2.2 BES1 is specifically required for thermomemory
Given that BRs act positively in thermomemory, we then investigated whether the defect in BRs synthesis weakened memory response. Previous studies reported that BR-deficient and -overproduction seedlings represented similar thermal tolerance (Albertos et al., 2022; Mazorra et al., 2011), to further investigate whether endogenous BRs levels affect thermomemory, we subject 5-day-old det2 and DET2-OXseedlings to our priming and triggering stimulus protocol. Surprisingly, both det2 and DET2-OX represented enhanced thermal tolerance (Supplementary Fig. 1), indicating that thermomemory is also independent of BR homeostasis, this promotes us to explore downstream of BRs signaling. We next access the role BES1 acts in thermomemery since the effect of BRs is largely mediated by the BES1/BZR1 subfamily transcription factors. Considering the functional redundancy between BES1 and BZR1, we chose BES1-RNAi (a mutant BES1/BZR1 mRNA almost undetectable caused by RNA interference) to carry out thermomemory assay (Yin et al., 2005). As shown in Fig. 1, BES1 deficiency caused seedlings hypersensitive to heat, as comparably declined survival rate and increased electrolyte leakage was detected in BES1-RNAi . In contrast to the elevated thermotolerance by priming stimulation in Col-0, primed BES1-RNAi seedlings represent similar thermotolerance to the unprimed, indicating that BES1/BZR1 is required for thermomemory. Application of 10 nM BL increased the survival rate of Col-0 seedlings, however, it had no obvious effect on BES1-RNAiunder both primed and unprimed conditions. These results suggest that BES1 is indispensable for BRs-enhanced thermomemory.