Ca ²⁺ Inhibits Stone Cell Formation in Pear by Suppressing PuMYB73 ‐ PuNAC21 ‐ PuLAC7 / PuPRX42 Module‐Mediated Lignin Deposition

Lignin deposition in stone cells is critical for pear fruit quality. However, calcium ions (Ca 2+ ) exert critical regulatory effects on fruit growth and development. Nevertheless, the molecular mechanisms underlying Ca 2+ ‐mediated stone cell formation in pear remain poorly characterized. Our study revealed that exogenous application of CaCl 2 decreased lignified stone cell formation in “Nanguoli” ( Pyrus ussuriensis ) fruits and significantly downregulated the expression of lignin biosynthesis‐related genes laccase7 ( PuLAC7 ) and peroxidase42 ( PuPRX42 ). Transcriptome sequencing (RNA‐seq) identified a transcription factor, PuMYB73, which was significantly inhibited by CaCl 2 in pear fruit stone cell formation and lignin accumulation. Yeast one‐hybrid (Y1H) and β‐glucuronidase (GUS) activity analysis revealed that PuMYB73 directly binds and activates lignin biosynthesis genes PuPRX42 and PuLAC7 promoters, thereby decreasing PuPRX42 and PuLAC7 expression after CaCl 2 treatment. Strikingly, PuMYB73 interacts with PuNAC21 to form a Ca 2+ ‐responsive module, lowering the transcription of PuPRX42 and PuLAC7 after Ca 2+ treatment, which contributed to decreasing pear stone cell production. Collectively, exogenous CaCl 2 treatment inhibits stone cell and lignin biosynthesis in pears mediated by the PuMYB73‐PuNAC21 regulatory module. Our results revealed that the Ca 2+ ‐PuMYB73‐PuNAC21‐PuLAC7/PuPRX42 regulatory module inhibits lignin biosynthesis, providing important insights into reducing stone cell content in pear via molecular breeding.