitor of BR synthesis) treatment impairs dephosphorylation. These results indicate that heat priming promotes the accumulation of dephosphorylated BES1 in the nucleus, BRs signal transduction further enhances this process.