PbMADS49 Regulates Lignification During Stone Cell Development in 'Dangshansuli' (Pyrus bretschneideri) Fruit

Lignified stone cell content is one of the critical factors affecting 'Dangshansuli' fruit quality. The function of MADS-box transcription factors in regulating lignin biosynthesis in pear fruit is still less. In this study, PbMADS49 gene silencing inhibited the lignin biosynthesis and stone cell secondary wall development of pear fruit mainly through reducing the expression levels of lignin monomer polymerisation key enzymes (PbPRX33 and PbPRX45). PbMADS49 was a transcriptional repressor inhibiting its transcription by binding to the CArG element in the target gene promoter. Combined with the co-expression network and promoter cis-acting element analysis, we hypothesised that PbMADS49 positively regulates the transcription of PbPRX33 through PbWRKY63. The gene silencing effect of homologous genes PbPRX33-1 and PbPRX33-2 was consistent with PbMADS49, and PbPRX33-2 was more significant than PbPRX33-1. This study shows that PbMADS49 is a positive regulator of stone cell lignification, providing new insights into the development mechanism of pear stone cells.