Physiological Mechanism of Callus Browning Resistance in Transformation of Indica Rice Yehong

Tissue culture and genetic transformation play important roles in functional genomics research and molecular breeding of rice. An efficient and versatile genetic transformation system has been developed for japonica rice but not for indica rice (Oryza sativa L.), which accounts for the majority of rice production. Callus browning is a key limiting factor in the transformation of indica rice. In our previous study, an indica line named Yehong (YH), which contains wild rice germplasm, was recognized for its large calli with compact cell arrangement, low browning rate, high regeneration capacity, and suitability for genome editing-based genetic transformation. Physiological and biochemical analyses of callus browning resistance revealed that YH exhibited lower H₂O₂ content, higher catalase (CAT) and glutathione reductase (GR) activities, reduced membrane lipid peroxidation, and lower ethylene accumulation than other cultivars. These results suggest that YH alleviates tissue browning likely by enhancing the scavenging of reactive oxygen species (ROS). RNA-seq analysis indicated that the browning resistance in YH may be associated with the regulation of plant hormones, oxidative stress response, and catalase activity. Furthermore, protein protein interaction (PPI) network analysis revealed six key genes potentially involved in callus browning and established a regulatory network centered on proteins related to oxidative phosphorylation, cytochrome C1, glutathione, and auxin. This study deepens our understanding of the physiological and molecular mechanisms underlying callus browning resistance in rice.