The glutathione S-transferase gene LaGSTU6 promotes somatic embryogenesis in a recalcitrant lily genotype by regulating scales redox homeostasis.

Abstract

Genotypic recalcitrance limits efficient somatic embryogenesis (SE). In this study, an SE induction system for the recalcitrant species Lilium amabile Palib. was established by modulating redox homeostasis. The first SE in this species was achieved by supplementing MS medium containing 1.0 mg·L^-1 picloram (PIC) with 150.0 mg·L^-1 glutathione (GSH), which increased SE induction rate from 0 to 33.3%. Physiological analysis revealed that GSH treatment upregulated endogenous GSH and key antioxidant enzymes, glutathione peroxidase (GPX) and glutathione S-transferase (GST). Specifically, their activities were elevated 1.9- and 9.8-fold higher, respectively, than those of control. This synergistic action scavenged hydrogen peroxide (H₂O₂), thereby alleviating oxidative stress. Furthermore, LaGSTU6 was identified as a core regulator of SE. In the SE-efficient lily Lilium martagon var. pilosiusculum Freyn, transient silencing of LaGSTU6 delayed embryogenesis initiation, caused severe browning, induced H₂O₂ accumulation, and reduced the antioxidant capacity, yielding a significant decrease in both the SE induction rate and efficiency. These findings preliminarily confirm that LaGSTU6 is a critical regulator of SE competence in lilies. Thus, we overcame genotypic recalcitrance and established the first SE induction system in Lilium amabile Palib. Our findings provide insights into the study of totipotency and inform strategies for regenerating recalcitrant germplasms.