CATALASE2 functions for seedling postgerminative growth by scavenging H2O2 and stimulating ACX2/3 activity in Arabidopsis

Increased fatty acid β‐oxidation is essential for early postgerminative growth in seedlings, but high levels of H2O2 produced by β‐oxidation can induce oxidative stress. Whether and how catalase (CAT) functions in fine‐tuning H2O2 homeostasis during seedling growth remain unclear. Here, we report that CAT2 functions in early seedling growth. Compared to the wild type, the cat2‐1 mutant, with elevated H2O2 levels, exhibited reduced root elongation on sucrose (Suc)‐free medium, mimicking soils without exogenous sugar supply. Treatment with the H2O2 scavenger potassium iodide rescued the mutant phenotype of cat2‐1. In contrast to the wild type, the cat2‐1 mutant was insensitive to the CAT inhibitor 3‐amino‐1,2,4‐triazole in terms of root elongation when grown on Suc‐free medium, suggesting that CAT2 modulates early seedling growth by altering H2O2 accumulation. Furthermore, like cat2‐1, the acyl‐CoA oxidase (ACX) double mutant acx2‐1 acx3‐6 showed repressed root elongation, suggesting that CAT2 functions in early seedling growth by regulating ACX activity, as this activity was inhibited in cat2‐1. Indeed, decreased ACX activity and short root of cat2‐1 seedlings grown on Suc‐free medium were rescued by overexpressing ACX3. Together, these findings suggest that CAT2 functions in early seedling growth by scavenging H2O2 and stimulating ACX2/3 activity. Fatty acid β‐oxidation is essential for early postgerminative growth in seedlings, but high levels of H2O2 produced by β‐oxidation can induce oxidative stress. Whether and how catalase (CAT) functions in fine‐tuning H2O2 homeostasis during seedling growth remain unclear. By using sucrose‐free 1/2 MS medium mimicking soils without exogenous sugars supply, our study showed that CAT2 plays an important role in early seedling growth by scavenging H2O2 and stimulating acyl‐CoA oxidase activity.