GSX1 and hyperinsulinemic hypoglycemia, familial, 4: However, the upregulated FRO2 expression under S deficiency disappeared in the sir1-1, cad2-1, and s1c2, suggesting that the expression of FRO2 may be directly or indirectly dependent on GSH1 and/or SIR. Moreover, given the fact that the sir1-1, cad2-1, and s1c2 seedlings are already suffering from S deficiency even under normal growth conditions (Speiser et al., 2018), the reduced expression of FRO2 in the sir1-1, cad2-1, and s1c2 seedlings compared to Col-0 suggest that under severe/prolonged S starvation, the expression of FRO2 is downregulated as a consequence of secondary adaptations.