Upregulation of PpHsfB2b at high temperature represses light-induced anthocyanin biosynthesis in pear

In recent years, escalating global temperatures have adversely affected the yield and quality of horticultural crops. Red pears (Pyrus spp.), prized for their vibrant pigmentation, derive their characteristic coloration primarily from anthocyanin accumulation. Light and temperature are important environmental factors regulating anthocyanin biosynthesis. Light induces the accumulation of anthocyanins in red pear; however, the specific molecular mechanism by which elevated temperatures inhibit anthocyanin biosynthesis in red pear remains unclear. The integration nodes of the light and temperature signals also remain to be discovered. In this study, we identified a high-temperature-responsive repressor, pear HEAT SHOCK FACTOR B2b (PpHsfB2b), which exhibits rapid upregulation under high-temperature treatment. A stable transformation system using pear calli demonstrated that PpHsfB2b functions as a repressor of anthocyanin biosynthesis. PpHsfB2b directly bound to the promoters of anthocyanin biosynthesis-promoting factors MYB transcription factor 10 (PpMYB10) and ELONGATED HYPOCOTYL 5-LIKE (PpHY5L), inhibiting their expression. Additionally, we identified a key light-temperature signaling node gene, B-box transcription factor 16 (PpBBX16), through which PpHsfB2b exerts a dual inhibitory effect on anthocyanin biosynthesis. PpHsfB2b not only interacted with PpBBX16 to attenuate transcriptional activation of downstream genes PpMYB10 and UDP-glucose: flavonoid 3-O-glucosyltransferase (PpUFGT), but also suppressed anthocyanin accumulation by competitively weakening the PpHY5L-PpBBX16 interaction. These insights deepen our understanding of high-temperature-regulated fruit pigmentation and identify PpBBX16, a critical light-temperature signaling node, providing a molecular framework for the color change of pear fruits under increasing temperatures.