MYB14– PAL1 Modulates the Role of Jasmonic Acid in the Biosynthesis of Lignin in Apple Fruit Russeting Induced by Mechanical Damage

Jasmonic acid (JA) signaling induced by mechanical damage to plants leads to lignin deposition. Mechanical damage is a critical contributing factor to fruit russeting, but the underlying molecular mechanism remains unclear. Here, we found that the lignin content increased significantly during apple fruit russeting with mechanical damage. The expression of structural genes in lignin biosynthetic pathways in russeted fruits increased, especially MdPAL1. The transcription factor MdMYB14 was induced by JA and bound to the P1 site of the AC element in MdPAL1 promoter to activate its expression. The content of various jasmonates increased in russeted fruits, and the lignin content of apple increased after JA treatment. MdMYB14 positively regulated lignin biosynthesis, which partially depended on MdPAL1. These findings reveal the molecular mechanism that MYB14–PAL1 mediates the role of JA in mechanical damage-induced lignin biosynthesis in apple fruit russeting and will aid the development of strategies to control russeting.