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.