A PUB8-ZAT11/12-LAC1 module orchestrates ROS signaling-mediated stone cell differentiation

Stone cells are a specialized type of thick-walled plant cells that provide mechanical support and protect against pathogens and environmental stress. In pears, both the abundance and aggregation of stone cells significantly influence fruit quality. However, how ROS signals are transmitted to the terminal lignin polymerization machinery during stone cell formation remains unclear. Based on the spatial distribution patterns of stone cells, we investigated the relationships among stone cell content, reactive oxygen species (ROS) levels, and programmed cell death (PCD) events in young fruits. Gene co-expression network analysis identified two ZAT family members, PbZAT11 and PbZAT12. Biochemical analyses revealed that ROS enhance the expression of PbZAT11 and PbZAT12. PbZAT11 and PbZAT12 directly activate PbLAC1 expression and promote lignin polymerization. In contrast, PbPUB8 negatively regulates stone cell formation in pear fruits by mediating the ubiquitination and degradation of PbZAT11 and PbZAT12. Our findings identify a ROS-responsive regulatory module in which PbZAT11 and PbZAT12 directly activate PbLAC1 to promote lignin biosynthesis, while PbPUB8 negatively regulates this process by targeting PbZAT11/12 for ubiquitination and degradation. This coordinated activation-degradation mechanism provides new insights into the regulation of stone cell formation in pear fruit.