PbrMYB4, a R2R3-MYB protein, regulates pear stone cell lignification through activation of lignin biosynthesis genes

• Published in: Horticultural Plant Journal
• Main Authors: Dongliang Liu, Yongsong Xue, Runze Wang, Bobo Song, Cheng Xue, Yanfei Shan, Zhaolong Xue, Jun Wu
• Format: Article
• Language: English
• Published: KeAi Communications Co., Ltd. 2025-01-01
• Subjects: Pear; Stone cell; R2R3-MYBs; Lignin
• Online Access: http://www.sciencedirect.com/science/article/pii/S2468014124000049

Pear (Pyrus bretschneideri) fruit stone cells are primarily composed of lignin and have strongly lignified cell walls. The presence of stone cells has a negative influence on fruit texture and taste, and thus the reduction of stone cell content in pear fruit is a key goal of breeding efforts. However, research into the key transcription factors and regulatory networks associated with pear fruit stone cell formation have been limited. We here used a combination of co-expression network and expression quantitative trait locus (eQTL) analyses in 206 pear cultivars with different stone cell contents to identify relevant genes; these analyses uncovered the gene PbrMYB4, a R2R3 MYB transcription factor gene. There was a strong positive correlation between relative PbrMYB4 expression levels in the fruit flesh and stone cell/lignin contents. Overexpression of PbrMYB4 significantly increased the lignin contents, whereas silencing of PbrMYB4 had the opposite effect, decreasing the contents of lignin. PbrMYB4 overexpression in pear calli significantly promoted lignin biosynthesis. In Arabidopsis thaliana, PbrMYB4 overexpression resulted in increasing lignin deposition, cell wall thickness of vessels and xylary fiber, and accelerating expression level of lignin biosynthetic genes. PbrMYB4 was found to activate 4-Coumarate:Coenzyme A Ligase (Pbr4CL1) by binding to AC-I elements in the promoter regions, as demonstrated with dual-luciferase reporter assays and a yeast one-hybrid assay. These results demonstrated that PbrMYB4 positively regulated lignin biosynthesis in pear fruit stone cells by activating lignin biosynthesis genes. This study improves our understanding of the gene regulatory networks associated with stone cell formation in pear fruit, providing guidance for molecular breeding of pear varieties with low stone cell content.