Hydrogen peroxide homeostasis provides beneficial micro-environment for SHR-mediated periclinal division in Arabidopsis root

The precise regulation of asymmetric cell division (ACD) is essential for plant organogenesis. In Arabidopsis roots, SHORT-ROOT (SHR) functions to promote periclinal division in cortex/endodermis initials, which generate the ground tissue patterning. Although multiple downstream transcription factors and interplaying hormone pathways have been reported, the cellular mechanism that affects SHR-mediated periclinal division remains largely unclear. Here, we found that SHR can substantially elevate reactive oxygen species (ROS) levels in Arabidopsis roots by activating respiratory burst oxidase homologs (RBOHs). Among the ROS products, hydrogen peroxide (H₂ O₂ ) rather than superoxide (O₂^- ) was shown to play a critical role in SHR-mediated periclinal division. Scavenging H₂ O₂ could markedly impair the ability of SHR to induce periclinal division. We also show that salicylic acid (SA) can promote H₂ O₂ production by repressing CAT expression, which greatly increased periclinal division in root endodermis. As a result, middle cortex was more frequently formed in the endodermis of snc1, a mutant with accumulated endogenous SA and H₂ O₂ . In addition to RBOHs, SHR also activated the SA pathway, which might contribute to the elevated H₂ O₂ level induced by SHR. Thus, our data suggest a mechanism by which SHR creates the optimal micro-environment for periclinal division by maintaining ROS homeostasis in Arabidopsis roots.