Reduced proteasome degradation of HsfB2a at higher temperatures is responsible for the inhibition of anthocyanin synthesis in pear

Global climate change has led to unpredictable and frequent high temperatures in summer and autumn, which correlates with an undesired reduction in anthocyanin accumulation in fruit crops. The regulatory mechanisms for high-temperature-repressed anthocyanin synthesis in pear (Pyrus spp.) remain largely unidentified. We found that high-temperature signaling inhibits anthocyanin biosynthesis in pear at the transcriptional and posttranslational levels. We discovered that pear HEAT SHOCK FACTOR B2A (PpHsfB2a) inhibits transcription of ELONGATED HYPOCOTYL 5-LIKE (PpHY5L), a major activator of light-regulated anthocyanin biosynthesis, by binding to a heat shock element in its promoter, ultimately inhibiting anthocyanin accumulation. At high temperatures, PpHsfB2a protein abundance rises significantly due to reduced degradation via the 26S proteasome pathway, likely mediated by the RING-type E3 ubiquitin ligase PpATL52, a homolog TOXICOS EN LEVADURA 52 from Arabidopsis thaliana. High temperatures inhibited PpATL52 expression and protein levels, causing PpHsfB2a accumulation and reduced anthocyanin production. In summary, we discovered a PpATL52-PpHsfB2a-PpHY5L module that responds to high temperatures and inhibits anthocyanin biosynthesis, which may be causal for climate change-related changes in fruit quality in pear.