Fig. 7.

A proposed model depicting transgenerational thermomemory that is mediated by the H3K27me3 demethylation-HSFA2 regulatory loop in Arabidopsis. Long-term heat exposure activates plant heat sensor(s) that upregulates HSFA2, which targets and activates H3K27me3 demethylase REF6 and the chromatin remodeler BRM. REF6/BRM in turn triggers H3K27me3 demethylation to activate HSFA2. Thus, REF6 and HSFA2 form a heritable transcriptional feedback loop in heat responses and memory. This regulatory loop activates the E3 ligase, SGIP1, to trigger the transgenerational degradation of SGS3, leading to the suppression of tasiRNA biosynthesis. The REF6-HSFA2 loop and reduced tasiRNA levels converge to activate HTT5, which coordinates early flowering with decreased disease resistance in heat-stressed plants and progeny